Materials for electronics and optoelectronic applications away from silicon.G
Transparent conductive materials: from fundamental understanding to applications
Transparent Conductive Materials (TCM) play a pivotal role in many modern devices such as: solar cells, flexible light-emitting devices, touch screens and flexible transparent thin film heaters. This symposium aims at exploring the most recent ways to better understand the fundamental properties of TCMs and improve their integration in devices.
Transparent, electrically conductive materials (TCM) are important components of displays, touch-screen layers, thin film solar cells, organic light-emitting diodes (OLEDs) and transparent heaters. Conductive oxides such as ITO, AZO or FTO presently have the largest market share. Recent demands for mechanical flexibility and uncertainties in the availability of rare earths spurred the search for alternatives. This symposium aims to bring together research on traditional Transparent Conductive Oxides and emerging TCMs based on graphene, carbon nanotubes, metallic nanowire networks, metallic grids, and composites. The symposium will be concerned with both experimental and modelling approaches, and with the goal of improving their integration in devices.
A compromise between electrical conductivity and transparency imposes several specific requirements including for instance the design of appropriate interfaces and layers with defined microstructures and long-term stability. This symposium will bring together scientists and engineers from universities, research institutes and industries in order to comprehend TCMs properties and work with the target of fabricating stable state-of-the-art transparent electrodes. Deposition of layers containing one or more of the abovementioned conductive nanostructures and their characterization will be the main focus. Theoretical models that provide design rules for conductive layers based on anisotropic or isotropic nanostructures will be covered. Deeper experimental or theoretical insights into the materials will be sought and correlated to mechanisms responsible for key electrical and optical properties. Another focus will be on strategies to overcome limitations of the currently available technologies, and the integration of transparent conductive materials into functional electronic devices. Several keynote speakers will be invited to present their recent scientific contributions. We will also seek industrial contributions to give an insight into the growing commercial relevance of nanostructure-based TCM.
Hot topics to be covered by the symposium:
- TCO electrical and optical properties
- Mechanisms of, and limitations for, electrical conductivity in transparent materials
- Synthesis and processing of novel types of transparent electrode materials
- Optical properties of TCMs: experimental and modelling approaches
- Interface properties of TCMs
- n-type TCOs, p-type TCOs
- Metallic nanowire networks
- Carbon nanotube and graphene based materials
- Composites of metal nanoparticles and polymers
- Composites of carbon-based nanostructures
- Combinations of oxides, metals and carbon-based TCMs
- Diffuse transparent electrodes
- Electrical, thermal, chemical stabilities of transparent electrodes
- Upscaling and advanced large-area processing
- Integration of transparent electrodes into functional devices
- Mechanical flexibility of transparent conductive materials (TCM)
- Modelling and design
Invited speakers (confirmed):
- Delfina Munoz (INES, Bourget-du-Lac, France)
- Qiping Pei (University of California at Los Angeles, USA)
- Joris Proost (University of Louvain, Belgium)
- Thomas Riedl (University of Wuppertal, Germany)
- David Scanlon (University College London, UK)
- Yuzo Shigesato (Aoyama Gakuin University, Japan)
- Benjamin Wiley (Duke University, USA)
- Amelie Catheline (Linde Nanomaterials)
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Transparent Conductive Oxides Part 2 : Junjun Jia
Authors : David O. Scanlon
Affiliations : University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, UK; Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
Resume : The most commercially successful TCO so far is tin doped indium oxide (Indium Tin Oxide ITO), which has become the industrial standard TCO for many optoelectronics applications; the ITO market share was 93% in 2013. Its widespread use stems from the fact that lower resistivities have been achieved in ITO than in any other TCO; resistivities in ITO have reached as low as 7.2 × 10-5Ω cm, while retaining >90% visible transparency. In recent years, the demand for ITO has increased considerably, mainly due to the continuing replacement of cathode ray tube technology with flat screen displays. However, indium is quite a rare metal, having an abundance in the Earths crust of only 160 ppb by weight, compared with abundances for Zn and Sn of 79000 ppb and 2200 ppb respectively, and is often found in unstable geopolitical areas. The overwhelming demand for ITO has led to large fluctuations in the cost of indium over the past decade. There has thus been a drive in recent years to develop reduced-indium and indium-free materials which can replace ITO as the dominant industrial TCO. Recent research has therefore focused both on developing alternative TCOs, such as SnO2, ZnO, and BaSnO3, which are all more abundant and less expensive. In this presentation I will focus on the electronic structure and defect chemistry of Sn-based TCOs, critically analysing them as viable alternatives to ITO.
Authors : Jakub Kaczmarski, Jakub Grochowski, Andrzej Taube, Aleksandra Treichel, Michał A. Borysiewicz, Wojciech Jung, Eliana Kamińska
Affiliations : Institute of Electron Technology, Al. Lotnikow 32/46, 02-668, Warszawa, Poland; Institute of Microelectronics & Optoelectronics, Warsaw University of Technology, ul. Koszykowa 75, 00-662, Warszawa, Poland
Resume : In the following study we report the fabrication of flexible IGZO MESFETs with transparent conductive Ru-Si-O and In-Sn-O, acting as Schottky gate electrode and ohmic source/drain contacts, respectively. The electrode materials were chosen to mitigate interfacial reactions with the IGZO channel. This allows to avoid the standard postdeposition annealing step, enabling MESFET fabrication on flexible PET substrates. The chemical composition of the Ru-Si-O Schottky metallization was optimized in order to achieve simultaneously a high oxygen content, low resistivity and high optical transmission. The nanostructural studies of the films were performed by means of XRD and TEM. No crystalline phases were recorded in X-ray diffraction patterns. However, high resolution TEM imaging revealed randomly oriented nanocrystalline inclusions embedded in an amorphous matrix. Devices were fabricated on PET foils in top-gate configuration, without neither annealing nor a-IGZO surface treatment. MESFETs exhibit on-to-off current ratio at the level of 1E3 A/A in a voltage range of 2 V, with subthreshold swing equal to 420 mV/dec. Channel mobility of 7.36 cm2/Vs was achieved. This research was in part supported by the Institute of Electron Technology statutory activities.
