Copper- and Zinc Oxide Based Materials for Sustainable Energy Technologies

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.

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.

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.

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).

Resume : The forced hydrolysis in polyol medium is a versatile synthesis method for the preparation of metal oxide particles with controlled properties.[1] 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. [1] 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.

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.

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

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 [1]. Also, ZnO NWs homoepitaxially nucleate on the free surface of ZnO NPs with polar c-plane orientations [2]. 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. [1] S. Guillemin V. Consonni, E. Appert, E. Puyoo, L. Rapenne, H. Roussel, J. Phys. Chem. C 116, 25106 (2012). [2] S. Guillemin, L. Rapenne, H. Roussel, E. Sarigiannidou, G. Brémond, V. Consonni, J. Phys. Chem. C 117, 20738 (2013).

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.

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)

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.

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.

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 [1]. In addition, ZnO doped with transition metal (TM – Co, Cu, Mn,…) ions is intensively studied for spintronics applications [2]. 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. [1] 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). [2] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 40, L334 (2001). [3] X. Zhang et al., Phys. Rev. B 80, 174427 (2009). [4] J.M.D. Coey et al., J. Phys. D: Appl. Phys. 41, 134012 (2008). [5] A. J. Behan et al., Phys. Rev. Lett. 100, 047206 (2008). [6] M. Godlewski et al., Phys. Status Solidi (b) 248, 1596 (2011).

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 [1]. An alternative route consists in combining ZnO with CdTe, for which the conversion efficiency of 12.3% has recently been achieved in planar layers [2]. 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 [3]. [1] J. Xu et al., Nano Lett. 11, 4138 (2011). [2] M.G. Panthani et al., Nano Lett. 14, 670 (2014). [3] V. Consonni et al., Nanoscale Res. Lett. 9, 222 (2014).

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.