2014 Fall Meeting
Copper- and Zinc Oxide Based Materials for Sustainable Energy Technologies
Energy conversion technologies, especially photovoltaics, exhibit enormous growth aiming to extremely high power capacities per year. Therefore, nontoxicity and abundance of the materials in the earth are among the key requirements to energy conversion technologies. Some of the materials presently used in such technologies, like CdTe, III/Vs and CIGS (CuInGaSe2), may not be abundant enough for large scale use in energy conversion technologies involving conventional thin films. From this point of view, copper- and zinc based materials like ZnO, ZnS, Cu2O, CZTS, CuSCN are of special interest both in the form of thin films and nanostructures as active layers, electron and hole transporting layers or transparent contacts. This symposium will focus on recent advances in synthesis of copper- and zinc oxide-based materials and on their various functionalities for sustainable energy technologies.
Crystalline silicon is the dominant material used in energy conversion technologies, especially solar cells, but alternative materials are a key-factor of achieving long-term sustainable energy economic goals. Binary and ternary oxides and related materials are promising to reach these goals. For instance, combination of ZnO and Cu2O is shown as one of the promising approaches for the next generation photovoltaics. Theoretical predictions promise efficiencies of such solar cells up to 18%. Recently, a breakthrough has been reported demonstrating ZnO/Cu2O thin film solar cell with efficiency of ~5%. Nevertheless further investigations are needed in order to improve its efficiency. Alternatively, other combinations involving ZnO and compound semiconductors as absorbing layers in the form of thin films or nanostructures are also promising for the next generation photovoltaics. Materials issue is the key factor for improving efficiency of energy conversion technologies and reducing cost through the use of low-cost deposition techniques or of a small amount of materials via nanostructures for instance. The symposium will be focused on areas of growth technologies, advanced characterizations, novel device concepts and corresponding modeling. Progresses in the growth of thin films, heterostructures and nanostructures as well as new growth approaches will be discussed. Fabrication of oxides employing CVD, ALD, sputtering, deposition in solution will be discussed. A special attention will be given to the effects of the materials properties on the device efficiency, phenomena at interfaces, surface passivation, new precursors for CVD, ALD, deposition in solution and related growth mechanisms. Also, nanoparticles and nanowire arrays are considered as potential candidates for a variety of novel applications in different fields of energy conversion technologies and will be addressed. The use of oxides nanowires in axial and radial heterojunctions will be discussed.
The symposium will be an interdisciplinary event for scientists working in the field of oxides growth, characterization, and device fabrication. It should give an excellent opportunity to discuss the trends and challenges in the oxides-based sustainable energy technologies and to find partners for new breakthroughs in this area.
Hot topics to be covered by the symposium
- Novel device concepts for energy conversion
- Fabrication of thin films, heterostructures and nanotructures (i.e., nanowires, nanoparticles) by ALD, VPE, sputtering, pyrolisis, electro-deposition, hydrothermal methods
- Band gap engineering, strain engineering, surface passivation.
- Emerging technologies
- Characterization, advanced analytical tools
- Oxides for photovoltaics
- Heterojunctions involving oxides nanostructures (nanoparticles, nanowires)
- Investigation of the buffer layer / absorber interface phenomena
- Materials for transparent contacts
List of invited speakers
- Reinhard Carius, Institute of Energy and Climate Research, Jülich, Germany
- NEXCIS Photovoltaic Technology, France
- Bartlomiej Witkowski, Institute of Physics, Warsaw, Poland
- Tomasz Stapinski, AGH University of Science and Technology, Poland
- Atsushi Suzuki, University of Shiga Prefecture, Japan
- Meng Tao, Dept. of Electr. Eng., University of Texas at Arlington, Arlington, USA
- Ming Li, College of Physics and Information Technology, Shaanxi Normal University, Xi’an, China
- H. Brückl, Austrian Institute of Technology, Vienna, Austria
- Kwang-Leong Choy, Faculty of Engineering, Energy and Sustainability Research Division, University of Nottingham, United Kingdom
- W. Walukiewicz, Solar Energy Materials Research Group, Laurence Berkeley National Laboratory, USA
- C. Lévy-Clément, Institut de Chimie et des Matériaux, Paris, France
- Thierry Pauporté, Chimie Paris Tech, Paris, France
- Steve Dunn, Queen Mary University of London, London, United Kingdom
List of scientific committee members
- Marius Grundmann, Leipzig University, Germany
- Ewa Placzek-Popko, Wroclaw Technical University, Poland
- Alexander Efros, Naval Research Laboratory, Washington, USA
- Daniel Lincot, IRDEP, Paris, France
- Carsten Ronning, Jena University, Germany
- De-Zhen Shen, Changchun Inst Opt Fine Mech & Phys, China
The symposium will be co-organized by the EU 7th Framework Programme under the project REGPOT-CT-2013-316014 (EAgLE)
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Authors : M. Welna1, 2, R. Kudrawiec1, Y. Nabetani3, J. Misiewicz1, and W. Walukiewicz2
Affiliations : 1 Institute of Physics, Wrocław University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 Department of Electrical Engineering, University of Yamanashi, Takeda 4-3-11, Kofu 400-8511, Japan
Resume : Group II-VI alloys such as ZnSeO or ZnTeO are a new class of semiconductors called highly mismatched alloys (HMAs). In these materials group VI atoms are partially replaced with oxygen. The incorporation of small amount of oxygen atoms in ZnSe lattice leads to formation of an intermediate band (E-) located below the conduction band edge (E+). This splitting into two subbands is well explained by the band anticrossing model [1-2]. Dilute group II-VI oxide alloys (e.g. ZnSeO) have recently attracted attention as promising materials for intermediate band solar cells (IBSC). Realization of the IBSC concept will require a better understanding of the properties of ZnSeO alloys. We have used photoreflectance (PR) and photoluminescence (PL) to study temperature dependence of the band gap of ZnSe1-xOx with oxygen concentration up to 1.35%. A rapid decrease of the temperature induced band gap shift (ΔEg) have been observed for oxygen concentrations above 0.8%. The results are explained by the anticrossing interaction between extended conduction band states of ZnSe host and weakly temperature dependent localized states of substitutional O atoms.
