銅銦鎵硒薄膜太陽能電池中化學水浴法製備之硫化鋅緩衝層製程技術優化

Abstract

銅銦鎵硒是一種具有潛力的薄漠太陽能電池材料，目前其最高轉換效率達到20.3%。然而在高效率太陽能電池的生產過程中，其緩衝層材料所使用的硫化鎘由於包含了鎘的成分，在電池年限到達之後將會對環境造成汙染。因此本論文提出對環境影響較小，同時不會嚴重降低電池效率的緩衝材料硫化鋅。由於硫化鋅本身是活性較低的材料，不容易在銅銦鎵硒吸收層上形成高覆蓋率與適當鋅硫化學當量比的薄膜，因此本論文針對化學水浴法製備之硫化鋅緩衝層做研究，包含了薄膜覆蓋率、鋅與硫化學當量比、薄膜厚度三者的改善。論文中首先研究了溶液中的溫度、氨水濃度、沉積時間對薄膜品質的影響，經由分析硫化鋅在化學水浴法中的沉膜機制後，提出了兩種增進成膜品質的方法，分別為「後處理製程」與「兩階段製程」。進一步研究「後處理製程」與「兩階段製程」發現兩階段製程可以有效增進硫化鋅的成膜品質，硫化鋅的兩階段製程在銅銦鎵硒吸收層上只需沉積大約100奈米的薄膜厚度即可達到了超過95 %的薄膜覆蓋率、1.78鋅與硫化學當量比。

Thin film Copper Indium Gallium Diselenide CIGS (CIGS) solar cells are one of the most promising candidates. Until now, the latest world record CIGS solar cell has achieved 20.3 % in efficiency. However, in CIGS solar cells fabrication, the use of cadmium sulfide as buffer layer in CIGS solar cells contaminates the environments when the solar cell panels reach lifetime. Therefore, the buffer material zinc sulfide (ZnS) which rarely affects the environments and does not decrease the cell efficiency largely was studied in this thesis. ZnS is a low activation material, so it is difficult to deposit high coverage and suitable stoichiometric ratio ZnS thin-film on CIGS absorber layer. Therefore, the aim of this study is to develop a deposition method for the ZnS buffer layer to reach desired Zn/S stoichiometric ratio and to improve coverage properties by using chemical bath deposition (CBD). Firstly, the temperature, the ammonia concentration, and the deposition time in chemical bath solution were investigated on the film properties. By analyzing the ZnS film growth mechanism in CBD method, two deposition methods, post-deposition and two-step deposition, are proposed. Through further investigation of the post-deposition and the two-step deposition, the two-step deposition method improves the ZnS film properties effectively. The ZnS film deposited by two-step deposition only needs to deposit about 100 nm thickness and then can reach over 95 % coverage properties and 1.78 Zn/S stoichiometric ratios on CIGS absorber layer.