Materials and devices for energy and environment applicationsK
Photonic materials and techniques for SERS and solar cell light trapping
Introduction and scope:
Both photovoltaics and SERS share many materials and technologies for light management, of which both communities can profit from a shared knowledge. This symposium will provide a platform for discussion on the wide range of materials, techniques and application possibilities for light trapping and scattering structures.
This symposium is focused in materials and methods for the fabrication of Photonic surfaces for Solar Cells and for Surface Enhanced Raman Spectroscopy (SERS).
Light management is regarded as the most promising route to decrease the cost of photovoltaics (PV) and foster its market implementation. Optimized light trapping strategies have the potential to strongly boost the optical absorption in the thin solar cell material, thereby enhancing the efficiency and allowing the thickness reduction. Fabrication methods (such as surface texturing, diffraction gratings, dielectric wavelength-sized particles and nano-dome arrays, photonic crystals or plasmonic structures) are nowadays regarded as promising strategies to achieve light path length enhancement, anti-reflection, light focusing, etc. Some light scatterers work best in the rear of the cells, while others are preferable for the front. These issues should be addressed. Surface Enhanced Raman Spectroscopy is a widely spread technique that takes profit of plasmonic materials to observe of a low number of molecules down to the individual molecule. One of the most developed applications is the use of SERS substrate in plasmonic nanosensors since they can provide high sensitivity, allowing the detection of biological or chemical species at low concentration. However, in order to be able to have reproducible and low cost SERS substrate, it is necessary to propose some new methods and materials that allows the production of plasmonic nanostructures on large surfaces with high SERS enhancement capability and with high throughput. Patterning and fabrication techniques such as nano-imprint, self-assembly, etc that can allow the production of reproducible cost-efficient SERS substrates are envisaged. Synthesis of metal nanoparticles and cleaning procedures to remove capping agents from the nanoparticles are targeted. Removal of these species is particularly important for their use as SERS platforms, since these may not only give an interfering signal, but also they may prevent close contact between the surface and the analyte, and thus an optimal signal-enhancement.
Symposium presenters are invited to submit Feature Article or Original Paper manuscripts for publication. These will be considered as regular submissions to a topical section in pss (a) – applications and materials science (http://www.pss-a.com).
Hot topics to be covered by the symposium:
- Substrates for SERS - Surface Enhanced Raman Spectroscopy
- Light trapping strategies for solar cells
- Nanoimprint lithography
- Dielectric photonic structures
- Plasmonic solar cells
- Microfluidics with SERS substrates
- SERS on paper
- Plasmonic biosensors
- Synthesis of metallic nanoparticles with morphologies that can provide a high density of hot-spots
- Cleaning procedures to remove capping agents from nanoparticles
- Detection strategies for “non-resonant” molecules.
List of invited speakers:
- Miro Zeman (Photovoltaic Materials and Devices, Delft University of Technology, Netherlands)
- Matthias Karg (Physical Chemistry I, Heinrich-Heine-University Duesseldorf, Germany)
- Enzo di Fabrizio (KAUST - King Abdullah University of Science and Technology, Saudi Arabia)
- Thomas P White (Research School of Engineering, Australian National University, Australia)
- Rebecca Saive, (California Institute of Technology, Pasadena, CA, USA)
- Simion Astilean (Faculty of Physics, Babes-Bolyai University, Romania)
- Ivan Gordon (IMEC, Belgium)
- Pietro G. Gucciardi (CNR - Istituto Processi Chimico-Fisici, Italy)
- Katarzyna Siewerska, (School of Physics and CRANN, Trinity College Dublin, Ireland)
- Seweryn Morawiec, (Dipartimento di Fisica e Astronomia, Università di Catania, Italy)
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PV I : Hugo Aguas
Authors : M. Zeman, A. Ingenito, H. Tan, A. Smets and O. Isabella
Affiliations : Photovoltaic Materials and Devices, Delft University of Technology, Mekelweg 4, 2628 CD Delft, Netherlands
Resume : Effective light trapping in absorber layers enhances the efficiency of silicon-based solar cells. Recently, photonic and plasmonic structures have attracted a lot of attention as promising light-trapping structures. However, in practice, the best results in enhancing the light absorption in silicon-based solar cells were demonstrated by introducing rough surfaces that are built up by morphologies with different level of roughness. This approach is referred to as modulated surface textures (MST). The procedures to fabricate MST for both thin-film and crystalline silicon solar cells and their optical properties will be presented. A tandem thin-film silicon (TF-Si) solar cell with the highest initial efficiency of 14.8% will be presented. Among the crucial performance improvements was the application of a MST superstrate with micro-scale features in glass and nano-scale features in TCO layers. The nano-features scatter short-wavelength light into a thin amorphous silicon top absorber, while the micro-texture is responsible for the scattering of long-wavelength light into a nanocrystalline silicon bottom absorber. In crystalline silicon (c-Si) solar cells, especially in interdigitated back-contact configuration, the application of MST that consists of nano-cones formed on micro-pyramids minimizes the reflection losses and efficiently scatter light up to a wavelength that corresponds to the bandgap of c-Si. An interdigitated back-contacted (IBC) c-Si solar cell with MST at the front side exhibited a conversion efficiency of 19.8%, a record external quantum efficiency of 78% at short wavelengths, and electrical performance equal to the performance of the reference IBC device based on only front-side micro-pyramids.
Authors : O.Sanchez-Sobrado, M.J.Mendes, T. Mateus, A.Araujo, H. Aguas, E. Fortunato, R. Martins
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA
Resume : Photonic structures with wavelength-scale dimensions are highly promising for light trapping strategies applied to thin film photovoltaic (PV) devices. When applied on the front transparent contact of solar cells, optimally-shaped high-index dielectric structures can act as high-performing broadband anti-reflectors and scattering elements boosting the light absorption of the cell material along its photo-response spectrum. Exact electromagnetic computational optimization shave provided the best parameters of the structures and indicated that TiO2 is one of the most favorable materials . Therefore, in this work, we present an innovative nanosphere lithography method that allows the precise engineering of TiO2 wavelength-sized features with the distinct shapes and sizes appropriate for efficient light trapping in different thin film PV devices. This is a simple, low-cost and scalable approach consisting in 4 main steps: 1) deposition of periodic close-packed arrays of spherical polystyrene (PS) particles which act as the mask, 2) shaping the particles and increasing their spacing by O2 dry etching, 3) infiltration of TiO2 in the inter-particles spacing and 4) removal of the PS particles to leave only the structured TiO2layer. The morphology and optical properties (diffused transmission) of the nanostructures were characterized to optimize the best light trapping configuration.The results have been compared with the numerical calculations  which predict a notorious enhancement (up to 50%) of the solar cells efficiency, relative to devices with standard light trapping schemes. [1) Design of optimized wave-optical spheroidal nanostructures for photonic-enhanced solar cells. Accepted in NanoEnergy (2016)
PV II : Miro Zeman
Authors : Matthias Karg
Affiliations : Physical Chemistry I, Heinrich-Heine-University Duesseldorf, Universitaetsstr. 1, 40204 Duesseldorf, Germany
Resume : Organized nanoscale structures that can guide or manipulate the propagation of electromagnetic fields at optical frequencies are of great importance for applications in sensing, all-optical computing and photovoltaics. Typically fabricated by lithographic approaches, the realization of structurally defined, optically functional superstructures through bottom-up assembly of colloids remains challenging. Here, we present our latest results of using wet-chemically synthesized colloids with plasmonic nanoparticle cores and soft hydrogel shells for the fabrication of organized nanostructures that show collective optical effects. Assembly at the air/water interface is used as a powerful means to create plasmonic monolayers that homogeneously cover application-relevant areas and possess large single crystalline domains. We show how the inter-particle distance can be controlled by the soft hydrogel shell giving access to photonically relevant length scales. Long-range dipolar plasmon resonance coupling is observed for assemblies with extraordinarily high degrees of order. Manipulation of the surrounding refractive index matrix enhances the coupling strength significantly leading to pronounced surface lattice resonances that result from crossing-avoidance with the Bragg mode. Simulations based on finite difference time domain calculations are used to support our findings. References  A. Rauh, T. Honold, M. Karg, Colloid Polym Sci, 2015, 294, 37.  T. Honold, K. Volk, A. Rauh, J.P.S. Fitzgerald, M. Karg, J. Mater. Chem. C, 2015, 3, 11449.  K. Volk, J.P.S. Fitzgerald, M. Retsch, M. Karg, Adv. Mater., 2015, 27, 7332.
Authors : Kyunghwan Kim, Yunwon Song, Jungwoo Oh
Affiliations : School of Integrated Technology, Yonsei University, Yonsei Institute of Convergence Technology, 85 Songdogwahak-ro, Yeonsu-gu, Incheon, 21983, Republic of Korea
Resume : Surface texturing is one of the useful anti-reflection technologies for enhancing the performance of Si photovoltaic devices. Superior optical properties of GaAs fabricate high performance solar cells after hetero-integration with relevant materials. However, surface texturing has been a challenging issue due to ion induced plasma damage after dry etching of GaAs in complex vacuum system and nanolithography. In this work, we demonstrate inverted pyramid surface texturing using an-isotropic wet etching and metal-assisted chemical etching of GaAs. Nano-scale holes were embedded on micro-scale wave arrays using thermally agglomerated Au nanoparticle as catalysts for chemical etching. The average reflectance of micro/nano dual scale patterned GaAs is 14.4% in the wavelength range of 200–800nm which is lower than that of bare GaAs (52.2%), micro-scale wave patterned GaAs (31.9%), nano-scale hole patterned GaAs (31.4%). To our knowledge, this is the first demonstration that reduces the surface reflection by micro/nano dual scale structure using anisotropic wet etching of GaAs. Dual surface texturing fabricated by solely wet chemical etching improves the reflectance properties of optoelectronic devices and potentially reduce processing cost as an alternative to reactive ion etching and e-beam lithography.
Authors : Mustafa Ünal(1),(2)*, Zeynep Demircioğlu(1),(2), Ergi Dönerçark(1),(2), Engin Özkol(2), Raşit Turan(1),(2)
Affiliations : Department of Physics, Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey, The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey; Department of Physics, Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey, The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey; The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey; Department of Physics, Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey, The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Dumlupinar Blvrd no: 1, 06800, Ankara Turkey
Resume : Thin film solar cells have potential to decrease the cost of solar electricity. Obtaining minimum thickness or high efficiency in thin film solar cells is possible by applying efficient light trapping scheme. Scattering from different interfaces increase optical path length in absorber layer, which results with increase in absorption. Lately, texturing of glass/TCO interface gained importance. Aluminum induced texturing (AIT) is one of the many glass texturing methods. AIT gives the opportunity to control the size and distribution of micro- and nano-textures. There are various parameters affecting resultant texture such as glass type, aluminum thickness, annealing temperature, etchants, etc. AIT method can be combined with different texturing methods to obtain more efficient scattering. In this study, we have used macro-sized textured glasses, which are ?i?ecam Prism and Sandy Solar Glasses. These two glasses are textured with AIT method. Obtained surface texture is examined by SEM and optically characterized. By making a-Si:H solar cell on top of the textured side, effect of texture on efficiency is examined.
Authors : C. Mennucci,1 M.C. Giordano,1 D. Repetto,1 C. Martella, L. Mercaldo,2 I.Usatii,2 Delli Veneri,2 F. Buatier De Mongeot,1
Affiliations : 1 University of Genova, Department of Physics, Genova, 16146, Italy; 2 ENEA Portici research center, Napoli, 80055, Italy
Resume : Here we report on self-organised nanopatterning of substrates in view of light trapping and photon harvesting applications in thin film PV devices. Pseudo-periodic nanoscale features with a characteristic lateral size in the range of 200-600 nm and a root-mean-square roughness (σ) of the surface in the range of 150nm are formed over large areas (cm^2) recurring to single-step maskless approach based on defocused Ion Beam Sputtering (IBS). These high aspect ratio features confer both broadband light scattering and anti-reflective functionalities in the Visible and Near Infra-Red spectrum to glass and TCO substrates, as well as to crystalline semiconductor substrates like GaAs and Si. These light trapping potentialities, assessed by angle integrated scattering measurements, have been correlated to morphological parameters of nanostructured templates measured by AFM in view of photon harvesting optimization in PV devices. Thin film amorphous silicon solar cells (p–i–n single junctions) grown on nano-patterned glass superstrates showed relative enhancements in photon absorption exceeding 40% and in photocurrent exceeding 15% with respect to reference flat devices under standard AM1.5g conditions.