Authors : M.A. Pietrzyk, M. Stachowicz, D. Jarosz, E. Przezdziecka, A. Reszka, J.M. Sajkowski, A. Kozanecki
Affiliations : Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46 02-668, Warsaw, Poland
Resume : One dimensional ZnMgO/ZnO nanostructures have great potential for applications in the fields of optoelectronic and sensor devices. Ternary ZnMgO alloys present a suitable material system which allows widening of the band-gap up to 3.9 eV for x = 0.33 before any structural phase transition to cubic ZnMgO occurs. Using this alloy system the exciton binding energy can be increased in ZnMgO/ZnO/ZnMgO quantum well structures from 60 meV in bulk ZnO up to ~100 meV in quantum wells. We report on the growth conditions, structural and optical properties of ZnO/ZnMgO multiple quantum wells (MQWs) in nanocolumns ZnMgO grown on Si (111) substrates by MBE without employing a catalyst. Ten periods of ZnO/ZnMgO MQWs (wells widths of 1.7 and 3 nm, barriers 2 and 15 nm) were sandwiched between thick ZnMgO cap and buffer layers or substrate. When the distance between the two QWs is small enough, the wave functions of charge carriers overlap and tunneling is possible through the barrier. The problem of finding the treshold thickness for this barrier, predicted by theoretical calculations, still has not been confirmed experimentally. Scanning electron microscopy shows that ZnMgO nanorods with various density and diameter could be controlled by growth temperature of nanocolumns and the temperature of buffer layers grown. On the photoluminescence (PL) spectra we observed a blue shift of excitonic emission in comparison with bulk ZnO values which demonstrates quantum confinement in the ZnO wells with thicknesses smaller than 4 nm. We also demonstrate that excitonic emission from QWs is dominated by excitons bound to donors. The characteristic energy of PL decay of the dominant excitonic lines agrees well with the values of localization energies of excitons to donor centers. The cathodoluminescence mapping performed on a cross section of the sample show that emission at 3.342 eV comes from the ZnO QW`s and emission from 3.73 eV comes from the ZnMgO buffer layer. The XRD spectra suggest that ZnMgO films grow with the c-axis preferred orientation. The work was supported by the European Union within the European Regional Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-008/08). One author (M.A.P.) would like to acknowledge the support by the NCN project DEC-2013/09/D/ST5/03881.