Authors : D. Caffrey, E. Norton, L. Farrell, C. Smith, I.V. Shvets, K.Fleischer,
Affiliations : D. Caffrey; E. Norton; L. Farrell; I.V. Shvets; and K. Fleischer School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, University of Dublin, Dublin 2, Ireland D. Caffrey Advanced Materials Bio-Engineering Research Centre (AMBER) C. Smith School of Physics Trinity College, University of Dublin, Dublin 2, Ireland
Resume : The capacity to modulate the properties of Transparent Conducting Oxide (TCO) materials is of great importance for the optimisation of device efficiency. Tuning of the refractive index to reduce mismatch between two materials is highly desirable for the reduction of internal interface reflections. Previous works on ZnO:Al have utilised substitution doping with magnesium as a means to alter the bulk refractive index. However, the increased effects of neutral impurity scattering from the randomly distributed Mg leads to a reduction in both the mobility and carrier concentration of the material [1,2]. In our work, we create a superlattice structure of layered conductive amorphous InGaZnO (a-IGZO) and a dielectric material (SiO2) as an alternative method of reducing the refractive index without altering the carrier mobility significantly. These superlattice structures are grown with conventional RF magnetron sputtering from separate IGZO and SiO2 targets.  J. G. Lu; S. Fujita, et al., Appl. Phys. Lett. 89, (2006), 262107  K. Fleischer; E. Arca, et al., Appl. Phys. Lett. 101, (2012), 121918
p-type Transparent Conductive Materials Part 1 : Delfina Muñoz
Authors : İ. Cihan KAYA*, Hasan AKYILDIZ
Affiliations : Department of Metallurgical and Materials Engineering, Sel?uk University, 42075 Konya, Turkey
Resume : Delafossite type oxides have attracted considerable attention due to their unique properties, such as p-type electrical conductivity and transparency in the optical region , which makes them suitable for a variety of optoelectronic applications. In addition, delafossite oxides also showed promising thermoelectric, ozone sensing, photocatalytic hydrogen evolution properties and enhanced cathodic photocurrents in p-type dye-sensitized solar cell applications . Therefore, the synthesis of these oxides in the form of thin films, nanostructured bulk or nanometer size powders is critical for these applications. Among these oxides, Mg-doped CuCrO2 thin film has conductivity up to 220 Scm−1, which is the largest conductivity measured in the A M3 O2 systems . In order to improve functional properties, production of pure and doped CuCrO2 have been demonstrated in the literature using various methods such as conventional solid state synthesis, pulsed laser deposition, sputtering, sol-gel, and hydrothermal approach . Studies on the utilization of wet chemical synthesis-based techniques with flexible sample design showed that a variety of delafossite materials and sample geometries are possible with these approaches instead of using conventional solid state synthesis. Considering of diverse potential applications mentioned above, production of CuCrO2 nanostructures via hydrothermal approach is an alternative method with the added advantage of allowing an easy control of material chemistry and nanometer size particle processing. In this study, pure and Mg-doped CuCr(1-x)MgxO2 (x=0, 0.01, 0.03, 0.05) nanoparticles were synthesized via a well known low temperature hydrothermal method . The effect of Mg concentration on the structural, electrical and optical properties was investigated. The nanoparticles were synthesized via hydrothermal conversion of the reactants at 230 oC for 60 h in a custom made high pressure vessel. The precipitates were collected and cleaned with hydrochloric acid prior to drying. X-ray diffraction study revealed the formation of single phase CuCrO2 for all samples. The crystallite size of the pure sample was estimated to be ~11 nm using Scherrer formula. Electron microscopy examination implied a narrow size distribution for the nanoparticles. In order to understand the effect of Mg-doping on the optical properties of CuCrO2 nanoparticles, ultraviolet-visible spectroscopy was used. UV-Vis measurements revealed that, all nanoparticles exhibit a high transmittance (% 62-68 at 400 nm and % 82-90 at 700 nm) in the optical region. The optical bandgap was found to increase from 3.12 to 3.17 eV as the Mg concentration increases. We have also found that the room temperature electrical conductivity significantly increased with increase in the Mg-content and reached 0.01 Scm-1. Funding for this work was provided by (?YP) Academic Staff Training Program (Project no 2013-?YP-087), and Scientific Research Foundation (BAP) of Sel?uk University (Project no 14401104) which we gratefully acknowledge. 1. A. Stadler, Materials, 5, 661 (2012). 2. J. Ahmed, C.K. Blakely, J. Prakash, S.R. Bruno, M. Yu,Y. Wu and V.V. Poltavets, J. Alloy.Compd. 591, 275 (2014). 3 . R. Nagarajan, A.D. Draeseke, A.W. Sleight and J. Tate, J. Appl. Phys. 89, 8022 (2001). 4 . A.N. Banerjee and K.K. Chattopadhyay, Prog. Cryst. Growth. Ch. 50, 52 (2005). 5. M. Miclau, D. Ursu, S. Kumar and I. Grozescu, J. Nanopart. Res. 14, 1110 (2012).
Authors : Renaud Leturcq, Petru Lunca-Popa, Damien Lenoble
Affiliations : Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg
Resume : In the field of transparent oxide semiconductors, one limitation for producing active devices is the lack of a p-type transparent oxide with good electronic properties. Cu-based delafossite materials are promising candidates, but applications are still hindered by the difficulty to produce it with large scale methods and the still limited electronic performances. Among them, Mg-doped CuCrO2 has shown the highest conductivity with high transparency, but the reported mobility is still two orders of magnitude lower than the expectations. Understanding the conduction properties could lead to the expected improvements for future applications. We have performed electrical measurements on back-gated CuCrO2 thin films in order to investigate the dependence of the conduction properties as a function of the carrier density. Pure CuCrO2 delafossite has been deposited by chemical vapour deposition and checked using X-ray diffraction. The film is deposited on a highly doped Si substrate covered by SiO2 gate oxide through a shadow mask. The conductivity of the thin film decreases when the gate voltage increases, a clear sign of the p-type conduction. From the transverse characteristics we evaluate the hole density at zero gate voltage to 6E18 cm-3, and the field effect transistor mobility of 0.04 cm2/Vs at room temperature. In order to understand the limitation of the mobility, we have further measured the transport properties as a function of temperature while varying the hole density.
Authors : Elisabetta Arca, Daragh Mullarkey, Igor Shvets
Affiliations : School of Physics and CRANN, Trinity College Dublin, Dublin, Ireland
Resume : p-type transparent conductors and semiconductors are still suffering from remarkably lower electrical performance in comparison with their more widely spread n-type counterparts. In this contribution we will present a comparative study on the defect chemistry of doping Cr2O3. Thin films of Cr2O3 doped with Zn, Mg, or Ni were deposited by Pulsed Laser Deposition. Conductivity as high as 20 S/cm were reproducibly achieved by Ni-doping, which represents an improvement of more than an order of magnitude in comparison to the conductivities previously reported for doped Cr2O3. A comprehensive characterization on the structural properties by X-ray Diffraction, on the electronic properties by X-ray Photoelectron Spectroscopy and on the electrical properties by DC resistance measurements have allowed us to shed some light on the mechanism responsible for the improvement.