SERS I : Marc Lamy de la Chapelle
Authors : Enzo Di Fabrizio
Affiliations : KAUST ( King Abdullah University of Science and Technology) PSE - Physical Science and Engineering Division Thuwal Saudi Arabia
Resume : Recent advances in Nanoscience allow the realization of devices able to spatially confine the electric field at the surface of a noble metal and enhance it by several orders of magnitude. Conduction electrons at a metal-dielectric interface can be excited by incident light into an extended surface electronic state, called Surface Plasmon Polariton (SPP), once momentum constraints have been released. During the lecture it will be presented selected topics from our research activity. In particular it will be highlighted the results on single molecule detection, Plasmon Polariton conversion to Hot electrons  and a final application on Self-similar Ag-nanosphere based plasmonic devices, fabricated using e-beam and electroless techniques, for characterization of complex mixtures of bio-molecules. Major novelty resides in combined use of micro and nano-structures. The common aspects between the presented devices, is the design and the good and detailed control of the fabrication of the nanostructures, whose reproducible performances allows the identification of peptides content and state in the single molecule regime .  Nanoscale chemical mapping using three-dimensional adiabatic compression of surface plasmon polaritons F. De Angelis, et al. Nature nanotechnology 5 (1), 67-72, 2009  Hot-electron nanoscopy using adiabatic compression of surface plasmons A Giugni, et al, Nature nanotechnology 8 (11), 845-852,2013  Detection of single amino acid mutation in human breast cancer by disordered plasmonic self-similar chain ML Coluccio et al. Science Advances 1 (8), e1500487, 2015
Authors : M.C. Giordano 1, A. Foti 2, C. Mennucci 1, D. Repetto 1, D. Comoretto 3, P. Gucciardi 2, and F. Buatier de Mongeot 1
Affiliations : 1 Department of Physics, University of Genova, Via Dodecaneso 33, I-16146, Genova, Italy. 2 CNR IPCF Institute for Chemical and Physical processes, Viale F. S. D’Alcontres 37, I-98156 Messina, Italy. 3 Department of Chemistry, University of Genova, Via Dodecaneso 30, I-16146, Genova, Italy.
Resume : Highly ordered arrays of plasmonic nanostructures are confined on transparent nanopatterned templates by exploiting self-organized approaches. Two-dimensional arrays of gold nanostructures shaped as half-moon nanocrescents are prepared by glancing angle Au deposition on monolayers of polymeric nanospheres. Such arrays support dichroic excitation of Localized Surface Plasmon resonances, easily tunable into the Visible and Near Infra-Red spectrum by simply changing the nanocrescent morphological aspect ratio. The plasmonic response of nanocrescents has been tailored in order to maximize their efficiency as optical nanoantennas in Surface Enhanced Raman Scattering (SERS). Remarkably the Raman signal is amplified by three orders of magnitude with respect to a flat reference Au film, over large cm^2 areas. We achieve an effective tailoring of the SERS amplification by changing the nanocrescents shape as well as the density of satellite nanoclusters that decorate the border of each connected crescent. Nanocrescent arrays also behave as plasmonic metamaterials, enhancing the sensitivity in non-linear Optical Spectroscopies. A variance of this self-organized approach can also be applied to rippled glass templates, confining one-dimensional Au nanowire arrays endowed with strongly anisotropic plasmonic functionalities. References Robbiano et al. Adv.Opt.Mater. 1, 389, 2013. Giordano et al. ACS Appl.Mater.Interfaces 8,6629,2016. Belardini et al. Adv.Opt.Mater. 2.3: 208, 2014.
Authors : Raymond Gillibert (1 2), Florent Colas (1 3), Michael Canva (4 5), Marc Lamy de la Chapelle (1)
Affiliations : (1) Université Paris 13, Sorbonne Paris Cité, Laboratoire CSPBAT, CNRS UMR 7244, Bobigny, France; (2) HORIBA Jobin Yvon S.A.S. Villeneuve d'Ascq, 231 rue de Lille 59650 Lille, France; (3) Laboratoire Détection, Capteurs et Mesures, Centre Bretagne ZI de la pointe du Diable CS10070-29280 Plouzané; (4) Institut d'Optique Graduate School, Laboratoire Charles Fabry CNRS UMR 8501, Palaiseau, France; (5) Université de Sherbrooke, Laboratoire Nanotechnologies Nanosystèmes, LN2, UMI CNRS 3463, 3IT. Qc Canada;
Resume : Recent plasmonic studies have been performed on aluminium nanostructures, indicating a potential for surface enhanced Raman scattering applications. Because the real part of the permittivity is strongly negative, making possible to have a plasmon resonance from ultra-violet to near infra-red, the aluminium appears to be usable for enhanced spectroscopy in a very large wavelength range. Plasmonic properties and SERS were investigated already. However, no systematical SERS study was performed. In this study, plasmonic and surface enhancement Raman scattering (SERS) studies have been performed on aluminium nanodisks arrays of different diameters, which featured sharps localised plasmon resonance peaks ranging from the blue to the red, covering the entire visible spectrum. Raman spectra were acquired on all sizes of nanodisks with a red and near infra-red lasers, and the SERS intensity was quantified. In this study it is demonstrated that with such red lasers, only very small enhancement is observed. Discrete dipole approximation (DDA) simulations were equally performed and are in good agreement with the experiments. Sample stability was also tested and showed that the aluminium sample can be kept for a few months with small oxidation and thus that it might have practical applications for sensing in the future.
Authors : Damien Eschimese,a,b,* Steve Arscott,a Gaetan Leveque,a Thierry Melin,a Francois Vaurette,a Joachim Schreiber,b Philippe de Bettignies,b Marc Chaigneau,b
Affiliations : aInstitut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN), CNRS UMR8520, The University of Lille, Cité Scientifique, Avenue Poincaré, 59652 Villeneuve d'Ascq, France bHORIBA Jobin Yvon SAS Villeneuve d'Ascq Office, 231 rue de Lille, 59650 Villeneuve d’Ascq France
Resume : We present modelling, fabrication and characterization of atomic force microscopy-tip enhancement Raman spectroscopy (AFM–TERS) probes which demonstrate a very high electromagnetic (EM) enhancement due to a novel metallic nanocone/nanodisk combination at the tip apex. Calculations of the EM enhancement are obtained by finite element methods to improve the understanding of underlying physical phenomena and processes in the near-field and far-field optics. In addition, to the known ‘lightning rod effect’ and plasmonic resonance properties of a bulk metal tip, we study the cavity resonance modes of surface plasmons related to the dimensions of the metal part of the tip. We demonstrate advantages an original metallic nano-antenna at the apex rather than a full metallic system. We also highlight the importance of the radiative losses at the metal-dielectric interface that has motivated us to propose a particular shape of the apex which greatly improves the EM enhancement with a precise control of the spectral position of the optical response as a function of the nano-antenna dimensions, shape and material composition. The cantilever-based probes were fabricated using top-down micro/nanotechnology to enable many probes to be fabricated on single silicon wafers. Dark-field microscopy combined with a total internal reflexion excitation is used to characterize the optical properties of the localized EM enhancement in order to compare with the predictions of the numerical calculations. Compatible with a standard AFM cantilever mounting, the microfabricated AFM-TERS probes are novel high-performance optical near-field elements that will enable a powerful optical analysis and imaging technique for high resolution Raman microscopy.
PV III : Matthias Karg
Authors : Thomas P White, The Duong, Dale Grant, Daniel A Jacobs, Klaus J Weber and Kylie R Catchpole
Affiliations : Research School of Engineering, Australian National University, Canberra, 2601 Australia.
Resume : The rapid rise of perovskite solar cells to efficiencies beyond 20% presents an exciting opportunity for low-cost perovskite-silicon tandem cells with efficiencies exceeding the current crystalline silicon cell record of 25.6%, and potential efficiencies above 30%. Optimization of tandems requires detailed knowledge and characterization of the optical and electrical properties of every layer, as well as practical constraints imposed by processing sequences and chemical incompatibilities. This presentation will review the material and cell performance requirements to achieve high-efficiency perovskite-silicon tandem cells, with a particular focus on light management and optical design issues. In particular, it will discuss the modelling, analysis and experimental demonstration of a 20.2% efficient stacked 4-terminal tandem cell, and a 23.2% filter-less spectral-splitting tandem using CH3NH3PbI3 perovskite top cells and crystalline silicon bottom cells. We will also present recent modelling results for 2-terminal monolithic perovskite-silicon tandems and identify the key optical design challenges for these cells. Finally, we will review our recent analysis of transparent electrode requirements for thin film cells, and discuss the implications for the design of nanostructured metallic electrodes based on nanowires and nanogrids.
Authors : José V. Anguita1, Muhammad Ahmad1, Jeremy Allam1, Sajad Haq2 and S. Ravi P. Silva1*
Affiliations : 1Advanced Technology Institute (ATI), University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom. 2QinetiQ, Cody Technology Park, Ively Road, Farnborough, GU14 0LX, United Kingdom.
Resume : The development of techniques to couple light into novel forms of carbon such as graphene, is crucial to allow the exploitation of their potential optoelectronic properties. Despite graphene’s ability to absorb light, broadband optical coupling into such thin material is challenging, and remains mostly blind to light, as it is only able to absorb ~ 2.3% of the light that is incident on it. This low absorption currently hinders the optoelectronic potential of graphene. To unlock this potential, it is necessary to develop the technologies for broadband optical coupling. Here, we have learned from nature (the eye of the moth) to develop technologies for enhancing this coupling. Our results show a few-layer absorber of decoupled graphene (totaling only15nm thin) within our disordered moth-eye structures feature an absorption from 95-99% over an ultra-broadband range, spanning from the mid-IR to the UV. Our growth technologies is large-area compatible, and allow graphene growth at low substrate-temperatures, allowing compatibility with current semiconductor processing lines.
Authors : Michael Vetter, Guobin Jia, Gudrun Andrä
Affiliations : Leibniz-Institute of Photonic Technology, Jena, Germany
Resume : Liquid-phase crystallized silicon on glass (LPCSG) via line-focus laser beam is a promising way to fabricate high-quality polycrystalline silicon (Si) solar cell absorbers. Solar cell efficiency over 12% has been achieved in about 10 um thick LPCSG absorbers with short current densities (Isc) of nearly 30 mA/cm2 by introducing light trapping (LT) structures at front and backside of the solar cell . The impact of conventional pyramidal LT structures has been studied in detail . LT at the glass Si interface reducing reflection losses and increasing the optical path length in the absorber is most important for improved quantum efficiency in UV and visible wavelength range. Texturing at the Si back side and a high efficient back reflector is necessary to improve the absorption of light in the long wavelength range. However, texturing increases the surface of the solar cell resulting in enhanced surface recombination velocity which decreases effective carrier diffusion length and carrier collection efficiency. Therefore, a careful trade-off between dimensions of surface structure and respective surface recombination velocity has to be done for optimizing these thin film devices. Nanowire structuring at the solar cell back side is an alternative method to conventional texture to provide an effective light trapping in LPCSG absorbers . In this work we compare different LT structures in LPCSG absorber prepared by conventional texturing and nanowire structuring of Si. The impact of LT structures on Isc is determined from optical measurements on LPCSG absorbers in combination with typical spectral response of LPCSG absorbers. The impact of texturing on surface recombination and open circuit voltage is determined from effective carrier lifetime data determined in LPCSG absorbers . T. Frijnts et al., Sol. Energy Mater. Sol. Cells 143 (2015) 457  M.Z. Pakhhuruddin et al., IEEE J. Photovolt. 80 (2016) 159  G. Jia et al., Sol. Energy Mater. Sol. Cells 126 (2014) 62  M. Vetter et al., Energy Procedia (2016) accepted for publication
Authors : E. Messina1, A. Foti1, G. Di Marco1, C. Riccucci2, G. Di Carlo2, O. M. Maragò1, B. Fazio1, G. M. Ingo2, C. Vasi1 and P. G. Gucciardi1
Affiliations : 1 CNR-IPCF, Viale F. Stagno D'Alcontres 37, 98158 Messina, Italy 2 CNR-ISMN, Area della Ricerca RM1-Montelibretti, I-00016 Monterotondo Scalo, Rome, Italy
Resume : Electrical conductive adhesives (ECAs) are polymeric resins filled with micro and nanostructured metal particles. ECAs show up as viscous pastes that can be molded into any desired shape and become rigid after curing. Here we show that silver-filled ECAs can be used as efficient SERS substrates. To this aim we have developed a procedure to remove the polymeric layer covering the silver platelets and to shape ECAs into different forms, from thin films to micrometric swabs. ECAs SERS substrates are used to detect molecules dispersed in solution, reaching a sensitivity down to 1 pM, and, as swabs, to detect traces of chemicals from solid surfaces and dyes absorbed on paper. Application examples are shown in the fields of culturale heritage preservation (pigment identification), security (explosives detection), forensics (inks analysis).