Session II : -
Authors : Ramon Schifano1, Tomasz A. Krajewski1, Dmytro Snigurenko1, Grzegorz Luka1, Elzbieta Guziewicz1, Krzysztof Kopalko1, Krzysztof Goscinski1, Marek Godlewski1, 2
Affiliations : 1 Institute of Physics, Polish Acad. of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland; 2 Dept. of Mathematics and Natural Sciences College of Science Cardinal S. Wyszynski University, ul. Dewajtis 5, 01-815 Warsaw, Poland
Resume : ZnO has recently attracted a lot of interest as a potential semiconducting partner for modern electronics, either as a TCO material or as an active part of the device. This work presents a study of the annealing effects on the electrical characteristics and morphology of epitaxial ALD ZnO films (Al and unintentionally doped ones). The preliminary studies show that Al doped ZnO layers (AZO) obtained at 300°C exhibit stable electrical properties (electron concentration about 10^19-10^20 cm^-3) after Rapid Thermal Annealing (RTP) in oxygen up to 500°C. On the other hand, the resistivity of unintentionally doped ZnO can be tuned within 3 orders of magnitude (from 0.01 to 10 Ohm*cm) in similar RTP process also affecting the films morphology. This paves the way to the realization of AZO/ZnO/metal structures with a carrier concentration in the ZnO layer suitable for the Schottky diodes construction. A comparison with the ZnO-based junctions using low resistive Si as a back contact and exhibiting a rectification ratio up to 106 at +/-2V (with series resistance from 200 to 400 Ohm) is shown. The research was supported by the EU through the Innovative Economy grant POIG.01.01.02-00-008/08. The authors T.A.K., K.K. and K.G. acknowledge support by the grant DEC 2013/09/D/ST5/03879 of NSC of Poland. The authors E.G. and D.S. were supported by Polish NCBiR project DZP/PBSII/1699/2013. The author R.S. was supported by the EU 7th Framework Programme project REGPOT-CT-2013-316014 (EAgLE)
Authors : 1K. Marszałek, 1T. Stapiński, 2R. Pietruszka, 2S. Gierałtowska, 2Ł. Wachnicki, 2B.S. Witkowski, 2M. Godlewski
Affiliations : 1AGH University of Science and Technology,al. Mickiewicza 30, 30-059 Krakow, Poland 2Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668, Warsaw Poland
Resume : Properties of glass with antireflection layer/TCO substrates were optimized for photovoltaic applications. Antireflection layer was coated on the surface of low-iron glass. The reason of choosing low-iron type glass was its higher transmittance, especially in the close infrared range when compared to standard float glass. Superior optical parameters could be achieved due to low content of iron oxides. Especially ferrous oxide FeO shows absorption band in close infra-red and it overlaps the band of PV's semiconductors. For this reason the ratio of ferrous oxide to ferric oxide should be kept at as low limit as possible. Glass sample was treated in chemicals in order to remove alkali ions. Selective leaching of alkali from the surface region leaves a thin layer reach in silica. Due to porous structure its refractive index is close to the desired value, which is geometric mean of refractive indexes of glass and air. Conventional multilayers with alternating high and low refractive indices are very effective in the visible region but cannot be used for the solar spectrum because their effect is to increase reflection at double the design wavelength. For this reason monolayers of low refractive index are commonly used. Glass leaching is a very convenient way of preparing an anti-reflection layer because etched layer does not delaminate from the glass surface. Moreover this approach allows for precise control of the thickness of a thin low-reflection film. The so-prepared glass with the anti-reflection layer was used as a substrate for deposition with either ZnO or Aluminum doped ZnO (AZO), which form a transparent conductive oxide (TCO) films. ZnO and then AZO layers were deposited at low temperature using organic zinc precursors (mostly diethyl zinc), water vapors as oxygen precursor and Atomic Layer Deposition (ALD) method. After optimization of the ALD growth procedure, layers with a high transparency (between 80 and 90%) and good electrical properties were obtained. Their morphology, stoichiometry and structural properties were investigated with AFM, XRD, EDX and SEM methods. Based on these studies and electrical and optical investigations we confirm their applicability for applications in a new generation of photovoltaic systems. The paper was financially supported by European Union from the sources of the European Regional Development Fund for 2007-2013, the Innovative Economy Operational Programme Priority Axis 1 Research and development of state-of-the-art. technologies POIG.01.03.01-30-056/12 and DEC-2012/06/A/ST7/00398 (IFPAN).
Session III : -
Authors : Thierry Pauporte
Affiliations : Institut de Recherche de ChimieParis, CNRS-Chimie ParisTech, UMR8247, 11 rue Pierre et Marie Curie, 75005 Paris, France.
Resume : Electrochemical deposition techniques are highly relevant for the preparation of oxide layers with precisely controlled morphological, structural, optical and electrical properties. The advantages of the techniques include the deposition at low temperature of high quality material, the precise control of the (nano)structure morphology and thickness, the control of the electrical properties and the excellent electrical contact between the deposited layers and the substrate. By playing on the deposition parameters, we have prepared tailored ZnO films such as nanowires/nanorods arrays, dense 2-D layers, as well as mesoporous films and hierarchical structures. We will also describe the integration of these films in efficient solution-processed photovoltaic devices. Electrodeposited layers have been optimized for photoelectrode application in dye-sensitized solar cells (DSSCs) and in perovskite solar cells (P-SC). We will also show that nanostructured electrodeposited ZnO can be combined with electrodeposited Cu2O for the preparation of nanostructured p/n junction solar cells.