Authors : J. Ramírez-Castellanos1, M. Taeño1, F. del Prado2, M. García-Tejedor2, D. Maestre2, A. Cremades2, J. Piqueras2 and J. González-Calbet1
Affiliations : 1 Dpto. de Química Inorgánica, Fac. de Químicas, Univ. Complutense de Madrid, 28040, Madrid, Spain. 2 Dpto. de Física de Materiales, Fac. de Físicas, Univ. Complutense de Madrid, 28040, Spain.
Resume : SnO2 is one of the most investigated semiconducting oxides due to its versatility and widespread applications in catalysis, gas sensing, photovoltaics, the chemical industry, energy storage, or as an alternative anode material  because of its high Li storage capacity. As most of these applications are highly dependent on the dimensions and the presence of dopants, during the last few years increasing research has been focused on the synthesis and study of SnO2 nanostructures doped with different elements, in order to optimize the response of SnO2. Different approaches are considered in order to solve problems such as the SnO2 volume expansion during charge/discharge processes, as the use of nanostructured SnO2 . In this work, different SnO2 based compounds have been prepared and characterized, with special interest focused on the effects induced by Li doping. Therefore, nanoparticles, rods and tubes have been fabricated following different methods. SnO2 nanoparticles doped with Li have been synthesized via a modified Pechini method, based on the use of polymeric precursors, which allows reaching high control in size and composition Moreover, low dimensional doped SnO2 structures in forms of nanowires and microtubes have been grown at 800-1400 ºC by a catalyst free evaporation-deposition method using either metallic Sn or SnO2 mixed with Li2CO3 as starting materials. The Li effect on the microstructure and luminescent properties of cassiterite SnO2 nanoparticles, nanowires and microtubes is studied by means of transmission electron microscopy (TEM), cathodoluminescence (CL), energy dispersive x-ray spectroscopy (EDS) and Raman spectroscopy. The thermal parameters and the corresponding precursor determine the morphology of the as-grown structures which dimensions vary from 5 nm to tens of microns width and up to hundreds of microns length. The incorporation of Li in SnO2 and its influence on the luminescence properties has scarcely been studied in nano and microstructures. The Li doping causes an enhancement of the conductivity of the samples. References:  Y.D. Ko, J.G. Kang, J.G. Park, S. Lee, D.W. Kom, Nanotechnology, 20, 455701 (2009)  J.Y. Huang, L. Zhong, C.M. Wang, J.P. Sullivan, W. Xu, L.Q. Zhang, S.X. Mao, N.S. Hudak, X.H. Liu, A. Subramaniam, H. Fan, L. Qi, A. Kushima, J. Li. Science, 330, 1515 (2010)
Authors : K. Elen, H. Damm, A. Kelchtermans, K. Schellens, A. Hardy, M. K. Van Bael
Affiliations : Hasselt University, Institute for Materials Research (IMO), Inorganic and Physical Chemistry, and IMEC vzw, division IMOMEC, Martelarenlaan 42, 3500 Hasselt, firstname.lastname@example.org
Resume : Aluminium doped zinc oxide (AZO) has attracted significant attention for replacing ITO. In the current work two approaches are presented for the wet-chemical processing of AZO. Chemical solution deposition of aluminium doped zinc oxide, by spin coating a 2-butoxyethanol precursor, yields TCO coatings with a transparency higher than 90 % and a resistivity of 1.3 mOhm cm after annealing at 450 °C in a reducing atmosphere. Furthermore, the potential of this precursor for large area coatings is demonstrated, by transferring the precursor to a spray coating system. Next, different synthesis routes for AZO nanoparticles are presented leading to particles with various characteristics. Minor modifications of the synthesis conditions have a profound impact in the particle morphology, the crystallographic position of the aluminium dopant and the generation of free charge carriers. Through an in-depth study of their characteristics, the most promising particles can be selected. Also, their potential as building blocks for transparent conducting coatings is demonstrated, providing a resistivity of 9.4 mOhm cm. In this work we demonstrate that through in-depth characterization we can correlate the synthesis conditions to the intrinsic properties of the obtained oxide, and come to functional, solution deposited TCO coatings. Acknowledgement: The presented research is conducted in the frame of the SoPPoM program and is financially supported by the Strategisch Initiatief Materialen (SIM).
Authors : D. Casotti1, A. di Bona2, S. Valeri1 2,
Affiliations : 1 Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, via Campi 213/a, 41125 Modena, Italia; 2 Centro S3, Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, via Campi 213/a, 41125 Modena, Italia.
Resume : Nb-doped anatase TiO2 was shown to be a viable candidate for replacing indium-tin-oxide as a transparent electrode in several technological applications, like flat panel displays, thin film amorphous silicon solar cells or dye-sensitized solar cells. Transparent conducting Nb-doped anatase TiO2 films were grown at high rate by reactive DC magnetron sputtering from metal targets, using an active control of the oxygen gas flow in order to stabilize the plasma discharge voltage and to control the films stoichiometry. Electric transport and electronic properties of the highly conductive film are studied as a function of several process parameters, like plasma voltage, doping level and post-deposition reductive annealing temperature profile. Exposure of the films to ambient air, even at room temperature, either before or after the thermal process, has been found to play a crucial role in determining the resistivity of the material. In particular, air exposure times in the minutes range increases the resistivity of the film by one order of magnitude or more. Partial rejuvenation of the material could be obtained by thermal treatment.
Authors : E. Chubenko (1), V. Bondarenko (1), M. Balucani (2)
Affiliations : (1) Belarusian State University of Informatics and Radioelectronics, P. Brovka str. 6, Minsk 220013, Belarus; (2) Universita La Sapienza di Roma, Via Eudossiana 18, Roma 00184, Italy
Resume : ZnO nanostructures are useful element of perspective photovoltaic devices. ZnO nanostructures arrays can be used in thin film solar cells, photoelectrochemical cells and tandem solar cells. One of the key advantages of ZnO over other comparable wide band-gap semiconductors is that it can be deposited by the simple techniques of electrochemical and chemical deposition in the form of nanostructures arrays. ZnO is also can be easily doped directly during the deposition process by addition of corresponding additives to the solution. In this work we studied the electrochemical and chemical hydrothermal deposition of undoped ZnO and doped ZnO:Al and ZnO:Er nanostructures. The influence of temperature, solution composition, current density (in the case of electrochemical deposition), substrate conductivity and pH on the morphology and composition of deposited ZnO nanostructures were studied. Obtained doped ZnO nanostructures arrays showed enhanced conductivity compared to undoped ZnO and additional absorption bands in the IR range related to the presence of Er atoms in the ZnO crystal lattice. Their applications as a transparent conductive electrodes and energy upconversion layers are also discussed. This work is supported by Belarus Government Research Programs Crystalline and molecular structures, grant 1.09, Electronics 2015, grant 1.2.08 and Belarusian Republican Foundation for Fundamental Research grant X14MB-009.
