Fabrication Of Cu2Znsn(S_Xse_1-X)₄Thin Film Solar Cells Via Sol-gel Route

Chalcogenide semicondouctor material, Cu2ZnSn(SxSe1-x)4(CZTSSe) has been confirmed as a alternative with broad application potential for thin film solar cells because it not only exhibits suitable optical and electrical properties similar to CIGS, but also consists of earth-abundant elements. Remarkable progresses have been made over the past few years by lots of groups using different fabrication approaches including vacuum based approaches and non-vacuum based techniques. Among various preparation approaches, sol-gel technique has the advantage of simple technology, low-cost, non-toxic and suitable for large-area production. To this dissertation proposed a method based on the sol-gel process to synthesize CZTSSe thin film and solar cells and demonstrated a highest power conversion efficiency of8.08%(active cell area) in this way. The main conclusions obtained are listed as following:(1) The CZTSSe thin films were prepared by annealing precursor thin film in a selenium atmosphere based on sol-gel method. The effects of the temperature of selenium, annealing temperature, annealing time and the ratio of metallic composition on the film quality were also investigated. A possible mechanism for the recrystallization of CZTSSe was proposed.The ratio of S/(S+Se) was regulated by controling the temperature of selenium. Besides, the optimal synthesis conditions were taken at the annealing temperature of560℃, the annealing time of40min, and The ratio of Cu/(Zn+Sn) and Zn/Sn was0.86and1.0respectively.(2) Through the photovoltaic tests on CZTSSe thin films with different ratio of S/(S+Se), The results illustrate that with the increase of Se, the short-circuit current of CZTSSe thin film solar cell increased while the open circuit voltage was reduced, the band gap was also reduced. The synthesis condition for CZTSSe cell with best conversion efficiency was taken at the ratio of S/(S+Se) of0.35.(3) The improved CZTSSe thin film solar cell get the highest photoelectric conversion efficiency of8.08%and a comprehensive analysis of the materials and device performance has been conducted. CZTSSe thin films have some grains extending from the bottom to the top of the CZTSSe layer with compositional profiling showing uniform metal composition. Between the Mo and CZTSSe layer there are obvious gaps and a relatively thick Mo(S,Se)2interfacial layer, the buffer layer CdS is also too thick, which indicated that there is still much room for improvement of CZTSSe cell devices.