Authors : R. Pietruszka1, G. Luka1, B. S. Witkowski1, L. Wachnicki1, S. Gieraltowska1, R. Schifano1, E. Zielony2, P. Bieganski2, E. Płaczek-Popko2, M. Godlewski1,3
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 2Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland; 3 Department of Mathematics and Natural Sciences College of Science, Cardinal Stefan Wyszynski University, Warsaw, Poland
Resume : Zinc oxide (ZnO), a wide band gap semiconductor (3.3 eV at room temperature), and zinc oxide doped with aluminum (ZnO:Al) are intensively studied for photovoltaic applications. First, n-type conductivity makes ZnO promising material as n-type partner for p-type silicon or p-type cadmium zinc telluride and cadmium telluride. Moreover, zinc oxide doped with aluminum can be used as a TCO material. In the present work we test above mentioned ZnO application for ZnO films grown by Atomic Layer Deposition (ALD). In the first approach, we grew thin films of n-type ZnO on p-type crystalline substrates. Such obtained PV structures of the 2nd generation show efficiency of about 6%. In addition to ZnO films, we also investigated ZnO nanorods for photovoltaic applications. The nanorods were grown by a hydrothermal method at temperature of 50°C. We were able to regulate orientation and sizes of the ZnO nanorods in a large extent. The best PV efficiency for such 4th generation structures (ZnO:Al/ZnO/ZnONR/Si/Al) was equal to 12.5%. This work was partially supported by the Innovative Economy grant (POIG.01.01.02-00-008/08), the National Centre for Research and Development grant (PBS1/A5/27/2012), and (E. Zielony, P. Biegański and E. Placzek-Popko) by the National Laboratory of Quantum Technologies (POIG. 02.02.00-00-003/08-00).
Authors : Nimra Jalali, Joe Briscoe, Yan Zhi Tan, Peter Woolliams, Mark Stewart, Paul M. Weaver, Markys Cain, Steve Dunn
Affiliations : Queen Mary University of London, UK; Nan Yang Polytechnic, Singapore; National Physical Laboratory, UK
Resume : We report the method to passivate ZnO nanorods using: (1) CuSCN (Copper thiocyanate) and (2) PDDA (Poly(diallyldimethylammonium chloride)) and PSS (sodium 4-styrenesulfonate)) in ZnO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) energy harvesters. Previous studies have focused on improving the performance of schottky junction and insulator-type devices. However, this work focuses on the impact of ZnO nanorods passivation in p-n junction device and analyses its impedance measurement and time constant. The polyelectrolytes and CuSCN passivation resulted in 897 mV and 470 mV output which were 4 and 7 times higher the non-passivated device. The peak power density also increased from 44 µW/cm2 to 120 µW/cm2 and 318 µW/cm2 with polyelectrolytes and CuSCN passivation. The interaction between metal oxide and polyelectrolytes is physisorption rather than chemisorption which is in case of CuSCN. Due to strong bonding between CuSCN and ZnO, it resulted in higher output than with the polyelectrolytes. The impedance results explain relationship between time constants and passivation. The time constant increases from 0.0045 ms for non-passivated to 1.14 ms for passivated ZnO, which indicates improved charge storage in ZnO and decrease in the internal screening rate. Hence, it is confirmed that, surface passivation of nanorods reduces the screening rate and improves the nanogenerator performance.
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Authors : Fengyan Zhang, Xin Cui, Wenzhi Chen, Xuan Huang, Ran Zhang, Chuwei Zhong,Qijin Cheng, Daqin Yun
Affiliations : College of Energy, Xiamen Univeristy, Xiamen, China
Resume : This paper will discuss our research approaches for printable CZTS/CIGS thin film solar cell, which will include CZTS/CIGS nanoparticle syntheses using thermal injection method; forming high quality CZTS/CIGS layer by solution based method and annealing; Using MoNa electrode or Na ion solution process to further improve the crystalline of the CZTS/CIGS layer ; forming printable Mo back contact using Mo ink; and using solution method to form AZO nanorod sandwich layer to improve light absorption. We have observed significant improvement on the efficiency of CZTS/CIGS solar cell by optimizing MoNa back contact, using Na ion solution, by special ambient annealing process and using AZO nanorod sandwich layer as the window layer. Detail will be addressed at the presentation.
Authors : J.E. ten Elshof
Affiliations : University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands
Resume : Electrodeposition is an established method for the controlled deposition of metals and metal oxides. By carrying out electrodeposition inside a template, well-defined and complex architectures with micrometer and submicrometer dimensions can be made. The method can also be extended to combine different materials, so that composite architectures consisting of metal and metal oxide segments, or different oxide segments can be realized. In this contribution the application of templated electrodeposition to form semiconducting nanowires, nanotubes and nanocubes of various compositions is demonstrated. The first example are composite nanowires with photocatalytic property. Axially segmented ZnO|Ag and ZnO|Au nanowires were made by sequential deposition from different precursor solutions. Ag@TiO2 nanowires with core-shell morphology was obtained via a 2-step electrodeposition strategy that involved the formation of a hollow metal oxide nanotube, followed by filling them with Ag. The as-formed wires had a length of 3-6 micrometer, wire diameters of 50-300 nm, and were found to be active in the photocatalytic conversion of water. The second example are p-Cu2O nanocubes and Ni|p-Cu2O nanobars. Photocurrent measurements of 200-500 nm p‐Cu2O nanocubes indicated that they show a higher activity at 0 V vs. NHE, an increased photocurrent at more positive potentials, e.g. 0.3 V vs. NHE, and a higher dark current than comparable p-Cu2O films.