Poster Session 1 : Thomas White
Authors : Kateryna Kazanovska,Sergiy Lushpenko, Aleksey Pashchenko
Affiliations : The A. N. Podgorny Institute for Mechanical Engineering Problems at NAS of Ukraine, Kharkiv; Donetsk Physic-Technical Institute at the NAS of Ukraine Kyiv,
Resume : The solar daily energy receipt in a collector is defined as the time integral of product of the insolation (energy density) and the angle cosine between the sun direction and the normal of the collector surface with integration limits that stand for sunrise and sunset moments. The insolation has been approximated by 4th degree polynomial for simplification as it is a function of the angular height of the sun and given discretely in the literature. The angular height is calculated as a function of latitude of the collector location, angle of the sun declination and the sun offset angle relative to its noon position. The angle cosine between the sun direction and the normal of the collector surface is a function of latitude, azimuth angle of the receiving collector plane, which is usually equal to zero as the collector is southward, and the tilt angle of the receiving collector surface relative to the horizontal plane that is traditionally chosen to be equal to the latitude. The distribution function depending on the tilt angle based on the latitude is obtained. Search results for optimal tilt angle of the flat solar collector were obtained in the industrial center located in Ukraine, Kharkov, they showed that the increase of energy receipt is 21.44 ± 0.02% compared to the traditionally recommended tilt angle in the highest daytime, more than 8% for the first half of the year and almost 6.5% for the full year.
Authors : Katarzyna Grochowska(1), Mariusz Szkoda(2), Jakub Karczewski(3), Katarzyna Siuzdak(1)
Affiliations : (1) Center for Plasma and Laser Engineering, The Szewalski Institute of Fluid Flow Machinery, ul. Fiszera 14, 80-231 Gdansk, Poland; (2) Faculty of Chemistry, Gdansk University of Technology, Narutowicza 11/12, 80-233, Gdansk, Poland; (3) Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland
Resume : Titanium dioxide nanotubes (TiO2 NT) have gained a lot of interest in recent years as they can be widely used in a variety of industrial applications like photovoltaics, catalysis, filtration, sensing or in drug delivery systems. Here, we show that TiO2 NT covered with thermally treated gold layers exhibit improved sensing properties especially in terms of Surface Enhanced Raman Spectroscopy (SERS). NT have been produced via anodization process of Ti foil in the presence of fluoride ions followed by calcination in 450°C to ensure the anatase crystalline phase. The SEM inspection confirmed that obtained structures are composed of well-aligned and highly ordered nanotubes of average length of 200 nm and internal diameter of 70 nm. Subsequently, gold layers of thickness from ultrathin (5 nm) up to 200 nm have been deposited onto prepared TiO2 substrates by magnetron sputtering technique. The as deposited Au films were then thermally dewetted in the furnace (< 500°C) in ambient atmosphere and the formation of Au nanoparticles/islands has been observed by means of SEM imaging. It has been found that for the TiO2 NT covered with heat-treated Au layers the measured average SERS signal is markedly higher than the one observed for bare as well as for non-treated Au decorated titania nanotubes. The obtained results confirm that prepared material can be used as SERS substrate. KG and KS acknowledge the NCN for financial support via grants 2012/07/N/ST5/02139 and 2012/07/D/ST5/02269.
Authors : Mindaugas Kamarauskas, Vladimir Agafonov, Virginijus Bukauskas, Marius Treideris, Audruzis Mironas, Arunas Setkus
Affiliations : Center for Physical Sciences and Technology, Sauletekio ave 3., LT-10257, Vilnius, Lithuania
Resume : Technology of the intentionally textured surfaces are frequently applied not simply for tuning of the optical reflectance of the components in the photonic systems but also for formation of functional layers with specific micro and nano structures. Metal catalyst assisted etching is known to be a cheap and flexible technology that can be adapted for the surface modification in various practical applications. However, the methods and conditions acceptable for controlling the process flow still require better description and understanding. In addition, there is a great demand for reduction of the process costs in the practical applications because the metal assisted etching is typically based on the reaction between Si and HF:H2O:H2O2 solution in the presence of noble metal catalyst. In this work we investigate the nickel assisted etching of Si surfaces. We intentionally formed deep structures and analyzed the dependencies of geometrical characteristics on the conditions of the technological processes. In our study we varied the amount of Ni catalyst, composition of the etching solution, the electrical current and the duration of etching. The relationship between these conditions and the surface structure was described in terms of the characteristics of the surface arrangement obtained experimentally from scanning modes of the atomic force microscopy. The possibilities to optimize the conditions are discussed.
Authors : Jafar Poursafar, Mohammad Bashirpour, Mohammadreza Kolahdouz*, Ebrahim Asl-Soleimani, Abbas Rostami
Affiliations : ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran Email: Kolahdouz@ut.ac.ir
Resume : The photovoltaic devices suffer from two major problems; one is the low conversion efficiencies and the other one is the high production costs. Materials and processing represent a large fraction of the expenses. About 40% of the ﬁnal module price in bulk crystalline silicon solar cells, comes from the silicon materials and its processing costs. Recently, thin ﬁlm solar cells with an active layer thickness of about 1 to 2 μm are desired as a way to reduce the material costs. However, one disadvantage of all thin ﬁlm solar cells is their week absorption at the wavelengths near to the electronic bandgap of the semiconductor, due to the reduced absorber thickness. Therefore, light trapping schemes are required for the design of ultrathin solar cells to enhance light absorption. We have proposed a tandem ultra-thin silicon solar cell, in which each layer is integrated by metal nanostructures. The Si layers are disconnected via SiO2 layer with embedded Ag strips. The surface of the top Si layer and the bottom of the underneath Si layer are connected to each other using contacts of Ag periodic array nanostructure. The obtained results have demonstrated that the proposed structure has synergistic effect on light absorption and gives rise to 172% light absorption enhancement and 139% short-circuit current density enhancement over the whole usable solar spectrum, compared to the one layer bared structure.
Authors : M. J. Mendes, O. Sanchez-Sobrado, A. Araújo, A. Vicente, A. Lyubchyk, T. Mateus, H. Águas, E. Fortunato, R. Martins
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal
Resume : The regime of wave optics is challenging to model but is highly promising for light management in non-wafer-based photovoltaics. Several strategies have been proposed employing the anti-reflection and forward scattering properties of high-index dielectric scatterers patterned on the illuminated face of solar cells to boost their optical thickness (absorption) while reducing the physical thickness of the thin absorber. This work numerically investigates a novel class of nanophotonic structures with generalized spheroidal geometries whose parameters are optimized, employing FDTD computations, for application in amorphous and crystalline thin film silicon solar cells. The optical elements were designed to maximize the broadband absorption in fully-planar silicon layers, thereby preventing the increase of carrier recombination (caused by higher surface area) due to their implementation. The best structures, composed of high-index (TiO2) half-spheroids, yield high photocurrent values (up to 32.5 mA/cm2) which are almost 3 times above those attained in practice with the conventional cell technology. Therefore, a notorious enhancement (up to 50%) of the cells efficiency is predicted, relative to standard light trapping schemes (optimized single-layer anti-reflection coatings). These results set the state-of-the-art closer to the theoretical light trapping limit of Lambertian surfaces in the geometrical optics regime.
Authors : Andreia Araújo,* Manuel J. Mendes, Tiago Mateus, António Vicente, Daniela Nunes, Tomas Calmeiro, Elvira Fortunato, Hugo Águas* and Rodrigo Martins*
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal
Resume : The plasmonic scattering properties of metal nanoparticles are of great interest for light trapping in photovoltaics. In most cases, the nanoparticles are self-assembled by solid-state dewetting over a transparent conductive oxide (TCO) layer of the cells structure. Up to now, this process has been optimized mainly by tuning the thermal annealing parameters responsible for dewetting, or the thickness of the precursor metallic layer; but little attention has been paid to the influence of the underlying TCO layer on the morphology of the nanoparticles formed, which is the focus of the present article. This work investigates Ag nanoparticles structures produced on distinct surfaces by a simple, fast and highly reproducible method employing rapid thermal annealing. The results indicate that the thermal conductivity and surface roughness of the TCO layer are key factors that allow controlling the morphology of the resulting nanostructures. In particular, we demonstrate that parasitic absorption is reduced and scattering is pronouncedly enhanced by forming Ag nanoparticles on a thin (30 nm) AZO film with good conductivity and low surface roughness (~1 nm). These results unveil novel possibilities for the improvement of plasmonic nanostructures fabricated by thermal dewetting, via the careful adjustment of the physical properties of the underlying surface.
Authors : a Jin-Young Choi, b Chaehyun Kim, a Pil-Hoon Jung, a Hak-Jong Choi, ab Heon Lee
Affiliations : a Department of Materials Science and Engineering, Korea University, Seoul, South Korea; b Institute for Converging Technology, Korea University, Seoul, South Korea
Resume : One-dimensional ordered TiO2 nanotube (TNT) arrays obtained by electrochemical anodization of Ti foil in fluoride-based ethylene glycol have attracted great attention for use as photoelectrode in photoelectrochemical (PEC) water splitting. TiO2 is known to be a favorable material for PEC water splitting due to its high photo-stability, non-toxicity, and relatively low cost. 1D nanostructures can provide high electron mobility and high surface area, which are essential properties for efficient PEC water splitting. Especially, TNT arrays are possible to maximize their surface area for high efficiency of PCE water splitting. However, vertically oriented TNT arrays are difficult to be fabricated because of the collapse of TNT arrays caused from roughen surface of titanium foil. In addition, one of the drawbacks of TNT arrays on Ti foil is the occurrence of peeling and/or cracking of TNT arrays during the high temperature annealing process due to the large strain between TiO2 and Ti, which is detrimental to the PEC water splitting performance. In this study, we fabricated the vertically oriented TNT arrays to use as photoelectrode of PEC water splitting. In order to fabricate the vertically oriented TNT arrays, Ti foil was anodized using 2 step process composed in order of smoothening of Ti foil and formation of TNT arrays. First, Ti foil was anodized to form randomly oriented TNT arrays. Then, randomly oriented TNT arrays were removed using immersion of sulfuric acid with ultrasonic treatment. Next, smoothen Ti foil was re-anodized to form vertically oriented TNT arrays with amorphous phase. In order to transform from amorphous TiO2 to anatase TiO2, vertically oriented TNT arrays were annealed at optimized condition. After that, vertically oriented TNT arrays with anatase phase were investigated for morphological, optical and structural properties using various measurement system such as field-emission scanning electron microscopy (FE-SEM), UV-vis spectroscopy and X-ray diffraction (XRD) goniometer,. The efficiencies of PEC water splitting were measured for different length, pore size and annealing condition of TNT arrays using solar simulator, and incident photon-to-current efficiency (IPCE) measurement. In these results, optimized condition for TNT arrays was derived which has a photocurrent of 0.75 mA at 1.23 V versus the reversible hydrogen electrode (RHE) approaching to theoretical maximum. Therefore, we demonstrate the highly efficient photoelectrode using vertically oriented TNT arrays, which is applicable in the fields of solar energy conversion such as dye-sensitized solar cell, perovskite solar cell, photocatalyst and photoelectrochemical water splitting.