Authors : Bongkyun Jang, Chang-Hyun Kim, Jae-Hyun Kim, Kwang-Seop Kim, Hak-Joo Lee, Byung-Ik Choi
Affiliations : Department of Nano-Mechanics, Korea Institute of Machinery and Materials
Resume : Graphene has outstanding physical properties that make it attractive for a variety of applications using excellent electrical, optical, mechanical properties. Among them, flexible and transparent electrode is one of the most promising applications. For a lot of applications for transparent electodes like solar pannel, touch screen, graphene should be transferred on the substrates with various materials, surface morphorlogies, surface energy and surface roughness. Transferring large area graphene sysnthesized on copper substrate by CVD process, is optimized by roll to roll transfer process. This process has advantages for the scailability and the compatibility for other roll process. In addition, graphene can be transferred on various substrate by roll transfer process. We used the carrier film for a protection of graphene film during copper substrate etching, handling, and transferring process. And finally it was transferred on various substrate like PET, silicon, and other polymer substrates. We compared to the qualities of graphene transferred on various substrates, and evaluated the effect of substrate. These results will be able to be directly used for fabrication of the devices with graphene transparent electrodes.
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Metallic Nanowires or Nanoparticles Part 2 : Benjamin Wiley
Authors : John J. Boland
Affiliations : School of Chemistry and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Ireland
Resume : The seminar will discuss scaling and evolution of connectivity in inorganic nanowire networks exposed to different stimuli. Network junctions control the overall properties of any network and we show that all networks evolve connectivity in specific ways. In particular, we describe how junctions evolve from capacitor-like to resistor-like barriers in response to an applied stimulus and how the network self-selects connectivity paths by choosing the lowest barrier junctions. Continued stressing causes the selected junctions to strengthen and ultimately co-opts neighbouring junctions to reinforce the overall response to the stimulus. By engineering these junctions it is possible to control the properties and response of the network. Transparent materials with arbitrarily controlled connectivity and conductivity are demonstrated as are device with arbitrarily controlled multi-level memory, and single junctions capable of a learning response.
Authors : Albert de Jamblinne de Meux, Geoffrey Pourtois, Jan Genoe, Paul Heremans
Affiliations : KU Leuven, ESAT, B-3001 Leuven, Belgium , imec, Kapeldreef 75, B-3001 Leuven, Belgium; imec, Kapeldreef 75, B-3001 Leuven, Belgium; imec, Kapeldreef 75, B-3001 Leuven, Belgium; KU Leuven, ESAT, B-3001 Leuven, Belgium, imec, Kapeldreef 75, B-3001 Leuven, Belgium;
Resume : Amorphous Indium-Galium-Zinc-Oxyde (a-IGZO) is a promising semiconducting material for large area electronics applications, displays and imagers. It combines both a sizable mobility, a good stability and a very low off current compared to conventional amorphous silicon (a-Si). However, little is known on its fundamental properties and how they could be potentially engineered. In this paper, the electronic properties of stoichiometric and defective a-IGZO will be investigated using first-principles simulations. An emphasis will be set on the statistical distribution of the energetic and of the electronic signatures of neutral and charged oxygen vacancies. In opposition to the results reported in literature, we find that oxygen vacancies do not always display a negative-U behavior but can rather adopt a smoother charge transition. Also, a non-negligible number of vacancies (~50 %) does not induce defective states in the band gap. We will illustrate that this difference with respect to previous works, is bound to the limitations of the dimensions of the models used. Finally, we will show that some oxygen vacancies adopt a meta-stable behavior upon charge loading due to the complexity of the energetic landscape built during the amorphization process.
Authors : Andrej Čampa1, Marko Berginc1, Katarina Vojisavljević2, Barbara Malič2, Peter Panjan2, Marko Topič1
Affiliations : 1 University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Photovoltaics and Optoelectronics, Traka cesta 25, 1000 Ljubljana, Slovenia 2 Joef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
Resume : In the optoelectronics, especially in thin-film photovoltaics, the transparent conductive oxides (TCO) play an important role to minimize the front contact optical losses. The TCOs used as a front contact needs to have low resistivity (<1 mOhmcm), high optical transparency in the broad wavelength region (>80% at 400-1000 nm) and high temperature stability. In the case of using nano-imprinted lithography for reproduction of the morphologies the good electrical and optical properties should be obtained at low deposition or post-annealed temperatures. To translate the morphology, at which the light is efficiently scattered, to the internal interfaces of the solar cells very low thickness of TCO is required (<200 nm). One of such candidates is Ga doped SnO2:In (ITO), which exhibits better optical and similar electrical properties to ITO 90/10, additionally it has lower indium content. A multicomponent Ga-In-Sn oxide target with Ga:In:Sn = 4:64:32 metal ratio was prepared, that was used in RF sputtering system for deposition of high quality GITO thin-film layers on glass. In this study, we will focus on electrical (specific resistivity, mobility and carrier concentration) and optical properties (thickness and refractive index) as a function of deposition and annealing parameters. The results of optical and electrical characterization of the two best GITOs will be presented, one globally optimized and one optimized with the respect to the low temperature deposition prerequisite.
Authors : Yi-Ting Lai, Nyan-Hwa Tai
Affiliations : Department of Materials Science and Engineering, National Tsing-Hua University
Resume : This work demonstrates a one-step process to synthesize uniformly dispersed hybrid nanomaterial containing silver nanowires (AgNWs) coated with p-type reduced graphene (p-rGO). The hybrid nanomaterials were coated onto a polyethylene terephthalate (PET) substrate for preparing high performance flexible transparent conductive films (TCFs). The p-rGO plays the role of bridging discrete AgNWs, which provides more electron holes and lowers the resistance of the contacted AgNWs; as a result enhancs the electrical conductivity without sacrificing too much transparence of the TCFs. Additionally, the p-rGO also improves the adhesion between AgNWs and substrate by covering the AgNWs on substrate tightly. The study also shows that coating of the hybrid nanomaterials on the PET substrate demonstrates exceptional optoelectronic properties with a transmittance of 94.68% (at a wavelength of 550 nm) and a sheet resistance of 25.0 Ω/sq; furthermore, no significant variation in electric resistance can be detected even the film was subjected to a bend loading with a radius of curvature of 5.0 mm or the film was loaded with a reciprocal tension or compression for 1000 cycles. The study shows that the fabricated flexible TCFs have the potential to replace indium tin oxide film in the optoelectronic industry.