Authors : Joo-Hyun Park, Bo Keun Park, Taek-Mo Chung, Chang Gyoun Kim*
Affiliations : Korea Research Institute of Chemical Technology
Resume : We have prepared molecular precursors of Cu, Zn and Sn. The precursors contain a metal and sulfur together in a molecule, respectively. The precursors have been characterized by spectroscopic analyses, EA and X-ray single crystallography. Solvothermal decomposition of stoichiometric combination of Cu, Zn, Sn precursors produced crystalline CZTS nanoparticles.
Authors : E Przeździecka, M. Stachowicz, D. Dobosz, R. Jakieła, K. Kopalko, A. Wierzbicka, A. Kozanecki
Affiliations : Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Resume : Zinc oxide is a prospective material for a number of applications such as ultraviolet light emitters or detectors. In this work we study the high quality p-ZnO/n-GaN heterostructures consisting of nitrogen doped ZnO:N films grown by MBE, and n-type GaN templates. The quality of the heterojunction was examined by X-ray diffraction, atomic force and scanning microscopy (AFM, SEM) and PL measurements. The nitrogen concentration, as measured by SIMS, is ~1x1020 cm-3. Incorporation of nitrogen atoms in the ZnO lattice was confirmed by the analysis of photoluminescence spectra which allowed to assign the PL peaks at 3.362 eV and 3.316 eV to N-acceptor. Room temperature Hall measurements in the van der Pauw configurations revealed p-type conductivity of ZnO:N layers with the hole concentration ~1016 cm-3 and Hall mobility 20 cm2/Vs. The maximum forward-to-reverse current ratio IF/IR in the obtained p-n diodes is of the order of about 107 at the bias of ±5 V. This is a very good result for this type of heterojunction. The difference between black and UV light current in the reverse voltage is at about four orders of magnitude. The observed wavelength dependence of the photocurrent confirmed the high selectivity of the photodiodes. One author (E.P) would like to acknowledge the support by the NCN project DEC-2013/09/D/ST3/03750. The work was supported by the European Union within the European Regional Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-008/08).
Authors : Mongia.Hosni, Thierry Pauport?, Samir Farhat, Nouredine Jouini
Affiliations : Institut de Recherche de ChimieParis, CNRS-Chimie ParisTech, UMR8247, 11 rue Pierre et Marie Curie, 75005 Paris, France; Laboratoire des Sciences des Proc?d?s et des Mat?riaux, LSPM UPR 3407, Universit? Paris 13/ CNRS, Sorbonne Paris Cite, 93430 Villetaneuse, France.
Resume : The forced hydrolysis in polyol medium is a versatile synthesis method for the preparation of metal oxide particles with controlled properties. We investigate the D149-organic dye and the TG6 Ru-dye-sensitized solar cell (DSSC) performances of ZnO film electrodes prepared with four different types of nanoparticles having various size and morphology and prepared using this method for most of them. The photoanode dye loading has been determined and the cells have been studied by impedance spectroscopy (IS) at various applied voltages. From the analysis of the IS spectra the key functioning parameters of the various photoelectrodes such as trap state distribution, electron transfer time and electron lifetime have been determined. The particle shape and size deeply influence the dye loading and the electronic structures of the trap state levels localized below the conduction band edge. Low open circuit voltage and fill factor are found in the case of small (8nm) spherical particles because of very deep energy states related to large particle necking and high density of grain boundaries. On the other hand, layers made of sintered large hexagonal rod-like particles (35 nm in diameter) of high crystalline quality show satisfying dye loading, shallower energy trap states, higher conductivity and very high charge collection efficiency.  M. Hosni, Y. Kusumawati, S. Farhat, N. Jouini, Th. Pauport?, Effects of Oxide Nanoparticle Size and Shape on Electronic Structure, Charge Transport and Recombination in Dye-Sensitized Solar Cell Photoelectrodes, J. Phys. Chem. C, (2014) DOI: 10.1021/jp412772b.
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 : A usage of energy upconversion layers leads to increase of an overall efficiency of the Si-based solar cells and potentially can push their Shockley-Queisser efficiency limit up to 40 %. Er2O3 containing ceramics are promising candidates for the upconversion layers which absorb energy in the near infrared range and reemitting it in the visible range. Photons with the higher energy can then be successfully utilized in the Si p-n junction. Wide-band gap semiconductor ZnO has an average transmittance coefficient higher than at least 80 % in the visible and near infrared ranges and thus presents a good host material for Er2O3 clusters. In this work we studied a cathodic electrochemical deposition of the mixed ZnO and Er2O3 layers on the Si substrates from the nitrate bath under different conditions. It was shown that depending on a current density the ZnO/Er2O3 layers of different morphologies ranging from continuous films to arrays of nanostructures can be formed. A concentration level of Er2O3 varied from 1 to 7 at. %. Photoluminescence, up-conversion photoluminescence as well as reflection spectra of the deposited layers were studied. It was revealed that the layers with more developed morphology consisting of ZnO/Er2O3 nanocrystals and nanosheets are less reflective and have greater prospects as the upconversion layers for the Si-based solar cells with the enhanced efficiency. The work has been supported by the Belarus Government Research Program Electronics, grant 1.2.08.