Authors : Maria João Oliveira, Pedro Quaresma, Andreia Araújo, Eulália Pereira, Ricardo Franco, Elvira Fortunato, Rodrigo Martins, Hugo Águas
Affiliations : i3N/CENIMAT, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal REQUIMTE/UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal REQUIMTE/UCIBIO, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal
Resume : Surface Enhanced Raman Spectroscopy (SERS) is a powerful spectroscopic technique, based on light dispersion by Raman-active molecules in the vicinity of plasmonic metal nanostructures. The major advantage of the technique is that is capable of detecting trace amounts of chemicals and identifying them based on their unique vibrational characteristics. The objective of this work is to explore the feasibility of SERS as a robust and fast technique for analytical applications in portable sensors. Using paper as solid support, SERS substrates were produced by deposition of solutions containing spherical silver nanoparticles (AgNPs) or star-shaped silver nanoparticles (AgNSs), in wells enclosed by hydrophobic barriers in two different types of paper: with high porosity (Whatman no.1) and with low porosity (office paper). , SERS efficiency of these modified paper substrates was tested using rhodamine-6G- a model dye for SERS ? and a 633 nm laser. By depositing nanoparticles from solution, both papers showed no paper-derived fluorescence, a general problem reported for Raman measurements. The greater retention of nanoparticles on its surface highlighted office paper as an efficient SERS substrate. The AgNSs-office paper SERS substrate allowed an enhancement factor (EF) of 106, a result in the same order of magnitude as the EF obtained for paper surfaces screen-printed with AgNPs, a more expensive production process. This same substrate could achieved a limit of detection of 0.17 ppb for R6G and proved that they could be reproducible over 5 weeks of measurements. Studies are underway with these promising paper-based substrates to expand the work to relevant analytical molecules such as food contaminants. References  S. Schlücker, Angew. Chem. Int. Ed. Engl., 19 (2014). pp. 4756?95  N. G. Bastús, F. Merkoçi, J. Piella, and V. Puntes, Chem. Mater., 26 (2014), pp. 2836?2846.  A. Garcia-Leis, J. V. Garcia-Ramos, and S. Sanchez-Cortes, J. Phys. Chem. C, 117 (2013), pp. 7791?7795.  L.-L. Qu, Q. Song, Y. Li, M. Peng, D. Li, L. Chen, J. S. Fossey, and Y. Long, Anal. Chim. Acta, vol. 792 (2013), pp. 86?92.
Authors : M. Smeets1, K. Wilken1, H. Aguas2, L. Pereira2, E. Fortunato2, R. Martins2, V. Smirnov1,*
Affiliations : 1Forschungszentrum Jülich GmbH, IEK-5 Photovoltaik, Jülich, Germany 2 CENIMAT/I3N, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, FCT, Universidade NOVA de Lisboa and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
Resume : We present the development of light management schemes for flexible solar cells on paper substrates. These flexible paper substrates, being extremely lightweight and unexpensive, implies additional requirements on the functional layers of the solar cell, particularly more strict limitations in the process temperature range and sensitivity of the paper substrates to various process solvents. These requirements restrict the range of available light trapping approaches as well as a choice of Transparent Conducting Oxide (TCO) materials. In this work, UV nanoimprint process is applied to texture flexible paper substrates for light trapping in solar cells. The random texture on the substrate was obtained by replicating a texture of high temperature magnetron sputtered and wet chemically etched ZnO:Al with optimized light scattering morphology. The morphology and light scattering properties of nanoimprinted paper substrates were evaluated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Haze and Angular Resolved Scattering (ARS) measurements. Our results demonstrate that by using nanoimprint technology, we have successfully replicated optimized light trapping textures of etched high temperature ZnO:Al, leading to a significantly improved ARS curves (mainly for the scattering angles below 50°). Prototype thin film silicon solar cells fabricated on paper substrates demonstrate an improvement in the short-circuit current density from 11.4 mA/cm2 to 13.6 mA/cm2, resulting in an improvement in conversion efficiency by 1% (absolute).
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PV IV : Ivan Gordon
Authors : Rebecca Saive1, Colton R. Bukowsky1, Sisir Yalamanchili1, Mathieu Boccard2, Theresa Saenz1, Aleca M. Borsuk1, Zachary Holman2, Harry A. Atwater1
Affiliations : 1 California Institute of Technology, Pasadena, CA, USA; 2 Arizona State University, Tempe, AZ, USA
Resume : The supply of clean, renewable energy is the most important step towards preventing climate change. Photovoltaic devices can convert the abundant power of the sun into electrical energy and thus, deliver carbon dioxide emission free energy. Increasing the efficiency of solar cells will decrease the cost of electricity generated by photovoltaic power plants and lead to economically profitable large scale application. Improving state of the art solar cells requires optimal photon management. This talk will give an overview of different strategies for photon managements pursued in the Atwater research group and present the advances achieved in the field of effectively transparent contacts. A significant portion of the incoming photons is lost at the front contacts of solar cell due to parasitic absorption within the transparent conductive oxide or reflection at contact grid fingers. Better transparency usually leads to deteriorate conductivity which in turn leads to electrical losses in the solar cell. We designed a new contact principle that overcomes shadowing losses and parasitic absorption without decrementing the conductivity. By redirecting the light to the active area of the solar cell micro-scale triangular cross-section grid fingers (ETCs) achieve a measured transparency of up to 99.9 %. Due to their close spacing (around 100 µm) ETCs can replace grid fingers as well as transparent conductive oxides (TCO). We show in simulations and experiments that ETCs can increase the short circuit density in solar cells by around 6 % without discriminating the fill factor.
Authors : Yunwon Song, Kyunghwan Kim, Jungwoo Oh
Affiliations : School of Integrated Technology, Yonsei University, Yonsei Institute of Convergence Technology, 85 Songdogwahak-ro, Yeonsu-gu, Incheon, 21983, Republic of Korea
Resume : Antireflective layers fabricated with subwavelength structures (SWSs) dramatically improve the performance of solar cells by gradually changing the refractive index at broad wavelengths. However, nanolithography techniques for fabrication of SWSs such as e-beam or laser interference lithography are very expensive, complex and not suitable for a large area. In this work, we fabricated Si SWSs of nanohole random arrays on Si substrates. To further reduction of the reflectance, micro-scale inverted pyramid pit arrays were first formed before the nanohole texturization. Nanoholes were formed onto these inverted pyramids by agglomeration of Au thin films and metal-assisted chemical etching (MacEtch) in H2O2/HF aqueous solution. MacEtch followed by metal agglomeration is a new cost-effective anisotropic etch processes. We optimized the feature size of SWSs by controlling agglomeration temperature and etching time. A significant reduction in the reflectance was acquired for 1.1mm height of SWSs. The specular reflectance, which is important for high quantum efficiency of solar cells in a wide angle of incidence, exhibited a strong dependency on the angle of incidence. Results showed that extremely low total reflectance of 2.9% and average reflectance of below 3.6% up to angle of incident of 60 degrees in the wavelength range of 200-1100nm. Si SWSs fabricated with metal-assisted chemical etching combined with metal agglomeration have dramatically improved the reflectance characteristics of antireflective layer with simple and low-cost processes.
Authors : Pil Hoon Jung, Yang-Doo Kim, Young hoon Sung, Hak-jong Choi, and Heon Lee
Affiliations : Department of Material Science and Engineering, Korea University
Resume : Silver nanowires (Ag NWs) technologies are promising conductive transparent electrodes for replacement of indium tin oxide (ITO) and fluorine-doped tin oxide (FTO). Above all, the junction of metallic nanowires has been an important issue in the bottom-up fabrication of organic solar cells s. Welding technologies are currently required to modulate the heating mechanism appropriately. In this study, microwave-assisted welding was introduced in order to improve the optical transmittance and electrical conductivity of Ag NWs in terms of simple, selective, and rapid processing. Besides, Ag NWs enhance the power conversion efficiency (PCE) of organic solar cell. Because, the Ag NWs absorb light strongly at the plasmon resonance condition. This method includes only two steps for fabricating Ag NWs electrodes. First, Ag NWs dispersed in a solvent were coated on polymer substrates using spin coating. Subsequently, the Ag NWs-coated substrates were exposed to microwave radiation for varying exposure times of 1 min, 2 min, and 3 min and the resulting optical transmittances and electrical conductivities are compared. To examine the suitability of thus welded Ag NWs for flexible substrate electrodes, bending tests were performed. Following these tests, we found that both the optical transmittance and electrical conductivity were preserved. Consequently, the sheet resistance was reduced by 40% and it could be shown that welded Ag NWs have good mechanical strength, even after bending test. The highly flexible and transparent electrodes can be mounted on any non-planar surfaces and applied for various for future flexible electronics.
Authors : Karen Wilken, Friedhelm Finger, Vladimir Smirnov
Affiliations : IEK-5 Photovoltaics, Forschungszentrum Jülich GmbH, Jülich, Germany
Resume : Flexible solar cells offer many advantages, such as high throughput production by roll-to-roll manufacturing, versatility regarding shapes and size, and also exceptionally light weight. To minimize costs of the device, flexible transparent polymer substrates such as polyethylene terephthalate (PET) is a convenient alternative. For these types of substrates, usually a barrier layer is necessary to prevent the diffusion of moisture and/or oxygen into the photovoltaic device. An important aspect to achieve high efficiencies in thin-film solar cells is the light management concept. Wet-chemical etching of aluminum doped zinc oxide (ZnO:Al) has been shown to result in light trapping textures that significantly enhance the device performance due to improvement in the short circuit current density. In this study, we investigate the wet-chemical etching and resulting light scattering properties of aluminum-doped zinc oxide, deposited at low temperature (< 140 °C) on PET substrates. Special emphasis is put on the influence of a thin (20 nm) barrier layer of zinc tin oxide (ZnSnOx) on subsequent growth and properties of ZnO:Al layers. We evaluate the electrical, optical and light scattering properties of ZnO:Al layers (textured by chemical etching in in 0.5 % HCl solution) grown on PET and PET/ZnSnOx substrates. Our results demonstrate that in the case of the PET/ZnSnOx substrate a homogeneous crater-like structure, suitable for light trapping in solar cells, evolves. In contrast, on bare PET substrates, the ZnO:Al layer etches rather inhomogeneously and partly completely down to the substrate, suggesting presence of cracks or voids in the bulk of ZnO:Al. We show that performance of amorphous silicon solar cells is significantly enhanced, when a ZnSnOx barrier layer is used, leading to an improvement in Jsc by 2.3 mA/cm² compared to a solar cell on bare PET substrate.
SERS II : Enzo Di Fabrizio
Authors : Simion Astilean, Monica Potara, Timea Simon, Sorina Suarasan, Sanda Boca-Farcau, Cosmin Farcau, Cosmin Leordean, Ana Gabudean, Monica Focsan, Dana Maniu, Monica Baia
Affiliations : Nanobiophotonics and Laser Microspectroscopy Center, Interdisciplinary Research Institute on Bio-Nano-Sciences Babes-Bolyai University, T. Laurian Str. 42, 400271, Cluj-Napoca, Romania; Department of Bimolecular Physics, Faculty of Physics, Babes-Bolyai University, M Kogalniceanu Str 1, 40084, Cluj-Napoca, Romania
Resume : In this presentation we give an overview of the current approaches we employ in our laboratory to fabricate plasmonic nanostructures exhibiting both spectroscopic versatility and bio-specificity toward implementation in nanomedicine. Firstly, a large variety of plasmonic nanostructures are fabricated on solid substrates (films) by using self- or template-assisted assembling of nanoparticles or nanoimprint lithography. The second route involves chemical synthesis of gold or silver nanoparticles of controlled size and shape (rods, prisms, stars-shaped) coated by biopolymer (chitosan, poly(ethylene) glycol, pluronic, gelatine) to provide both the right optical response and good biocompatibility. For instance a class of biocompatible “optically hot” nanoparticles are efficiently used for both spectroscopic intracellular investigation via SERS and plasmonic-induced hyperthermia. An interesting result represents the demonstration of gold nanorods acting as dual-modal spectroscopic enhancers in SERS and metal-enhanced fluorescence (MEF). Chitosan-coated triangular silver nanoparticles can operate as dual-modal sensors via surface plasmon resonance (LSPR) and SERS, both in solution and on solid substrate and perform intracellular imaging via SERS or trigger localized hyperthermia in tumors. Recently we demonstrate the multimodal activity of small aggregates of gold nanoparticles as both SERS and FLIM nanoprobes and drug delivery carriers. Currently we focus on development of SERS-based plasmonic nanoprobes conjugated to reporters and drugs to perform imaging, diagnostics and therapy (theranostics).