Authors : Çağla Çetin, Hasan Akyıldız*
Affiliations : Department of Metallurgical & Materials Engineering, Selçuk University, Konya, 42075, Turkey
Resume : Delafossite type oxides including CuCrO2 have attracted considerable attention due to their unique properties, such as p-type electrical conductivity and transparency in the optical region . This provides the opportunity to use n-and p-type TCOs together to develop all transparent p-n junctions which can be utilized in many optoelectronic applications. Delafossite oxides also showed promising thermoelectric, ozone sensing, photo-catalytic hydrogen evolution properties and enhanced cathodic photocurrents in p-type dye-sensitized solar cell applications . Among these oxides, Mg-doped CuCrO2 has a conductivity up to 220 Scm−1, which is the largest conductivity measured in the A+M3+O2 systems . Studies on the utilization of wet chemical synthesis-based techniques with flexible sample design showed that a variety of delafossite materials and sample geometries are possible with these approaches instead of using conventional solid state synthesis. Recently, it was shown that delafossite oxides could successfully be synthesized via electrospinning [4,5]. Chiun and Chen, reported on the formation of single-phase CuCrO2 wires having 434 nm diameter with vacuum annealing at 700 °C for 20 min . Considering of diverse potential applications such as optoelectronic devices, sensor and catalysis applications, production of CuCrO2 nanostructures via electrospinning is an alternative method with the added advantage of allowing an easy control of material chemistry with various morphologies. This study aims to understand the fundamentals of the formation mechanism of CuCrO2 in the form of nanofibers. By the investigation of the effect of time, temperature and annealing atmosphere on the formation of single phase material, the study expects to reveal a correlation between the phase purity, size, microstructure, and optoelectronic properties for specific applications. For this purpose appropriate amounts of copper chloride, chromium nitrate and polyvinylpyrrolidone were mixed in water to obtain a viscous solution. The solution was transferred on an aluminum foil substrate in the form of nanofibers, via electrospinning method. All samples were collected at room temperature with 0.3 mL/h feeding rate under an applied voltage of 16 kV. Collected fibers were annealed under two different conditions; namely isochronal and isothermal. Isochronal experiments involved heating from room temperature to various temperatures, i.e., 400, 500, 600, 650 and 700 °C under high purity flowing nitrogen gas in a tube furnace and holding the samples at relevant temperature for 1 h. Isothermal experiments were carried out at temperatures of up to 700 °C. This involved heating the furnace to a selected temperature and loading of the sample for certain durations, i.e. 15, 30, 45 and 60 min. According to X-ray diffraction measurements, with isochronal annealing, the formation of CuCrO2 phase starts at 500 °C and at least 700 °C is necessary to obtain single phase material. Scanning electron microscopy examinations revealed the formation and coarsening of plate-like grains with increasing annealing temperature. Due to this, the fiber structure was completely disappeared after heat treating the fibers at 700 °C for 3 h. To preserve the nanofiber structure and prevent coarsening, isothermal annealing experiments were performed at 700 °C. In summary, it was shown that CuCrO2 nanofibers could successfully be synthesized via isochronal and isothermal annealing of electrospun polymer/metal composite fibers. We have found that isothermal annealing at 700 °C for 1 h in flowing nitrogen atmosphere leads to the formation of a refined structure while preserving the nanofiber morphology. We have also carried out measurements on the structural, morphological, optical and electrical properties of the fibers. Support for this work was provided by TUBITAK MAG (Project no 214M410),and Scientific Research Foundation (BAP) of Selçuk University (Project no 15201028) which we gratefully acknowledge. 1. References  F. A. Benko, F. P. Koffyberg, J. Phys. Chem. Solids, 45, 1984, 57-59.  A.N. Banerjee, K.K. Chattopadhyay, Prog. Cryst. Growth Charact. Mater. 50, 2005, 52-105.  R. Nagarajan, A.D. Draeseke, A.W. Sleight, J. Tate, J. Appl. Phys., 89, 2001, 8022-8025.  S. Zhao, M. Li, X. Liu, G. Han, Mater. Chem. Phys., 116, 2009, 615-618.  T. Chiun, Y. Chen, Cer. Inter., 41, 2015, doi:10.1016/j.ceramint.2015.03.224.
Transparent Conductive Oxides Part 4 : Thomas Riedl
Authors : Junjun Jia and Yuzo Shigesato
Affiliations : Graduate School of Science and Engineering, Aoyama Gakuin University
Resume : Recently, transparent conducting oxide films that contain a reduced amount or no indium are of considerable research interest as alternative materials for Sn doped In2O3 (ITO) transparent electrode in optoelectronic applications. Here, we discussed the structure, optical and electrical properties for amorphous In2O3-ZnO (IZO) and polycrystalline Al doped ZnO (AZO) thin films as next generation transparent electrode. The structure of IZO films can be easily tailored from amorphous to polycrystalline states by changing the sputtering deposition conditions, indicating the possibility to produce the film without internal stress between the film and flexible substrate for flexible devices. Amorphous IZO films has the similar optical bandgap to ITO films, and hard x-ray photoemission spectroscopy measurements for IZO films with various carrier densities show the existence of the bandgap narrowing effect in amorphous IZO films. We also investigated the optical bandgap and work function in polycrystalline AZO films. The optical band gap and work function showed the positive and negative linear relationships with the two-thirds power of carrier density, respectively, which are explained by Burstein-Moss effect considering nonparabolic conduction band. We also discussed the carrier transport mechanism of IZO and AZO films in detailed.  J. Jia, Y. Shigesato et. al, J. Appl. Phys., 113, 163702 (2013), J. Appl. Phys., 112, 013718 (2012), Appl. Phys. Express, 7, 105802 (2014).
Authors : Mandeep Singh, Maria Magliulo, Kyriaki Manoli, Mohammad Yusuf Mulla, Maria Vittoria Santacroce, Cinzia Di Franco, Gaetano Scamarcio, Gerardo Palazzo, Luisa Torsi
Affiliations : Dipartmento di Chimica, Universita degli Studi di Bari Aldo Moro, Bari, Italy-70126 CNR-IFN and Dipartimento Interateneo di Fisica University of Bari "Aldo Moro", Bari, Italy-70126
Resume : Solution processed metal-oxides based electronic devices have attracted great deal of attention during the past few years for their potential use in next generation transparent optoelectronic devices. They have high charge-carrier mobility, high optical transparancy and excellent chemical/mechanical stability. Among the metal oxide, ZnO has a wide band gap (3.37 eV), non-toxic and environmentally stable, biocompatible, biodegradable and, at the same time, is made of zinc that is among the most abundant elements in earth's crust. Recently solution processed ZnO thin-films and nano-rods have been successfully implemented as active layers in a number of different electrolyte gated TFT configurations. We are presenting a solution processed electrolyte gated ZnO based TFT. ZnO thin films were prepared with the sol-gel spin coating method. The ZnO structure has been assessed by XRD, XPS and Raman spectroscopy. The gating of the transistor has been performed with water, Posphate Baffered saline and ionic liquids. Impedance spectroscopy has been performed to measure the capacitance of the ionic liquids. The devices gated with ionic liquid shows very high drain current with mobility as high as 4.7 cm2/Vs and Ion/Ioff ratio in the order of 103. The water gated devices was further used for biofunctionalization of ZnO active channel layer and have potential to be used for biosensing applications.