Authors : A.I. Savchuk1, I. Stefanuik2, I.D. Stolyarchuk1, G.I.Kleto1, A. Dziedzic2, I. Rogalska2, E. Sheregii2
Affiliations : 1Department of Physics of Semiconductors and Nanostructures, Chernivtsi National University, 2 Kotsyubynsky Street, 58012 Chernivtsi, Ukraine;2 Centre for Innovation and Transfer of Natural Sciences and Engineering Knowledge, University of Rzeszow, 16a Rejtana Street, 35959 Rzeszow, Poland
Resume : Zinc oxide (ZnO) is a multifunctional inorganic semiconductor material with industrial applications in many fields. Doping in ZnO transition metal elements offers an effective method to adjust its electrical, optical, and magnetic properties, which is crucial for its practical applications. The present work is devoted to preparing of ZnCoO thin films and study of their structural and magnetic properties depending on content of cobalt. Zn1-xCoxO thin films were deposited onto glass and quartz substrates by RF-plasma sputtering technique. Content of cobalt in the deposited films has varied in range of 0
Authors : R. Parize,1,2 J. Garnier,1,2 S. Guillemin,1,2,3 E. Appert,1,2 V. Consonni.1,2*
Affiliations : 1) Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France 2) CNRS, LMGP, F-38000 Grenoble, France. 3) Institut des Nanotechnologies de Lyon, Université de Lyon, UMR 5270 CNRS - INSA Lyon, 7 avenue Jean Capelle 69621 Villeurbanne, France.
Resume : ZnO nanowires (NWs) grown by chemical bath deposition (CBD) have received over the last decade increasing interest for a large number of electronic, optoelectronic and photovoltaic devices. However, a critical point for using ZnO NWs in these devices is still the precise control of their structural morphology. The structural properties of ZnO NWs basically depend on the structural morphology of the ZnO seed layer consisting of ZnO nanoparticles (NPs) [1,2] as well as on the growth conditions used in CBD (i.e., chemical precursors, temperature). It is found that the growth of ZnO NWs is limited by the mass transport of chemical precursors in solution . Also, ZnO NWs homoepitaxially nucleate on the free surface of ZnO NPs with polar c-plane orientations . A special emphasis is made on the effects of several types of chemical precursors (i.e., zinc nitrate, hexamethylenetetramine, ammonia, and polyethylenimine) on the structural properties of ZnO NWs such as their density, diameter, length and vertical alignment. This leads to a better understanding of the growth mechanisms of ZnO NWs by CBD, which can enable for instance the formation of ZnO NWs with aspect ratio as high as 50 while maintaining diameters smaller than 100 nm.  S. Guillemin V. Consonni, E. Appert, E. Puyoo, L. Rapenne, H. Roussel, J. Phys. Chem. C 116, 25106 (2012).  S. Guillemin, L. Rapenne, H. Roussel, E. Sarigiannidou, G. Brémond, V. Consonni, J. Phys. Chem. C 117, 20738 (2013).
Authors : S.R. Tankio Djiokap; Z.N. Urgessa; C. Mbulanga; J.R. Botha
Affiliations : Nelson Mandela Metropolitan University
Resume : A two-step chemical bath deposition process has been used to synthetise ZnO nanorods on Si (100), (111), moderately doped (p) and heavily doped (p+). The two-step chemical bath deposition used here to grow ZnO nanorods involves the formation of a seed layer of ZnO nanoparticles as a first step (using zinc acetate and ethanol), followed by the growth of ZnO nanorods from solution (using a mixture of aqueous solutions of zinc nitrate hexahydrate and hexamine). The scanning electron microscopic and the x-ray diffraction reveal that the orientation of the silicon does not affect the structural and morphological properties of ZnO nanorods. Current-voltage (I-V) measurements reveal that the electrical behaviour of the heterojunction depends on the dopant density of the silicon. Although post growth annealing improves the photoluminescent properties, the best electrical properties (I-V) are obtained for the as-grown sample. Indeed, the I-V characteristics of the sample grown on p+ substrate clearly show ohmic behaviour. In contrast the sample grown on (p) substrate is rectifying. Rectification ratios (± 3 V) of ~ 280 and ~30 were measured for the as-grown and annealed (300°C) samples, respectively, indicating that annealing negatively affected the electrical properties of the junction.