Authors : Raymond Gillibert (1 2), Mitradeep Sarkar (3) Jean François Bryche (3 4), Ryohei Yasukuni (1), Julien Moreau (3), Mondher Besbes (3), Grégory Barbillon (4), Bernard Bartenlian (4), Michael Canva (3 5) and Marc Lamy de la Chapelle (1)
Affiliations : (1) Université Paris 13, Sorbonne Paris Cité, Laboratoire CSPBAT, CNRS UMR 7244, Bobigny, France; (2) HORIBA Jobin Yvon S.A.S. Villeneuve d'Ascq, 231 rue de Lille 59650 Lille, France; (3) Institut d'Optique Graduate School, Laboratoire Charles Fabry CNRS UMR 8501, Palaiseau, France; (4) Université Paris-Sud, Institut d'Électronique Fondamentale CNRS UMR 8622, Orsay, France; (5) Université de Sherbrooke, Laboratoire Nanotechnologies Nanosystèmes, LN2, UMI CNRS 3463, 3IT. Qc Canada;
Resume : Plasmonic properties of gold nanostructures deposited on a dielectric substrate have been widely studied. However when the nanostructures are deposited on a gold film, the optical properties change drastically because of the propagation of the surface plasmon and its coupling with the grating and the localized plasmon resonance of the structure. We thus studied the far-field, with extinction measurements and near-field properties with SERS measurements of such substrate, and we compared them with the same structures deposited directly on an ITO substrate. We characterised them at different excitation wavelengths and by tilting the sample to excite different modes. First we demonstrate that the SERS intensity exhibits strong variation depending on the excitation angle and its maximum for specific angles corresponding to the excitation of Bragg modes. This result was confirmed by Finite elements method simulations. Second, we determine the localisation of the field enhancement by the addition of a silica cap on the top of the nanostructures to prevent the probe molecules to graft on this part of the structure. It was observed that for samples deposited on gold film, there is no difference in the SERS intensity between capped samples and uncapped ones. Indicating all the SERS signals comes from the sides of the nanodisks. However, in the case of ITO substrate, we can observe a decrease of more than half of an order of magnitude when the samples are capped with silica. This indicates that on those samples, most of the signal comes from the top of the nanostructures.
Authors : Kseniya Girel,Liubou Mikhnavets, Hanna Bandarenka, Vitaly Bondarenko
Affiliations : Belarusian State University of Informatics and Radioelectronics, Belarus
Resume : Surface enhanced Raman scattering (SERS) on plasmonic silver (Ag) surfaces with nanorough morphology is a phenomena providing an extremely sensitive Raman spectroscopic investigation of numerous biological compounds. However Ag nanostructures are known to demonstrate SERS-activity at the blue-green excitation wavelengths while red and near-IR ones are more preferable for the study of bioorganic species. This limitation is caused by the position of the surface plasmon resonance (SPR) band of Ag in the short wavelength range of the visible spectrum. In present work we report on fabrication and characterization of SERS substrates based on silvered macroporous silicon (macroPS) which can be used for the ultrasensitive detection of organic molecules at the excitation wavelengths varied in the visible and near-IR ranges. MacroPS was fabricated by anodization of p-Si wafer in a HF-based solution. The depth and diameter of the macropores altered from 500 to 1000 nm meeting the requirements for the dimensions of so-called plasmonic nanovoids. Thus further covering of macroPS with Ag by electroless deposition led to the formation of Ag nanovoids. The mechanism of the SPR broadening and SERS-signal increase due to surface plasmon mode of strong ring component in the area of pore entrance and contribution from multiple rays’ reflection inside the nanovoid is discussed. A detailed description of the Ag nanovoids and an interpretation of SERS spectra of different analytes are presented.
Authors : S. Gomez-Grana, Le Beulze, H.Gehan S. Mornet,S. Ravaine,M. Correa-Duarte, L. Guerrini, R.A. Alvarez-Puebla, E. Duguet, E. Pertreux, A. Crut, P.Maioli, F. Vallée, N. Del Fatti, O.Ersen, M. Treguer-Delapierre
Affiliations : CNRS, Univ. Bordeaux, ICMCB, UPR 9048, 33600 Pessac, France. firstname.lastname@example.org; CNRS, Univ. Bordeaux, CRPP, UPR 8641, 33600 Pessac, France. Departamento de Química Física, Biomedical Research Center (CINBIO), and Institute of Biomedical Resaerch of Ourense-Pontevedra-Vigo (IBI), Universidade de Vigo, Vigo, Spain. Medcom Advance SA. Viladecans Bussines Park, Edificio Brasil, C/Bertran i Musitu, 83-85, 08840. Universitat Rovira i Virgili. C/ Marcellí Domingo s/n, 43007 Tarragona, Spain. ICREA. Passeig Lluís Companys 23, 08010 Barcelona, Spain. Institut Lumière Matière, UMR5306 , Université Claude Bernard Lyon 1, CNRS
Resume : Raspberry-like nano-objects made of large plasmonic satellites (>20 nm) covering a central dielectric particles have many potential applications as photonic materials, superlenses as well as (bio-) sensing, but their synthesis remains challenging. Herein, we show, how to build a stable and robust raspberry-like nano-system with close-packed satellites, by combining monodisperse silica particles (80 and 100 nm) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10-50 nm). Their spectral characteristics (wavelength, linewidth, extinction cross-section) have been measured using the spatial modulation spectroscopy technique (SMS) and interpreted with a numerical model. The plasmonic nanostructures exhibit numerous hot spots at satellite junctions contributing to the excellent surface-enhanced Raman scattering (SERS) performance of the composite materials. The spectroscopic investigation indicates that the SERS efficiency is highly dependent on the dimension and nature of plasmonic satellites.
PV V : Rebecca Saive
Authors : Ivan Gordon, Twan Bearda, Valerie Depauw, Miha Filipic, Hariharsudan Sivaramakrishnan Radhakrishnan, Kris Van Nieuwenhuysen, Menglei Xu, Maarten Debucquoy
Affiliations : IMEC, Kapeldreef 75, 3001 Leuven, Belgium
Resume : In order to reduce the material cost for silicon solar cells, imec is investigating the feasibility of making cells on very thin monocrystalline silicon foils. We proposed in the past the so-called i2-module approach, which aims for module-level processing (many substrates in parallel) of thin silicon foils bonded to a large glass superstrate. The substrates used for this concept are high-quality epitaxial foils lifted off from a parent silicon substrate using porous silicon made by electrochemical etching. The porous silicon serves both as seed for epitaxy and as detachment layer. In this paper, we will show that by optimizing the porous silicon, we have managed to obtain 100μm thick silicon foils with effective lifetimes up to 1.3ms, and 40μm thick foils with effective lifetimes up to 700μs, both with high detachment yield. We will also review the current status of the process development for solar cells made from these thin foils. In a first approach, heterojunction solar cells are fabricated on freestanding epitaxial wafers of 40μm thickness. In a second approach, heterojunction back-contacted cells are fabricated on thin foils that are bonded to a glass superstrate. Challenges for device processing and limitations in cell performance will be discussed. Finally, we will show how nanophotonics can be used to improve the current density of the solar cells made from these thin silicon foils by nanotexturing the front surface of the foils.
Authors : Meftah TABLAOUI, Mourad DERBAL, Kheirreddine LEBBOU.
Affiliations : Centre de Recherche en Technologie des Semi-conducteurs pour l’Energétique Algiers, Algeria; LASICOM, Physics Dept., Blida1 University, Algeria; Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS.
Resume : The structural properties of Cu2ZnSn1-xGexS4 (CZTGS) bulk crystals prepared by solid state reaction have been investigated by means of X-ray diffraction. Depending on the germanium content, it has been found that, whereas Cu2ZnSnS4 (x=0) crystalizes in the tetragonal structure, the Cu2ZnSn1- xGexS4 system constitutes a solid solution and adopts the orthorhombic structure for x > 0.25. Below this value, a two-phase region exists. Quaternary chalcogenides with formula I2–II–IV–VI4 have recently attracted much attention due to their anisotropic structures, nonlinear optical properties and energy clean conversions. Numerous applications fields, such as energy, environment and opto-electronics, make them potential candidates as thin-film solar cells absorber layers. Members of one group of materials, copper-based quaternary semiconductors, namely Cu2ZnSn(S,Se)4 (CZTSSe) has achieved an efficiency of 12.6 %. It remains far below the Cu(In,Ga)Se2 (CIGSe) solar cells efficiency (21.7%). Such enhancement of the efficiency for the later is mainly related to the absorber band-gap which varies with the Ga/In substitutions. In the case of CZTSSe material, partially substituting Ge by Sn should lead to an analog result. CZTS compound crystallizes in the tetragonal structure while CZGeS may crystallizes in the tetragonal stannite-type structure (space group ̅ ) or in the orthorhombic structure (space group Pmn21). In this study, we investigate the effect of the Ge content on the structural, vibrational and morphological properties of Cu2ZnSn1-xGexS4 (CZTGS). The CZTGS compounds were synthesized by solid state reaction with various Ge/Sn substitutions. Based on the X-ray analysis, we found that the Cu2ZnSn1-xGexS4 orthorhombic structure type is present for x > 0.25. In this case, all of the lattice parameters (a, b, c and volume) obey the Vegard’s law, and let us confirm that the Cu2ZnSn1-xGexS4 system constitutes a solid solution with space group Pmn21. However, for x < 0.25, a two-phase region was observed. Nevertheless, additional studies are in progress to exactly determine the miscibility gap region.
Authors : K.A. Gonchar1,2, A.A. Zubairova1, V.A. Georgobiani1, L.A. Osminkina1,3, V. Sivakov4, V.Yu. Timoshenko1,3
Affiliations : 1Department of Physics, M.V.Lomonosov Moscow State University, Leninskie Gory 119991 Moscow, Russia;2Theoretical Physics and Applied Mathematics Department, Ural Federal University, 19 Mira street 620002 Ekaterinburg, Russia;3Bio-nanophotonics Laboratory, National Research Nuclear University “MEPhI” (Moscow Engineering Physics Institute), 31 Kashirskoe sh., 115409 Moscow, Russia;4Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9 D-07745 Jena, Germany
Resume : Recent years scientific community attention has been transferred from porous silicon to arrays of Si nanowires (SiNWs) formed by metal-assisted chemical etching (MACE) due to high perfection of its crystal lattice and surface properties. Usually in MACE hydrofluoric acid (HF) was used. But in this work we tried to use green chemistry and HF was changed on NH4F. This procedure made MACE safer and environmentally friendly. Optical properties (total reflectance, interband photoluminescence (PL) and Raman scattering) of SiNWs formed by MACE using green chemistry were investigated. The total reflectance of c-Si is near 30%-40% for the visible spectral range, opposite to SiNWs, which exhibit a strong decrease of the total reflectance. The Raman scattering intensity increases strongly for SiNWs in comparison with the corresponding value of c-Si substrate. Also PL in visible spectral range from SiNW arrays was observed. All these results suggest similar optical properties of SiNWs obtained using green chemistry to the SiNWs obtained by the standard MACE method. It gives an opportunity to obtain high quality SiNWs for various applications in photonics and photovoltaics using green chemistry.
Authors : P. R. Wiecha, A. Arbouet, C. Girard, V. Paillard
Affiliations : CNRS-CEMES and University of Toulouse
Resume : High refractive-index dielectric nanostructures provide original optical properties thanks to the occurrence of size- and shape-dependent optical resonances. They have thus attracted increasing interest as low-loss alternatives to plasmonic particles. Likewise, nonlinear optical effects play an important role in photonics, providing various functionalities such as harmonic generation or all-optical signal processing. Semiconductor nanostructures are promising for enhancing intrisically weak nonlinear effects due to strong electric fields at resonant optical modes. We focus on Second Harmonic Generation (SHG) from silicon nanowires (SiNWs), which is forbidden in the bulk of the centrosymmetric Si lattice. Hence, SHG can occur only if this symmetry is locally broken, for instance at interfaces or due to strong field gradients. Such limitations can be overcome in SiNWs, thanks to the high surface-to-volume ratio together with field enhancement by resonant modes. We thus show that SHG can be enhanced by two orders of magnitude compared to bulk Si. We also show that surface and bulk-like contributions to SHG can be distinguished by appropriate polarization selection rules. Finally, we observe a size-dependent transition in the contributions to SHG. In small NWs SHG from field gradients in the bulk dominates, while in larger NWs surface contributions are mainly responsible for SHG. In summary, Si nanowires provide a useful tool for nonlinear silicon photonics.
