Electrodeposition of Cu 2 ZnSnS 4 Thin Films Using Ionic Liquids
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1123-P05-06
Electrodeposition of Cu2ZnSnS4 Thin Films Using Ionic Liquids C.P.Chan1, H. Lam1, K.Y. Wong2 and C. Surya1,* 1
Department of Electronic and Information Engineering and Photonics Research Centre
The Hong Kong Polytechnic University, Hong Kong, China 2
Department of Applied Biology and Chemical Technology,
The Hong Kong Polytechnic University, Hong Kong, China * Corresponding author ABSTRACT We report the growth of Cu2ZnSnS4 (CZTS) thin films by electrodeposition in ionic liquid. Sulfurization was performed in elementary sulfur vapor environment at 450°C for 2 hours. The X-ray diffraction analysis indicated that the film has a stannite structure with preferred grain orientation along (112). Photo-absorption measurement of the sample was performed from 500 nm to 990 nm. It is found that the energy bandgap of the film is about 1.49eV and the absorption coefficient is found to be of the order of 104cm-1. INTRODUCTION It is highly desirable to fabricate high conversion efficiency solar materials at low cost. Among the thin film photovoltaic materials, copper-based chalcopyrite, copper indium gallium selenide (CIGSe) absorbers have been intensively studied in the past decade [1]. Laboratory CIGSe solar cells show high conversion efficiency of 19.9% [2] and high optical absorption coefficient. While CIGSe-based photovoltaic cells demonstrate desirable optoelectronic properties for the development of high-efficiency cells, the mass production of devices faces difficulties on the scarcity of indium and toxicity of selenium, leading to a concern for its viability for large-scale deployment. Recently, Copper-Zinc-Tin-Sulfide (CZTS), has attracted growing attention as a potential photovoltaic material due to the high absorption coefficient of the film, the abundance and the non-toxicity of the constituent elements, making large-scale deployment of the device a feasibility.
Vacuum deposition methods by electron beam and sputtering techniques have been widely investigated for the preparation of CZTS and other photovoltaic materials, but these techniques involve high capital investment, thus only applicable to high value niche markets. For this reason, electrodeposition of semiconductors has emerged as an alternative method for preparing thin film solar cell materials. The advantages of the electrodeposition technique are: i.) the process does not involve expensive vacuum modules; ii.) the technique provides excellent utilization of the raw materials; and iii.) the possibility of large area deposition of the material. The success development of the technique may lead to significant lowering in the cost of the materials. The use of ionic liquids as the electrolyte for the deposition process offers some promising benefits over the commonly used aqueous solutions [3]. The ionic liquid used in this experiment are both air and water stable, which has negligible vapor pressure up to 130°C, allowing film deposition at high temperatures. Moreover, the electrolyte has an electrochemical potential window of 2.5 V (-1.25V t
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