Authors : E Przeździecka, M. Stachowicz, D. Dobosz, R. Jakieła, K. Kopalko, A. Wierzbicka, A. Kozanecki
Affiliations : Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Resume : Zinc oxide is a prospective material for a number of applications such as ultraviolet light emitters or detectors. In this work we study the high quality p-ZnO/n-GaN heterostructures consisting of nitrogen doped ZnO:N films grown by MBE, and n-type GaN templates. The quality of the heterojunction was examined by X-ray diffraction, atomic force and scanning microscopy (AFM, SEM) and PL measurements. The nitrogen concentration, as measured by SIMS, is ~1E20 cm-3. Incorporation of nitrogen atoms in the ZnO lattice was confirmed by the analysis of photoluminescence spectra which allowed to assign the PL peaks at 3.362 eV and 3.316 eV to N-acceptor. Room temperature Hall measurements in the van der Pauw configurations revealed p-type conductivity of ZnO:N layers with the hole concentration ~1E16 cm-3 and Hall mobility 20 cm2/Vs. The maximum forward-to-reverse current ratio IF/IR in the obtained p-n diodes is of the order of about 1E7 at the bias of ±5 V. This is a very good result for this type of heterojunction. The difference between black and UV light current in the reverse voltage is at about four orders of magnitude. The observed wavelength dependence of the photocurrent confirmed the high selectivity of the photodiodes. One author (E.P) would like to acknowledge the support by the NCN project DEC-2013/09/D/ST3/03750. The work was supported by the European Union within the European Regional Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-008/08)
Authors : L. Khomenkova, V.I. Kushnirenko, N.M. Osipyonok, A.F. Singaevsky, G.S. Pekar, K.A. Avramenko, V.V. Strelchuk, Yu.O. Polishchuk, V.P. Kladko, L.V. Borkovska
Affiliations : V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauky 41, 03028 Kyiv, Ukraine
Resume : Photoluminescence (PL) and Raman scattering spectra as well as XRD patterns of undoped and Li-doped ZnO films produced by a simple and low-cost screen printing method on Al2O3 substrates were studied. The films were sintered at T=800, 900 and 1000°C for t=30-180 min in the air. Undoped ZnO films demonstrated a pronounced increase in the intensity of the excitonic PL band when either T increased from 800 up to 1000°C for the films sintered for t=30 min or when sintering time arose from 30 to 60 min for specified T. The evolution of the PL spectra was accompanied by the decrease in the intensity of the A1LO peak at about 584 cm-1 in the Raman scattering spectra and was ascribed to the improvement of films crystalline quality. The doping with Li from LiNO3 allowed the films of higher crystalline quality to be obtained even at T=800°C and t=30 min because of flux ability of Li ions. The effect of sintering conditions on the parameters of defect-related PL bands observed in the green-orange (500-600 nm) and red (700-720 nm) spectral range was also investigated. In Li-doped ZnO films, an enhancement of orange PL band peaked at about 580 nm was found. The interdiffusion processes occurring at ZnO/Al2O3 interface in the Li-doped ZnO films and resulting in specific transformations in the PL and PL excitation spectra of defect-related band are discussed.
Authors : M.I. Lukasiewicz, E. Guziewicz*, B.S. Witkowski, L. Wachnicki, M. Godlewski
Affiliations : Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Resume : Zinc oxide doped with transition metals (Cu, Mn, Co ) has been continually focusing a lot of attention because of possible applications in spintronics. According to the theoretical predictions magnetic and electrical properties of these materials are closely related and the p-type conductivity is required for ferromagnetic behavior. However, the latter one is extremely difficult to obtain in ZnO mainly because of strong compensation effects. We present the results of synchrotron radiation photoemission and electrical measurements taken on Zn(Cu)O films grown by Atomic Layer Deposition (ALD) at temperature 250 and 300oC using diethylzinc as a zinc precursor, copper acethyloacetonate as a copper precursor and deionized water as an oxygen precursor. The copper concentration in the films varies between 3 and 50% and depends on the relation between the zinc precursor versus the copper precursor doses in the ALD growth process. Hall measurements show that the type of conductivity is not related to the copper content, but strongly depends on growth temperature. The Zn(Cu)O samples grown at 300oC show a high n-type conductivity, whereas these grown at 250oC are highly resistive or p-type. Moreover, n-type and p-type films reveal completely different electronic structure even if copper content in both types of films is very similar. The work was supported by the NSC of Poland (project no. DEC-2013/09/N/ST5/00896) and by EC FP7 programme (FP7/2007-2013) under agreement no. 226716.