Authors : G. Bonneux (1), K. Elen (1), E.J. van den Ham (1), W. Marchal (1), J.P. Locquet (2), M. Seo (3), A. Hardy (1), M.K. Van Bael (1)
Affiliations : (1) Hasselt University, Institute for Materials Research (IMO), Inorganic and Physical Chemistry, and IMEC vzw, division IMOMEC, Martelarenlaan 42, 3500 Hasselt; (2) KU Leuven, Dept. Physics & Astronomy, Celestijnenlaan 200D, 3001 Leuven, Belgium; (3) KU Leuven, Dept. Materials Science, Kasteelpark Arenberg 44, 3001 Leuven, Belgium
Resume : The last decade has seen an increased attention towards the implementation of InGaZnO (IGZO) as a metal oxide channel material in TFT-devices. Crystalline IGZO shows a high electron mobility and low off-state leakage current, which results in an improved device performance compared to amorphous IGZO [Yamazaki et al., Jpn. J. Appl. Phys. 53 (2014)]. Thin film deposition of the IGZO superlattice structure requires a good layer homogeneity in addition to control of the stoichiometry, which can be achieved by using a solution-based process. In practice, this is usually achieved using 2-methoxyethanol (2-ME) based precursors. However, due to its harmful and teratogenic properties, alternative solvents are being explored. In this work, an aqueous precursor system is developed, in which the metal ions are stabilized by α-hydroxy carboxylic acids as ligands. By spray-coating this precursor, dense and uniform layers are deposited. Through an optimized multi-step thermal treatment, crystalline thin films of IGZO are obtained that show a preferential c-axis orientation after rapid thermal annealing at 1000°C in inert conditions. Preliminary electrical characterization of the deposited thin films already shows promising resistivities of around 8 mΩ*cm, which can apply to several areas of interest. Acknowledgements: This research is financially supported by the Research Foundation-Flanders (FWO Vlaanderen, project nr. G054312N). We thank Y.Guo, P.Homm, M.Menghini for characterization.
Authors : Andriy Lyubchyk, Antonio Vicente, Bertrand Soule, Tiago Mateus, Andreia Araujo, Manuel J. Mendes, Hugo Aguas, Elvira Fortunato and Rodrigo Martins
Affiliations : CENIMAT/I3N, Departamento de Ciencia dos Materiais, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa (FCT-UNL), and CEMOP-UNINOVA, 2829-516 Caparica, Portugal.
Resume : The increasing demand of transparent conducting oxides (TCO) materials for optoelectronic devices  has turned into a worldwide multi-billion economy that nowadays depends on the availability of ITO [ ]. Global ITO sputtering targets demand is 1,400 tons (2014) and it will increase up to 2,500 tons by 2016. However, In is a rare and expensive material, hence, there is a critical need to replace ITO with reliable alternative TCOs made of abundant compounds. The post-deposition modification of ZnO-based TCOs can be the key to produce thin films with optoelectronic properties similar to ITO and at a lower cost. Here, we present our findings for post-deposition annealing enhancement of AZO, AZOH, GZOH and ZnOH deposited by RF sputtering at room temperature. These studies comprise results of thermal annealing at atmospheric pressure, vacuum, forming gas, H2 and Ar atmospheres and H2 and Ar plasma, which lead to significant improvements of the optical, morphological and electrical properties. The post-deposition annealing leads to a gain in resistivity above 20% for AZO, AZOH and GZOH, reaching ρ≈2.4?10-4, while ZnOH showed a smaller gain of 7%. The averaged optical transmittance in the visible region is about 85% for the investigated TCOs. Such results match the properties of state-of-art ITO (ρ≈10-4 and transmittance in VIS range of 90%). 1 Antonio Vicente et al, J. Mater. Chem. A, 2015; DOI:10.1039/C5TA01752A 2 TCC: Technologies & Global Markets, AVM105A, 2014
Authors : J. Ram?rez-Castellanos1, G. C. V?squez2, M. A. Peche-Herrero1, D. Maestre2, A. Cremades2, J. Piqueras2 and J. M. Gonzalez-Calbet1
Affiliations : 1 Dpto. de Qu?mica Inorg?nica I, Facultad de Qu?micas, Univ. Complutense de Madrid, 28040, Madrid, Spain 2Dpto. de F?sica de Materiales, Facultad de F?sicas, Univ. Complutense de Madrid, 28040, Spain.
Resume : The efficiency of TiO2 is strongly dependent on the ability to control the morphology and crystal size, defects, doping and also its crystallographic phase, which plays a key role in the functionalization of this material. TiO2 crystallizes in three polymorphs: anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic), being anatase and rutile the most investigated and extensively used so far. The characteristic physical and chemical properties associated to rutile and anatase phases, i.e. different bandgap, surface energy, dielectric constant, refractive index or mechanical properties, among others, make them specifically suitable for different applications. The anatase to rutile transition (ART) is not totally understood so far, and several issues still require to be addressed. In this work, locally promoted ART and micropatterning based on titania polymorphs have been achieved by means of controlled laser irradiation on doped (Al, Fe) TiO2 nanoparticles synthesized by a modified Pechini method. This method allows us to obtain high homogeneity in size and composition for the doped anatase TiO2 nanoparticles, for which high dopant (Al, Fe) cationic concentration were obtained avoiding phase segregation . Control of the anatase to rutile transition was achieved by laser irradiation and the kinetic of this process has been studied as a function of the dopant and the irradiation conditions . Raman and PL results demonstrate that the ART can be either inhibited or promoted by doping with Al or Fe, respectively. The higher the concentration of Fe in the anatase TiO2 nanoparticles, the faster the phase transformation evolves. Stabilization of anatase due to the presence of Ti3 at the surface of the nanoparticles, reduction of Fe3 to Fe2 involving oxygen deficiency during laser irradiation and formation of rutile starting at the surface of the nanoparticles have been found to influence the ART process. HRTEM results point out to the relevance of the presence of twins in the formation of rutile phase by laser irradiation. An improvement in the control of the ART has been described, as compared with other methods, such as thermal annealing for which micrometric control of local ART is not achieved. The possibility of achieving an ART micrometric patterning has been demonstrated , thus facing challenging performances of this material.  G. C. V?squez, M.A. Peche-Herrero, D. Maestre, A. Cremades, J. Ram?rez-Castellanos, J.M. Gonz?lez-Calbet, J. Piqueras. J. Phys. Chem. C, 117, 1941, (2013)  OEPM Patent P201400722, (2014) and OEPM Patent P201400759, (2014)  G. C. Vasquez, A. Peche-Herrero, D. Maestre, A. Gianoncelli, J. Ram?rez-Castellanos, A. Cremades, J. M. Gonzalez-Calbet and J. Piqueras, J. Phys. Chem C (in press).