SERS III : Simion Astilean
Authors : B. Fazio, C. D'Andrea, A. Foti, E. Messina, A. Irrera, M. G. Donato, V. Villari, N. Micali, O. M. Marago' and P. G. Gucciardi
Affiliations : CNR - Istituto Processi Chimico-Fisici, Viale F. Stagno D'Alcontres 37, I-98158 Messina, Italy
Resume : We report on a novel scheme  that exploits the radiation pressure to locally push gold nanorods and induce their aggregation in buffered solutions of biomolecules, achieving biomolecular SERS detection at almost neutral pH. The sensor is applied to detect non-resonant amino acids and proteins, namely Phenylalanine, Bovine Serum Albumin (BSA), Lysozyme, Catalase, Hemoglobin, reaching detection limits in the µg/mL range. Quantitative detection of protein is demonstrated for BSA, down to 50 mM concentrations. Our methodology is chemical free , easy to implement, fast to operate, and has potential for integration in microfluidic circuits for biomarkers detection applications.  B. Fazio et al., Sci. Rep. 6, 26952 (2016).
Authors : ZHANG Zhengjun, MA lingwei, HOU mingling, Huang yu
Affiliations : Tsinghua University
Resume : We report that using Ag nanorods as effective surface-enhanced Raman scattering substrates, one can recognize chemicals at trace levels based on their Raman spectra fingerprints, where the degradation of the SERS sensitivity is a major concern. We found that by covering Ag nanorods with ultra thin Al2O3 layers as SERS substartes, its sensitivity, thermal stability, chemical stability, reusability, etc, can be greatly improved. This make Ag nanorods work as SERS substrates even in very harsh environments and corrosive chemicals. Based on the principle components analysis methods, we proposed a triangle rule and a balance rule to calculate the composition of chemical mixtures at trace levels, with which one can easily recognize chemicals at trace levels, and calculate the relative compositions of the chemical mixtures. Based on the partial least square regression method, one can calculate quantitatively the amount and composition of chemicals at trace levels. This make a step forward to the real application of SERS in the chemical detections/sensing devices.
Authors : Valery Kopachevsky1, Sergej Shashkov1, Kseniya Girel2, Hanna Bandarenka2, Vitaly Bondarenko2, Andrei Panarin3, Sergei Terekhov3
Affiliations : 1SOL Instruments Ltd., 58-10, Nezalezhnasti av., Minsk 220005 Belarus 2Belarusian State University of Informatics and Radioelectronics, 6 Brovka st., Minsk 220013 Belarus 3B.I. Stepanov Institute of Physics of National Academy of Sciences of Belarus, 68 Nezalezhnasti av., Minsk 220072 Belarus
Resume : This work reports on formation of plasmonic metal nanostructures by porous silicon (PS) templating, their properties and application as substrates for surface enhanced Raman scattering (SERS) spectroscopy. We present technological features, which allow to manage surface plasmon band position from blue to near-IR range and to meet principal requirements to SERS substrates such as ultralow limit of detection, spot-to-spot and sample-to-sample reproducibility, long shelf life. Special attention is focused on composition and morphology of the metal nanostructures (dendrites, nanoparticles, nanorods, nanovoids), which can be grown by variation of metal (Ag, Ni, Cu) and PS types (micro, meso, macro). It is shown that PS acts not only as a template for definition of dimensions, shape and mutual arrangement of the metal nanostructures, but also highly improves their stability to oxidation. SERS measurements were performed with 3D scanning laser confocal Raman microscope Confotec NR500. It provided accurate definition of potential “hot spots” location in the substrates and study of kinetics of the Raman signal degradation upon laser excitation. The PS-based SERS substrates demonstrated the limit of detection ranging from nano- to femtomolar concentration depending on the type of analyte. In conclusion, advantages of SERS substrates based on PS such as simplicity, cost-effectiveness and compatibility with silicon technology in comparison to other nanoengineered ones are considered.
Authors : Jiahong Li, Xuan Du, Wenjun Zhang*
Affiliations : Huazhong University of Science and Technology;City University of Hong Kong
Resume : In this paper, we successfully fabricated periodic silver Nano-arrays (SNAs) fabricated on porous anodic titania template by a simple physical exfoliation method as the surface enhanced Raman and fluorescence substrate. SERS was investigated for low concentration R6G which was deposited on the SNAs. SEF was proved by PL spectrum of R6G and the signal of cytoskeletal structure which was labeled by fluorochrome. The experiment showed that the Raman signal and fluorescence strength achieved greatly enhanced and the fluorescence signal of cytoskeleton increased obviously, stronger photo-stability compared with the smooth silver film. Moreover, the template could be repeatedly used to ensure the reproducibility and stability. This method provides a sensitivity and inexpensive technique to create period silver Nano-arrays for various applications such as Medical diagnosis and biosensor.
Poster Session 2 : Katarzyna Siewierska
Authors : (1) V.V. Strelchuk, S.A. Kravchenko, (2) V.I. Korzhov, (3) L.A. Bulavin, B.O. Golichenko
Affiliations : (1) V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine; (2) SO "National institute of phthisiology and pulmonology named after F.G. Yanovsky NAMS of Ukraine"; (3) Taras Shevchenko National University of Kyiv, Ukraine
Resume : Due to the growing need in detection of molecules of organic and non-organic nature at low concentrations, the active design of universal substrates for Surface-Enhanced Raman Scattering (SERS) is carried out. Besides this, researchers move toward optimizing the parameters of the substrates – particles size, their aggregation and arrangement on the surface. One of the most prevalent direction is a development of affordable substrates with colloidal gold and silver nanoparticles for express diagnostics of certain molecular species, that have to consist with the optical parameters of analyte and experimental conditions. SERS-substrates prepared by means of the Tollens' reaction (the mirror reaction) were used for the detection of low concentrations of biological species (Adenine, amino acids, Hemoglobin). Thin island-like films consisting of silver nanoparticles were formed on glass substrates with the Tollens' reaction. The efficiency of SERS-enhancement is known to be very sensitive to the morphology of the silver film. Also, the typical size of the distinct nanoparticles and it`s aggregates made an impact on plasmonic properties of the SERS-substrate. The surface morphology was varied by reaction conditions (reagent concentration and reductant character) and was controlled by Atomic Force Microscopy (AFM) after preparation. Different ways of interface formation between substrate surface and silver film in order to improve SERS substrate reproducibility were studied.
Authors : Raymond Gillibert (1 2), Mitradeep Sarkar (3), Jean François Bryche(3 4), Ryohei Yasukuni (1), Julien Moreau(3), Mondher Besbes(3), Grégory Barbillon (4), Bernard Bartenlian (4), Michael Canva (3 5), Marc Lamy de la Chapelle (1)
Affiliations : (1) Université Paris 13, Sorbonne Paris Cité, Laboratoire CSPBAT, CNRS UMR 7244, Bobigny, France; (2) HORIBA Jobin Yvon S.A.S. Villeneuve d'Ascq, 231 rue de Lille 59650 Lille, France; (3) Institut d'Optique Graduate School, Laboratoire Charles Fabry CNRS UMR 8501, Palaiseau, France; (4) Université Paris-Sud, Institut d'Électronique Fondamentale CNRS UMR 8622, Orsay, France; (5) Université de Sherbrooke, Laboratoire Nanotechnologies Nanosystèmes, LN2, UMI CNRS 3463, 3IT. Qc Canada;
Resume : Directional plasmon excitation and SERS emission were demonstrated for 1D and 2D gold nanostructure arrays deposited on flat gold layer. Extinction spectrum of both arrays exhibits intense resonance bands that are red shifted when the incident angle is increased. Systematic extinction analysis of different grating periods revealed that this band can be assigned to a propagated surface plasmon of the flat gold surface that fulfills the Bragg condition of the arrays (Bragg mode). Directional SERS measurements demonstrated that the SERS intensity can be improved by one order of magnitude, when the Bragg mode positions matched with either the excitation or the Raman wavelengths. Hybridized numerical calculations of Finite Element Method and Fourier Modal Method also proved the presence of Bragg mode plasmon and illustrated that the enhanced electric field of the Bragg mode is particularly localized on the nanostructures regardless of their size.
Authors : Raymond Gillibert (1 2), Mitradeep Sarkar (3), Michael Canva (3 4), Marc Lamy de la Chapelle (1)
Affiliations : (1) Chimie, Structures, Propriétés de Biomatériaux et d'Agents Thérapeutique (CSPBAT) UMR 7244, France; (2) HORIBA Jobin Yvon S.A.S. Villeneuve d'Ascq, 231 rue de Lille 59650, France; (3) Institut d'Optique Graduate School CNRS, Laboratoire Charles Fabry, Palaiseau, 91127, France; (4) Université de Sherbrooke, Laboratoire Nanotechnologies Nanosystèmes, LN2, UMI CNRS 3463, 3IT. Qc Canada;
Resume : Plasmonic properties of arrays of gold nanodisks were investigated in order to study the localization of the near-field enhancement at the surface of the nanodisks. To measure the near field, Surface enhanced Raman spectroscopy (SERS) was performed on different kind of substrates with and without an over layer of silica that disabled the possibility for our SERS probe to adsorb on the top of our structures. Thanks to this we were able to determine, depending on the substrate, which fraction of the SERS enhancement was coming from the top of our structures. We demonstrate that the near-field enhancement is mainly localized at the top of the nano disks in the case of ITO substrate whereas it comes from the nanodisk side for gold substrate.
Authors : Andreia Araújo1*, Carlos Caro2, Manuel J Mendes1, Daniela Nunes1, Elvira Fortunato1, Ricardo Franco2, Hugo Águas1* and Rodrigo Martins1
Affiliations : 1 i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal 2 REQUIMTE, UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
Resume : This work reports on highly efficient surface enhanced Raman spectroscopy (SERS) constructed on low-cost, fully recyclable and highly reproducible cardboard plates, which are commonly used as disposable packaging material. The active optical component is based on plasmonic silver nanoparticle structures separated from the metal surface of the cardboard by a nanoscale dielectric gap. The SERS response of the silver (Ag) nanoparticles of various shapes and sizes were systematically investigated, and a Raman enhancement factor higher than 106 for rhodamine 6G detection was achieved . The spectral matching of the plasmonic resonance for maximum Raman enhancement with the optimal local electric field enhancement produced by 60 nm-sized Ag NPs predicted by the electromagnetic simulations reinforces the outstanding results achieved. Furthermore, the nanoplasmonic SERS substrate exhibited high reproducibility and stability. The SERS signals showed that the intensity variation was less than 5%, and the SERS performance could be maintained for up to at least 6 months.  Andreia Araújo, Carlos Caro, Manuel J Mendes, Daniela Nunes, Elvira Fortunato, Ricardo Franco, Hugo Águas and Rodrigo Martins, Highly efficient nanoplasmonic SERS on cardboard packaging substrates, Nanotechnology 25 (2014) 415202.
Authors : Chen Xu,a,b,‡ Yibao Zhou,a,b,‡ Shuangbao Lyu,a Huijun Yao,a Dan Mo,a Jie Liu,*a Jinglai Duan*a
Affiliations : a Materials Research Center, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China. Email: email@example.com (JL); firstname.lastname@example.org (JLD) b School of Physical Science and Technology, Lanzhou University, China. ‡ CX and YZ are visiting undergraduate students from the School of Physical Science and Technology, Lanzhou University
Resume : Surface enhanced Raman spectroscopy (SERS) is a label-free and non-destructive vibrational spectroscopy technique that allows for ultrasensitive and fast structural detection of trace-level molecules through the enhanced electromagnetic (EM) fields amplified by the excitation of localized surface plasmon Resonances (LSPR). Compared to conventional rigid SERS substrates, e.g. glass and silicon, flexible substrates provide flexibilities of configurable assembly which is critical to the applications such as on-line trace level detection. In addition, large-scale production is another concern for reducing cost. In this work, we demonstrate a new type of double-sided, large-scale, and flexible metasurfaces for ultrasensitive, highly uniform, polarization-independent SERS detection. The SERS substrates are fabricated by simply sputtering densely packed gold nanoparticles on porous polycarbonate membranes which composed of conical pores created by asymmetric etching of ion tracks. Morphological characterizations reveal that the conical pores are uniformly distributed on both sides of membranes and uniform in shape and size. The porous polycarbonate membranes are covered with granular gold films which typically have sub-5 nm gaps among adjacent particles. Such metasurfaces show ultrasensitive SERS detection limit down to 10 pM which is comparable to the reported highest value (1 pM) for flexible substrates. The high uniformity is reflected by a low relative standard deviation (RSD) ~10% over the entire wavenumber range (300-1800 cm-1). Numerical simulations disclose that the enhanced EM fields of granular gold films are further amplified by conical pores. Such hierarchical metasurfaces represent a step forward to low-cost, high performance, and reliable flexible platforms for ultrasensitive SERS detection.