Authors : M.I. Łukasiewicz1, B.S. Witkowski1, A. Wittlin1,2, M. Jaworski1, K. Kopalko1, M. Godlewski1,2
Affiliations : 1 Institute of Physics PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 2 Dept. Mathematics and Natural Sciences, College of Sciences UKSW, Dewajtis 5, 01-815 Warsaw, Poland
Resume : ZnO is a very interesting material for range of applications in microelectronic, optoelectronic and photovoltaic devices. For example, it can be used as a transparent conductive oxide (TCO) film in blue light emitters, in UV light sensors and in solar cells . In addition, ZnO doped with transition metal (TM Co, Cu, Mn, ) ions is intensively studied for spintronics applications . So the research on high-quality (Zn,TM)O alloy systems is becoming fairly important. Several reports suggest the important role of intrinsic defects [3-6] which may be of nm sizes and thus difficult to detect. AC microwave conductivity measurements are very sensitive to the small size metallic TM inclusions of metal with a high conductivity, which in the DC conductivity are not visible. Therefore, AC measurements allow us to investigate uniformity of TM-distribution in (Zn,TM)O films. In the present paper we demonstrate direct correlation between sample uniformity, Mn (Co, Cu, ) concentration, growth parameters and AC conductivity of our films. The project was financed by the National Science Centre granted based on the number of decision DEC-2013/09/N/ST5/00896.  U. Ozgur, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, and H. Morkoc, J. Appl. Phys. 98, 041301(2005).  K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 40, L334 (2001).  X. Zhang et al., Phys. Rev. B 80, 174427 (2009).  J.M.D. Coey et al., J. Phys. D: Appl. Phys. 41, 134012 (2008).  A. J. Behan et al., Phys. Rev. Lett. 100, 047206 (2008).  M. Godlewski et al., Phys. Status Solidi (b) 248, 1596 (2011).
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Authors : J. Michallon,1,2,3,4 J. Garnier,1,2 S. Renet,5 D. Bucci,3,4 L. Rapenne,1,2 Q. Rafhay,3,4 L. Artus,6 E. Appert,1,2 A. Kaminski-Cachopo,3,4 V. Consonni,1,2
Affiliations : 1) Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France 2) CNRS, LMGP, F-38000 Grenoble, France 3) Univ. Grenoble Alpes, IMEP-LAHC, F-38000 Grenoble, France 4) CNRS, IMEP-LAHC, F-38000 Grenoble, France 5) CEA, LETI, Minatec Campus, F-38054 Grenoble, France 6) Institut Jaume Almera, Barcelona, Spain
Resume : ZnO nanowire (NWs) based extremely thin absorber (ETA) solar cells are promising photovoltaic (PV) structures to decrease material consumption while maintaining high power conversion efficiency. The conversion efficiency of 4.74 % has for instance been reported in ZnO/CdSe core shell NW-based solar cells . An alternative route consists in combining ZnO with CdTe, for which the conversion efficiency of 12.3% has recently been achieved in planar layers . The aim of this study is to analyze and optimize the PV performances of ZnO/CdTe core shell NW-based solar cells and to elucidate the issues limiting the conversion efficiency. For this purpose, rigorous coupled wave analysis simulations are performed using a home-made software to improve the absorption properties of ZnO/CdTe core shell NW-based ETA solar cells by optimizing their structural dimensions. The physical origins of light trapping are investigated by systematic optical computations of the ideal short-circuit current density and by optical mode analysis. The low-cost fabrication of ZnO / CdTe core shell NW arrays is further shown by combining chemical bath deposition with close space sublimation and annealing effects in chlorine compound atmosphere are revealed on their physical properties .  J. Xu et al., Nano Lett. 11, 4138 (2011).  M.G. Panthani et al., Nano Lett. 14, 670 (2014).  V. Consonni et al., Nanoscale Res. Lett. 9, 222 (2014).
Authors : Joe Briscoe, Sabina M. Hatch and Steve Dunn
Affiliations : Joe Briscoe, Steve Dunn: Queen Mary University of London, UK; Sabina M. Hatch: University College London, UK
Resume : We present a method to produce a ZnO nanorod/CuSCN diode by spray deposition of CuSCN into solution grown ZnO nanorods, which leads to excellent infiltration of the ZnO nanorods and a uniform film. This method leads to improved diode properties compared to alternative methods, and this enables the use of the heterostructure as a self-powered UV photodetector with excellent properties. UV photodetectors typically require an external bias, but for self-sufficient sensors systems self-powered functionality is essential. At a nominal zero-applied field, the device produces a photocurrent response of 4.5 µA for a low UV (375 nm) irradiance of 6.0 mW/cm2. A fast 500 ns rise and 6.7 µs decay time was recorded with a UV/visible rejection ratio of ~100. With a small applied bias of +0.1 mV a rapid detection time of 4 ns was possible. For comparison to similar heterostructures a responsivity of 9.5 AW-1 was measured at -5 V applied bias. The photodetector performance was attributed to the superior diode properties achieved using this method, enabling the use of the UV-excited photovoltaic behaviour for self-powered photodetection. Therefore the ZnO/CuSCN UV photodetector is suitable for nanoscale applications that require rapid response times and self-sufficiency. In addition, this method is applicable to a number of systems where the p-type properties of CuSCN can be utilised, including photovoltaic devices where such improved diode behaviour could translate to enhanced efficiency.
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