Authors : A. Vlad1, R. Birjega1, A. Matei1, V. Ion1, M. Dinescu1, R. Zavoianu2
Affiliations : 1National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Str., 77125 Bucharest- Magurele, Romania 2University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and Catalysis, 4-12 Regina Elisabeta Bd., Bucharest, Romania
Resume : The preparation of photofunctional hybrid thin films of intercalated chromophores in Layered double hydroxides (LDH) matrix by pulsed laser deposition (PLD) is investigated, and the functionality of the films will be examined through the optical properties introduced by the chromophore. An interesting class of chromophores is coumarins and coumarins derivates. Two systems will be studied: coumarin intercalated in MgAl-LDH and coumarin and dodecyl sulfate (DS) co-intercalated in MgAl-LDH. The introduction into the LDH gallery of a second anion, dodecyl sulfate anion aimed the suppression of the aggregation of chromophore anions. X-ray diffraction, infrared spectroscopy and UV-vis spectroscopy were the techniques used for the investigation of the functional hybrid targets and the as prepared films. The effect of the deposition condition, primarily of the laser wavelength on the optical properties of the photofunctional coumarine intercaleted - LDH films was examined.
Authors : E. Norton, L. Farrell, D. Mullarkey, I.V. Shvets and K. Fleischer
Affiliations : Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and School of Physics, Trinity College Dublin, Dublin 2, Ireland
Resume : Thin films of p-type Cr2O3:Mg have been produced by Molecular Beam Epitaxy (MBE) as well as amorphous p-type CuCrO2 deposited by a low temperature solution based method (spray pyrolysis). These thin films are deposited on top of a n-type Indium Tin Oxide substrate creating transparent pn junctions. The band alignment of these two interfaces is studied using X-ray Photoelectron Spectroscopy (XPS) and Ultra Violet Photoelectron Spectroscopy (UPS). An estimate of the band discontinuities at the interfaces of ITO/ Cr2O3:Mg and ITO/a- CuCrO2 are given. An emphasis is given to the fact that the Fermi level and work function position for both Cr2O3:Mg and a-CuCrO2 show changes with surface preparation and surface termination.
Authors : M. Duta1, L.Predoana1, S.Preda1, P.Osiceanu1, M.Nicolescu1, M.Gartner1, M.Zaharescu1, S. Simeonov2, D. Spasov2, P.Terziyska2, A. Szekeres2
Affiliations : 1Institute of Physical Chemistry Ilie Murgulescu, Romanian Academy 202 Splaiul Independentei, 060021 Bucharest, Romania; 2Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria
Resume : Titanium dioxide has found a wide application in novel environment- and energy-related processes such as photocatalysis for water purification, gas sensing, etc. Adding Nb or V dopants improves its electrical conductivity without decreasing its visible transmittance what makes it promising for TCO applications. The role of generation and transformation of point defects by technological processes in the electrical conduction mechanism is important for TiO2:Nb(V) film application. We report on TiO2 multilayers deposited on glass and Si substrates by the sol-gel method, focusing on the influence of 1.2 at.% Nb(V) doping on the structure of the films and their optical and electrical properties. The TiO2:Nb(V) films crystallized in anatase phase as evidenced by XRD analyses. XPS measurements revealed that Nb(V) dopants segregated from bulk to the surface. The transmittance values were around 80 % in the 400- 900 nm visible range of light. Electrical measurements of the I-V and C-V characteristics of MIS structures with the TiO2:Nb(V) films pointed out that the doping level in the films had be equal or greater than 10^16 cm^-3. The character of I-V dependences and decrease of the specific resistivity (10^4-10^5 Ohm.cm) by increasing the electrical field evidenced for bulk character of electrical conduction in the TiO2:Nb(V) films and revealed that the current through the films is space charge limited current via deep levels with energy distribution in the energy gap of TiO2.
Authors : J. Resende1,2, N. D. Nguyen2, J. L. Deschanvres1
Affiliations : 1 Laboratoire des Mat?riaux et du G?nie Physique, Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France; CNRS, LMGP, F-38000 Grenoble, France 2 Department of Physics, Universit? de Li?ge, Belgium
Resume : Oxide electronics is an important emerging area, notably for the development of transparent thin film transistors (TFTs) and other complex electronic circuits. The successful application of n-type oxides to TFTs has motivated the interest in p-type oxide based semiconductors, also to be applied to TFTs or to complementary metal-oxide semiconductor (CMOS) technology. However, until now there is a lack of p-type oxide semiconductors with performance similar to that of n-type oxide. Among the different metallic oxides, Cu (I)-based oxides exhibit one of the lowest ionic character. These compounds are therefore one of the most promising candidates as p-type transparent semiconductors.Nevertheless, the band gap of 2,17eV is modest for transparent electronics applications, since the transmittance of Cu2O films is low on the visible part of the light spectrum. The incorporation of cations with large radii than Cu has been proposed as a way to achieve a higher band gap, by diminishing of three-dimensional Cu-Cu interactions, only possible with larger cations than Cu . Therefore, cation doped Cu2O thin films were grown by metal-organic chemical vapor deposition (MOCVD). The three doping elements studied (Sr2 , Sn2 and La3 ) were selected having in account theoretical predictions for the band structure and the deposition conditions of Cu2O. The study focus on thin films growth optimization combined with electronic transport analysis and optical transmittance measurements.
