Preparation Of Cuin（Se,S）₂, CuZnSnS₄Thin Films By Electrodeposition Technique And Their Structural Properties

Currently, CuInxGa1-xSe2(CIGS) has been regarded as one of the most promising light absorbingmaterials for thin film solar cells. Its conversion efficiency is comparable with that of monocrystallinesilicon. On the other hand, its features of thin films are advantageous than the monocrystalline silicon forthe fabrication of low-cost and high-quality thin film solar cells. To date, CIGS solar cells havedemonstrated the highest photoelectric conversion efficieny exceeding20%at labroatory scale. A team atSwitzerland’s Empa’s Laboratory for Thin Film and Photovoltaics has achieved a new record value forflexible CIGS solar cells of18.7%in2011, which indicated its wide application for fleible substrates in thefuture. CIGS based thin film solar cells are considered as the best and the most practical system with highefficiency and low-cost.CIGS thin films can be produced by various approaches, such as three steps of evaporation, magnetronsputtering/selenization, and electrodeposition technique. The vacuum-based techniques, such as co-evaporation and sputtering, are neither particularly low-cost nor versatile for the large-scale production dueto the low growth rates, and relatively high energies and controlled atmosphere it requires. Conversely,electrodeposition technique is seen as promising alternative tool to obtain low-cost CZTS precursor films,as it offers a number of combined advantages to lower the manufacturing costs: high materials utilization,reduced machine investments, faster coating capabilities over large areas, and compatibility with roll-to-rollprocesses for high throughput production. Unfortunately, the conversion efficiecy of electrodepositionbased CIGS thin film solar cells is lower than that of vacuum based one. Therefore further efforts areneeeded to fabricate the high quality CIGS thin films through the parameters optimization during theelectrodeposition. On the other hand, CIGS consist of rare elements, such as indium (In), and gallium (Ga).The materials scarcity could limit the CIGS production and its practical applications. Fortunately, kesteritecopper zinc tin chalcogenide (CZTS) has emerged as an earth-abundant and environment friendlier versionof CIGS where indium and gallium are substituted by tin and zinc respectively. The device architecturesand growth techniques can be inherited due to its similar optical and electronic properties with CIGS.Shafaat Ahmed et al. have demonstrated an efficiency of7.3%using the CZT alloy thin film deposited by electrodeposition. This indicates the wide applications of CZTS thin films.For obtaining the high quality CIGS thin films through optimization the electrodeposition parametersand developing the earth-abundant CZTS thin films, the three main researches are performed byelectrodepostion in potentiostatic mode, which listed as follows:(1) The CZT alloy was deposited on FTO substrate in potentiostatic mode using the PS-12electrodeposition setup. Then the CZT alloy thin films were sulfide under high temperature to fabricateCZTS thin films. The annealing times and annealing temperatures were optimized for obtaining highquality CZTS thin films. Our results showed that the high compact thin films were obtained bysulfuration annealed at580℃for60min.In order to evaluate their photovoltaic activities, theobtained CZTS films were introduced into the quantum-dots sensitized solar cells (QDSSCs) ascounter electrodes. The highest photoelectric conversion efficiency of1.60%was obtained by thesample sulfurized at580℃for60min.(2) The thin film was deposited on FTO substrate by one step electrodeposition. The influences of rapidannealing temperature of sulfuration on the performances of the thin films were investigated. Theinfluences of different deposition potential on the optical properties, morphologies, and composition ofthe thin film were also studied. CIS precursor films with low crystallinity were obtained by changingthe deposition potential and then the OVC phase appeared, which caused by the copper absence. Thedegree of sulfur replaced by selenium in film composition increased with the increaseing of sulfurizedtemperature.(3) TiO2nanowires array was fabricated by solvothermal growth method. The CdS buffer layer wasdeposited on the surface of TiO2nanowires by chemical bath deposition (CBD), through which theTiO2/CdS composite nanowires array was obtined. The CIS layer was deposited on the TiO2/CdScomposite nanowires array followed by sulfurizing at350℃for10min. The influences of CdSdeposition time on the performances of solar cells were investigated. Also, the influences of CISdeposition potential on the photoelectric conversion efficiency of the solar cells were studied. Wefound that the solar cells obtained the highest photoelectric conversion efficiency of1.33%wasachieved for the sample with CdS deposited for4min time. These results indicated the electro-deposition method is a simple and low-cost methods to prepare high quality CIS thin film solar cells...