Authors : M. Baillieul 1,2, E. Baudet 3, A.J. Gutierrez-Arrovo 4, F. Verger 1,2, F. Colas 1, E. Rinnert 1, P. Němec 3, J. Charrier 4, L. Bodiou 4, K. Boukerma 1, C. Boussard 2, B. Bureau 2, K. Michel 5, T. Toury 6, M. Lamy de la Chapelle 7, V. Nazabal 2
Affiliations : 1 IFREMER, Laboratoire Détection, Capteurs et Mesures, 29280 Plouzané, France 2 ISCR, UMR-CNRS 6226, Equipe Verres et Céramiques,Université de Rennes 1, 35042 Rennes, France 3 Department of Graphic Arts and Photophysics, Faculty of Chemical Technology, University of Pardubice, Studentska 573, 53210 Pardubice, Czech Republic 4 FOTON, UMR CNRS 6082, Enssat, 6 rue de Kerampont, BP 80518, 22305 Lannion, France 5 BRGM, Direction Eau, Environnement et Ecotechnologies, Unité Bio-Géochimie environnementale et qualité de l’Eau, 45060, Orléans, France 6 ICD-LNIO, UMR STMR CNRS 6279, Université de technologie de Troyes, 10000 Troyes, France 75 Université Paris 13, Sorbonne Paris Cité, Laboratoire CSPBAT, CNRS, UMR 7244, 93017 Bobigny, France
Resume : The development of Mid-IR sensors for monitoring the concentrations of organic pollutants in the aquatic environment is currently a challenge of great importance. Mid-infrared range (4000-400 cm-1) contains the absorption bands related to the vibrations of organic molecules. The mid-infrared sensor based on evanescent wave spectroscopy is a promising analytical tool for simultaneous detection and quantification of a variety of pollutants such as hydrocarbon compounds. Chalcogenide glasses are particularly well adapted for sensing applications due to their high refractive index (between 2 and 3). The aims of this study were to synthetize chalcogenide thin films for developing mid-IR optical integrated platforms and perform their functionalization by polymers in order to increase the sensor sensitivity. Among (GeSe2)100-x(Sb2Se3)x glass compositions, two selenide glass targets were chosen for their mid-IR transparency, stability against crystallization and refractive index contrast suitable for mid-IR optical wave-guiding. Infrared selenide waveguides were fabricated by radiofrequency magnetron sputtering and functionalized by a polyisobutylene polymer. By means of attenuated total reflection spectroscopy, measurements were performed in water to detect aromatic hydrocarbons (benzene, toluene and three xylene isomers) in the concentrations range of 10 ppb to 40 ppm. Consequently to minimize the water absorbance, the ZnSe prism surface was successfully modified by a thin hydrophobic coating. Moreover, hydrocarbons detection was also carried out using selenide thin film deposited on ZnSe prism surface to mimic and assess the efficiency of a chalcogenide optical platform. Detection measurements have been fulfilled using sea and ground water. To increase the sensor sensitivity, the use of metallic nanoparticles is one of the promising solutions based on Surface Enhanced Infrared Absorption. Hetero-structures combining gold nanoparticles/chalcogenide glass and waveguides were fabricated and characterized. To assess Surface Enhanced Infrared Absorption, we used a self-assembled monolayer of 4-nitrothiophenol randomly oriented with strongest bands located at 1336 and 1512 cm-1 attributed to NO2 symmetric and antisymmetric stretching modes, respectively. Using various morphologies, thicknesses or inter-particles coupling, an enhancement factor varying from 25 to 106 was calculated to detect 4-nitrophenol. References : J. Charrier et al "Evanescent wave optical micro-sensor based on chalcogenide glass," Sensors and Actuators B-Chemical 173, 468-476 (2012) F. Verger et al, "RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy," Optical Materials Express 3, 2112-2131 (2013). F. Verger et al "Surface enhanced infrared absorption by nanoantenna on chalcogenide glass substrates," Appl. Phys. Lett. 106 (2015) Aknowledgement : Authors are thankful to ANR for LOUISE project funds.
Authors : N. M. Martynova, A. V. Grigorieva, E. A. Goodilin .
Affiliations : Department of Materials Science, Lomonosov Moscow State University, Moscow 119991, Russia
Resume : Surface-enhanced Raman spectroscopy (SERS) is universal method for analysis of small quantities of organic analytes with high sensitivity . It is a multiple times enhancement of the Raman signal from the analyte molecules located on a substrate, comprising individual nanoparticles or nanostructured films of noble metals. As a result of laser irradiation on the metal surface plasmons generated by increasing the electric field around the metal, which increases the Raman signal intensity up to 1011 times. It is remarkable that different analytes absorb (and fluoresce) at different wavelengths, and so lasers of different energies should be used. Therefore, an urgent task is to form a substrate for SERS spectroscopy which has multiband plasmon resonance in a wide energy range. In this project, gold inverse opals with wholly or partly hexagonally ordered pores are proposed as SERS-active substrates. The aim of this work is the formation of gold inverse opals using different electrolytes, study of the correlation of optical properties of the films with their morphology peculiarities, as well as the use of obtained samples as SERS-active substrates. Synthesis of inverse opals consists of several stages: obtaining polystyrene microspheres, formation of colloidal crystals, electrocrystallization of gold in pores of matrix, and its subsequent removal . The quality of the samples at each step influences the final structure of the porous gold film. Au inverse opals were prepared by electrochemical deposition of gold from chloride, citrate or sulfite electrolytes into ordered matrices consisting of microspheres with diameter D = 400 and 530 nm, as well as into disordered matrices consisting of microspheres with D = 200, 300, 500 and 600 nm. (with standard deviation less than 5%). It should be added that the electrolyte composition may affect on particles size, and hence, on plasmon resonance bands. In current project optimal parameters for ordered colloidal crystals formation are found (temperature, concentration of suspension, electric field intensity). Based on them, Au inverse opals are obtained with various normalized thicknesses in the range 0.05 ÷ 1.1 of microsphere diameter in the matrix. For electrodeposition of Au, optimal conditions are found: chloride electrolyte, deposition in potentiostatic mode at Ed = 0.8 V versus Ag / AgCl reference electrode. Figure 1. SEM data of gold inverse opals. Measuring of reflection spectra was performed by varying incidence angles and azimuthal angles. On reflection spectra of the samples a number of various plasmon resonance features are observed. Resonances are associated with the presence of local plasmons of individual particles, Mie and Bragg plasmons in a mixed state . The condition of Mie and Bragg plasmon excitation is determined only by surface morphology depending on period and thickness of porous gold films. Intense local plasmon resonance is typical for all gold films of different crystallinity and its profile depends on grain size varied in the range of 20-50 nm and through this on reflectivity characteristic in 400-1000 nm range. Using XPS method surface composition of the gold films was analyzed to reveal presence of adatoms which could result from different electrolyte compositions. The Raman data, obtained on substrates, show an increased intensity of the Raman signal from fluorescent dyes rhodamine 6G and methylene blue at concentrations up to 10-10 M (volume of aliquot ~ 1 mkl) by their excitation with green (λ = 514 nm) and red (λ = 633 nm) lasers, respectively. The spectra obtained from different parts of the substrates are identical, suggesting about the reproducibility of samples and surface uniformity of substrates. The enhancement factor in the case of methylene blue is G = 106 for most of the concentrations of aliquote. After washing substrates with distilled water, microstructure of the substrates reveals no changes, and SERS effect is observed, that demonstrates the SERS-active substrate to be renewable. Authors wish to acknowledge their colleagues, namely, Dr. K.S. Napolskii and Dr. N.A. Sapoletova for their assistance with experiments and fruitful discussion of experimental results. Authors gratefully acknowledge the support of the Russian Foundation of Basic Research under grant No 15-33-70050-mol_a_mos. References  Semenova A A, Goodilin E A, Brazhe N A, Ivanov V K, Baranchikov A E, Lebedev V A, Goldt A E, Sosnovtseva O V, Savilov S V, Egorov A V, Brazhe A R, Parshina E Y, Luneva O G, Maksimov G V, Tretyakov Y D. 2012 J. Mater. Chem. 22 24530  Sapoletova N A, Martynova N A. Napolskii K S, Eliseev A A, Lukashin A V, Kolesnik I V, Petukhov D I, Kushnir S E, Vassilieva A V, Grigoriev S V, Grigoryeva N A, Mistonov A A, Byelov D V, Tretyakov Y D. 2011 Physics of the solid state 53 (6) 1126-1130  Kelf T A, Sugawara Y, Cole R M, Baumberg J J, Abdelsalam M E, Cintra S, Mahajan S, Russell A E, Bartlett P N. 2006 Phys. Rev. B 74 (24) 245415
Authors : Andreia Araújo1, Ana Pimentel1, Maria João Oliveira1, Manuel J. Mendes1, Ricardo Franco2, Elvira Fortunato1, Hugo Águas1* and Rodrigo Martins1*
Affiliations : 1i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, UniversidadeNOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal 2REQUIMTE, UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
Resume : Paper substrates, covered with ZnO nanorods (NRs) coated with Ag nanoparticles (NPs), allowed the production of inexpensive, high-performing and highly reproducible SERS platforms. The ZnO NRs were synthesized by a simple, fast and low-temperature hydrothermal method assisted by microwave radiation and made SERS-active by decorating them with a dense array of silver nanoparticles deposited via a single-step thermal evaporation technique.1 Using Rhodamine 6G as the probe molecules, with a concentration down to 10-9 M, the SERS substrates present up to 107 Raman enhancement with good reproducibility. The increase of the sensing area, provided by the ZnO NRs scaffold, dramatically increases the density of hot spots responsible for SERS and is, therefore, key to the pronounced Raman enhancement. The results demonstrate that plasmonic paper, covered with Ag NPs@ZnO NRs, is an efficient SERS platform with the advantages of being recyclable, flexible, lightweight, portable, biocompatible and extremely low-cost. Araújo, A.; Caro, C.; Mendes, M. J.; Nunes, D.; Fortunato, E.; Franco, R.; Águas, H.; Martins, R. Highly Efficient Nanoplasmonic SERS on Cardboard Packaging Substrates. Nanotechnology 2014, 25 (41), 415202.
Authors : Y. Rajesh, L.D. VarmaSangani, Ummar Pasha Shaik, AnshuGaur, Md Ahamad Mohiddon, M.GhanashyamKrishna
Affiliations : School of Physics, University of Hyderabad, Hyderabad 500046, Telangana, India; Centre for Advanced Studies in Electronics Science and Technology, University of Hyderabad; Advanced Center of Research in High Energy Materials, University of Hyderabad, Hyderabad 500046; Department of Science and Humanities, National Institute of Technology Andhra Pradesh, Tadepalligudem, 534101, Andhra Pradesh, India.