Authors : Petru Lunca Popa, Jonathan Crepeliere, Renaud Leturcq and Damien Lenoble
Affiliations : Materials Research and Technology Department (MRT), Luxembourg Institute of Science and Technology (LIST), L-4422 Belvaux, Luxemburg
Resume : CuxCryOz thin-films are grown via a DLI-MOCVD (Direct Liquid Injection - Chemical Vapour Deposition) process for the substrate temperature range of [400-650oC], different precursors concentrations and at different oxygen partial pressure. Electrical and optical properties of thin films, and the influence of depositions parameters on these properties are deeply investigated. The as-deposited films present a medium degree of crystallinity, a good transmission up to 80% in the visible range with a corresponding band gap around 3.2 eV, making such films particularly appealing for transparent electronics applications. Electrical conductivity values up to 30 S/cm were measured. Thermal activation energies are in range of hundreds of meV, strongly influenced by the oxygen partial pressure. The crystallinity of the films is improved by increasing the precursor concentration and by tailoring substrate temperatures. No influence of the oxygen partial pressure on to crystallinity was observed. The band gap can also be tuned by adjusting the precursors concentration, the oxygen partial pressure and the substrate temperature. The conduction mechanisms are also studied and significant shifts in the activation energy of the conductivity are evidenced. Various hypotheses in terms of dopants, defects, crystallinity and polarons are discussed to interpret the conduction mechanisms of holes.by change in the polaron hopping mechanism.
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Authors : Taras Radchenko, Valentyn Tatarenko, Igor Sagalianov, Yurij Prylutskyy
Affiliations : Institute for Metal Physics, N.A.S.U., 36 Acad. Vernadsky Blvd., Kyiv, Ukraine; Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., Kyiv, Ukraine
Resume : The electron-transport properties of adatom-graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. Potassium adatoms in monolayer graphene are modeled by the scattering potential adapted from the independent self-consistent ab initio calculations. The results are obtained numerically within the framework of quantum-mechanical Kubo-Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. These the correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms.
Transparent Conductive Oxides Part 5 : Joris Proost
Authors : Thomas Riedl
Affiliations : Institute of Electronic Devices, University of Wuppertal, Wuppertal, Germany
Resume : Today, ITO is the most frequently used transparent electrode material. The limited abundance of Indium is expected to cause severe issues. In my presentation I will discuss two possible alternatives. Firstly, a hybrid approach based on a composite of a mesh of silver nanowires and a conductive metal-oxide will be demonstrated. Here, SnOx or Al:ZnO prepared at low-temperatures (100°C) will be used to fuse the wires together and also to "glue" them to the substrate. The resulting electrodes show a low sheet resistance (5.2 Ohm/sq) and high average optical transmission of 87%. Their application as transparent top-electrodes semitransparent organic solar cells will be shown. In the second part, I will introduce the first robust transparent electrodes which are at the same time gas diffusion barriers (GDBs). Generally, GDBs are inevitable to protect sensitive organic devices against ambient gases. Transparent and electrically conductive GDBs (TCGDBs) could serve as electrode and moisture barrier simultaneously. As of yet, work on TCGDBs is very limited. TCGDBs based on ZnO suffer from the severe degradation of their electrical conductivity by orders of magnitude upon exposure to damp heat conditions after very short time. We will show that these issues can be overcome by the use of tin oxide (SnOx) grown by ALD. Robust conductivities of up to 300 S/cm and extremely low water vapor transmission rates (WVTR) on the order of 10-6 g/(m2 day) can been achieved.
Authors : L. Farrell , E. Norton , B.J. ODowd , D. Caffrey, I.V. Shvets, and K. Fleischer
Affiliations : L. Farrell ; E. Norton ; B.J. ODowd ; D. Caffrey; I.V. Shvets; and K. Fleischer : School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, University of Dublin, Dublin 2, Ireland D. Caffrey; Advanced Materials Bio-Engineering Research Centre (AMBER)
Resume : p-type transparent conducting materials are sought after for optoelectronic devices. Little work has been done on low cost synthesis of these materials for large area flexible substrates. In this contribution a low temperature (≈ 345°C) growth method for CuCrO2 is demonstrated by spray pyrolysis using metal-organic precursors. Smooth films were grown on glass substrates with a highest conductivity of 10 S/cm. The most conductive samples are transparent enough to have figure of merits as high as 390 μS. Remarkably despite the low crystallinity of the films, properties comparable with crystalline CuCrO2 are observed. Mobilities of the films are estimated to be 5×10-3 cm2/Vs using the small polaron hopping model. No post-annealing of the films is required in contrast to previous reports. The ability to form material at lower temperatures greatly improves prospects for applications. As this is a solution based technique it is more attractive to industry as PVD methods are slow and costly in comparison.
Authors : Emma Norton, Leo Farrell, David Caffrey, Stephen Callaghan, Cormac McGuinness, Igor Shvets, Karsten Fleischer
Affiliations : Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and School of Physics, Trinity College Dublin, Dublin 2, Ireland
Resume : The valence band structure of novel p-type transparent oxides crystalline Cr2O3:Mg and amorphous CuCrO2 is analysed as a function of incoming photon energy. By analysing the valence band photoemission data across the Cr 3p-3d, Cu 3p-3d, and Mg 2p-3s transitions the contributions of Cu and Cr d-states and Mg s-states to the valence band structure is evaluated. The valence band of both p-type TCOs show striking similarities to measurements on crystalline CuCrO2, highlighting the importance of the Cr-O octahedra on the electronic states at the top of the valence band.
Authors : S. Agnello1*, A.Piazza1,2,3, G. Buscarino1, G. Fisichella2, A. La Magna2 , F. Roccaforte2, M. Cannas1, F.M. Gelardi1, F. Giannazzo2
Affiliations : 1Department of Physics and Chemistry, University of Palermo, Italy; 2CNR-IMM, Catania, Italy; 3Materials Science and Nanotechnologies PhD School, University of Catania and University of Palermo, Italy
Resume : Electronic applications of Graphene (Gr), the two dimensional carbon layer, pushes to clarify the potentialities of tuning the content and type of mobile species. Doping effects can be obtained on Gr grown by chemical vapor deposition (CVD) on metal (Cu, Ni, ) and transferred on specific substrates either during growth or by subsequent definite thermal treatments in controlled atmosphere. Many aspects of this latter procedure are still to be clarified as, for example, the role of Gr defective structures and planar morphology, or the Gr substrate features. The same thermal activated process is a matter of debate to try to clarify the nature of dopant-Gr physical bonding features. We report an experimental study by Raman and Atomic Force Microscopy of the thermal doping effects in the temperature range below 400°C on graphene grown by CVD on Cu and transferred on X/Si (where X = SiO2, Al2O3) substrates. The role of treatment atmosphere is shown highlighting a prominent role of oxygen in obtaining p-doping and vacuum in avoiding successive reactivity of entrapped species. By comparing different substrates the features of doping related to Gr and those connected to Gr substrate properties are clarified also by employing electrical characterization.
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