Resume : The role of dielectric surrounding on Au nanostructure for surface plasmon resonance (SPR) behavior is investigated by scanning near field optical microscopy (SNOM). The near field optical field strengths are correlated with the surface enhanced Raman scattering (SERS) enhancement factors. Discontinuous nanostructured Au thin films are deposited by RF magnatron sputtering at very slow rate on three different dielectric materials, ZnO, TiO2 and SiO2. The discontinuity of Au nanostructure was confirmed through scanning electron microscopy (SEM) and atomic force microscopy (AFM). Transparent, continuous and smooth surface dielectric films of ZnO and TiO2 are grown onto borosilicate glass (BSG) substrate by two different techniques. ZnO films are deposited by thermal evaporation of pure ZnO powder. TiO2 films are obtained by the spin coating of the sol-gel derived solvents. Both films are heat treated to appropriate temperatures, to obtain an optimized situation of relatively good crystallization and low surface roughness. The crystal phase formation and surface roughness are investigated by x-ray diffraction and AFM technique simultaneously. A bare BSG substrate of 150 μm thick is used as the third dielectric surrounding in the present study. The role of dielectric material on the SPR behavior of Au/dielectric nanostructure is demonstrated by recording the SPR absorption in the range of 200-1000nm. These three Au/dielectric nanostructures are investigated using SNOM by illuminating it in near field and collecting in transmission far field configuration. The observed optical near field images of the three different nanostructures are discussed by taking their dielectric constant into the account. These three Au/dielectric nanostructures are investigated for SERS application using Rhodamine 6G dye molecule. The calculated SERS enhancement factors are compared with the optical field strengths derived from the near field optical imaging.
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SERS IV : Pietro G. Gucciardi
Authors : John Gough, Katarzyna Siewerska, Sam Mehigan, Damien Hanlon, Claudia Backes, Zahra Gholamvand, Beata Szydloska, Werner Blau, Eithne McCabe, A. Louise Bradley
Affiliations : School of Physics and CRANN, Trinity College Dublin, Ireland.
Resume : The interplay between metal enhanced fluorescence/quenching and surface enhanced Raman scattering (SERS) is a factor of paramount importance in determining the applicability of a substrate for SERS of fluorescent molecules. In this contribution we present complimentary studies of fluorescence and SERS detection on graphene oxide (GO) and Ag nanoparticle-graphene oxide (AgGO) composite substrates for three organic dyes; Rhodamine 6G (R6G), Rhodamine B (RhB), and Sulforhodamine 101 (SR101). The three dyes have different quantum yields and overlap different regions of the collective Ag nanoparticle extinction spectrum. While all three dyes exhibit fluorescence quenching on the AgGO composite, R6G and SR101 demonstrate larger SERS peak signal-to-noise ratios (SNRs) and enhancement factors (EF) on the AgGO substrate than observed for RhB. The influence of fluorescence quenching on the SERS detection was explored through characterisation of the dyes’ spectra and time-resolved emission on the GO and AgGO substrates. Strong correlation was observed between the SERS SNR and time-resolved photoluminescence data, and the factors contributing to the overall enhanced SERS detection for each dye could be elucidated. It is seen that emission quenching by the GO component is a more significant factor in the SERS SNR and EF for R6G than for SR101. The time-resolved PL data also shows that SR101 couples most strongly to the Ag NPs, and is thus able to benefit most from direct enhancement of the Raman scattering signal.
Authors : F. Jimenez-Villacorta, E. Climent-Pascual, X.A. Pujol, L. Alvarez-Fraga, R. Ramirez-Jimenez, C. Prieto and A. de Andres
Affiliations : Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas. Cantoblanco 28049 Madrid, Spain
Resume : Two different types of nanostructures, Ag nanoislands of ~40 nm average (in-plane) diameter and Ag ultrasmall nanoparticles of ~4 nm diameter, were studied as active plasmonic components to be implemented in SERS platforms. Nanoislands provide an optimized value of plasmon resonance intensity, whereas ultrasmall nanoparticles are envisioned to provide a large hot spot areal density. It has been observed that high surface density silver ultrasmall nanoparticles (>1 monolayer) and percolated silver nanoislands reveal an unambiguous increase of the plasmon resonance intensity with time in the early stages of the process. This can be explained in terms of formation of Ag/AgOx core/shell entities with concomitant suppression of particle connectivity, introducing new hints in the development of silver-based materials for SERS detection. Moreover, unlike what was anticipated, the plasmon resonance in both systems is quite stable and visible throughout a long-term period of time. On the other hand, the graphene layer in graphene/Ag NPs, besides its role as molecule immobilizer and fluorescence quencher, yields delocalization of the plasmon resonance along the visible range. This effect gives additional hints of the SERS performance to a broader excitation wavelength range. Implementation of these two types of nanostructures in SERS platforms (e.g., graphene/Ag NPs/Al2O3/Al/Si heterostructures, with combined surface and interference Raman amplification contributions) are analyzed.
Authors : Igor Dzięcielewski, Jan Weyher, Jan Krajczewski, Andrzej Kudelski
Affiliations : Institute of High Pressure Physics of the Polish Academy of Science, Institute of High Pressure Physics of the Polish Academy of Science, The Faculty of Chemistry, University of Warsaw, The Faculty of Chemistry, University of Warsaw
Resume : A good quality SERS substrate should provide a high enhancement factor (EF) combined with surface uniformity, stability and reproducibility of obtained spectra. These features provide highly reliable results also enabling time-lapse measurements which tend to be crucial in biological systems. We introduced novel SERS platforms based on etched gallium nitride coated with a nanometric layer of either gold or gold alloy. This system provided the mechanical stability and high surface roughness of GaN combined with high enhancement factor and chemical stability of gold. This feature enabled time-lapse measurements of various biological systems such as Hepatitis B virus antigen and DNA. In order to increase the EF and the overall quality of the system we introduced new types of coatings (silver-gold and copper-gold alloys) and ways to modify them by various means. We are able to further increase the surface area and chemical composition of existing layer by wet chemical etching. Moreover, by heat treatment we are able to change the shape, size and crystallographic form of gold further increasing the EF of platform. We have also developed methods to tune hydrophobic properties of the sample surface. Above mentioned gold layer and surface modification techniques enable fitting for individual applications making it better tool for new applications. In this presentation we would like to share with You results and highlight new application opportunities and challenges.
Authors : Ivano Alessandri
Affiliations : INSTM and University of Brescia
Resume : Core/shell nanostructures are intensively investigated for broadband light trapping and management, because they can play as optical cavities by taking advantage of light-trapping and morphology dependent resonances. The same properties can be exploited in imaging and vibrational spectroscopy (Raman, IR), in order to enhance their analytical sensitivity. [1-5] Moreover, the synergistic combination of plasmonic nanoantennas and dielectric core/shell colloids are leading to the fabrication of near-field optical light concentrators. These structures are very efficient in stimulating photon-driven processes at metal-semiconductor interfaces and show an impressive decrease in degradation time (minutes instead of hours) of organic pollutants.  This presentation will review some applications of core/shell light nanoconcentrators as non-plasmonic Raman enhancers, which have been used to investigate biochemical reactions in aqueous environment [3,5] or to detect environmental CO2,  and their coupling to plasmonic nanoantennas for promoting and in-situ monitoring light-assisted chemical reactions.  References 1) I. Alessandri, J. Am. Chem. Soc. (2013) 135(15), 5541-5544. 2) I. Alessandri et al., RSC Adv. (2014) 4, 38152-38158 3) I. Alessandri et. al., Small (2014) 10, 1294-1298. 4) N. Bontempi et al., Nanoscale (2016) 8, 3226-3231. 5) I. Alessandri et al., ACS-Appl. Mater. Interf., accepted, doi: doi:10.1021/acsami.5b08190. 6) M. Salmistraro et al., Small (2013) 9, 3301-3307.
PV VI : Vladimir Simirnov
Authors : Seweryn Morawiec (2), Jakub Holovský (3), Manuel J. Mendes (1,4), Martin Müller (3), Kristina Ganzerová (3), Aliaksei Vetushka (3), Martin Ledinský (3), Francesco Priolo (1,2,5), Antonin Fejfar (3), and Isodiana Crupi (1).
Affiliations : 1 MATIS IMM-CNR, via S. Sofia 64, I-95123 Catania, Italy. 2 Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia 64, I-95123 Catania, Italy. 3 Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Prague, Czech Republic. 4 CENIMAT/I3N, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa and CEMOP/UNINOVA, 2829-516 Caparica, Portugal. 5 Scuola Superiore di Catania, Università di Catania, via Valdisavoia 9, 95123 Catania, Italy.
Resume : We apply a combination of photocurrent and photothermal spectroscopic techniques to experimentally quantify the trade-off between useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (?c-Si:H) films incorporating self-assembled silver nanoparticle arrays, located at the rear side, for improved light trapping via resonant plasmonic scattering. The photothermal technique is used to measure the total absorptance while the photocurrent spectroscopy accounts only for the photons absorbed in the ?c-Si:H layer (useful absorptance); therefore, the method allows for independent quantification of the useful and parasitic absorptance of the plasmonic (or any other) light trapping structure . We demonstrate that for 0.9 ?m thick ?c-Si:H film the optical losses resulting from the plasmonic light trapping are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. For the films deposited on nanoparticle arrays coupled with a flat silver mirror (plasmonic back reflector), we achieved a significant broadband enhancement of the useful absorption with an average useful absorption of 43% and an average parasitic absorption of 19% over 400?1100 nm wavelength range, achieving 91% of the theoretical Lambertian limit of absorption.  S. Morawiec et al. Experimental Quantification of Useful and Parasitic Absorption of Light in Plasmon-Enhanced Thin Silicon Films for Solar Cells Application. Scientific Reports 6 (2016)
Authors : R. Pietruszka1, B. S. Witkowski1, K. Kopalko1, S. Gieraltowska1, E. Zielony2, K. Gwozdz2, P. Bieganski2, E. Placzek-Popko2, M. Godlewski1,3
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 2Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wroclaw, Poland 3Department of Mathematics and Natural Sciences College of Science, Cardinal Stefan Wyszynski University, Warsaw, Poland
Resume : ZnO, a wide band gap semiconductor with 3.3 eV band gap at room temperature, is intensively studied for photovoltaic (PV) applications - mostly as a transparent conductive oxide (TCO) and/or as a n type partner for p-type materials (e.g. Si, CdTe, CIGS…). In this work, we study PV structures based on n type ZnO layers and ZnO nanorods (ZnONR) on p-type Si wafers (2 Ωcm; (100)) with different thicknesses. We used ~50μm and ~200μm Si wafers as a absorbers of solar radiation. Zinc oxide layers and ZnONR were grown by atomic layer deposition method and hydrothermal method, respectively. We focused on the photovoltaic effect in n-ZnO/p-Si solar cells (SC). We evaluated growth conditions, absorbers thicknesses, metal contact etc. in order to obtain the highest PV efficiency. The PV efficiency for such a “new-generation” structures (ZnO:Al/ZnO/ZnONR/Si/Al) equals 14%. This work was partially supported by the National Science Center (decision No.DEC-2012/06/A/ST7/00398), and (Wroclaw group) by the National Laboratory of Quantum Technologies (POIG.02.02.00-00-003/08-00) and Statutory grant S400291.
Authors : Hom N. Luitel, Shintaro Mizuno, Toshihiko Tani, Yasuhiko Takeda
Affiliations : Toyota Central Research and Development Labs., 41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan
Resume : We have developed Ni2+-Er3+ sensitized broadband-sensitive upconverters based on oxide hosts to overcome the shortcoming of conventional Er3+-only doped upconverters used for crystalline-silicon (c-Si) solar cells that utilize only a small fraction of solar spectrum around 1.55 μm. We have designed the combination of sensitizers and host materials to utilize photons that are not absorbed by c-Si itself or Er3+ ions. Six-coordinated Ni2+ ions that absorb near infra-red photons are candidates for the sensitizers. However, Ni3+ and four-coordinated Ni2+ do not function as the sensitizers, because they have longer-wavelength emission bands. La(Ga,Sc)O3 and MZrO3 (M = Ca, Sr, Ba) with ABO3-type perovskite structures are suitable for the host materials, because the ionic radii of the A- and B-site ions are close to those of Er3+ and Ni2+, respectively, and the B sites are six-coordinated at the centers of octahedrons. In addition to (1.4-1.6) μm photons (≈2.01016.cm-2.s-1) upconverted by Er3+ ions alone, we have demonstrated the broadband-sensitive (1.1-1.6 μm: ≈ 8.041016.cm-2.s-1) upconversion to 0.98 μm photons by codoping Ni2+-Er3+ ions, which is about four fold larger. Compared with the current density of the present c-Si solar cells (~40 mA.cm-2), the upconverted photons could increase it by ~7.3 mA.cm-2, which corresponds to ~18% improvement. This architecture for broadband-sensitive upconversion may pave a new direction for the improvements in efficiency of the present c-Si solar cells to surpass the limiting conversion efficiency of single-junction solar cells.
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