Abstract
In this study, zinc sulfide thin films are prepared by ammonia-free chemical bath deposition that we can find out the useful parameters applying to CuIn1-xGaxSe2 thin film solar cell. Use the zinc sulfate and thioacetamide (TAA) to be the sources of zinc ions and sulfur ions, respectively. In contrast to conventional process, adding ammonia as a complexing agent. Fabrication of ammonia-free also without any complexing agents CBD-ZnS buffer layer for CIGS was attempted. The total thesis can divide into three parts to optimize the ammonia-free CBD-ZnS buffer layer devices. The first part: A novel chemical approach that applied at room temperature to clean and passivate at the same time surface of CIGSe absorber before buffer layer deposition. By pre-treatment on CIGS surface with TAA acidic solution, oxides can be removed and additional S-containing layer forms, inducing remarkable enhancement in the electrical performances of the CIGS solar cells. The second part: the deposition times are controlled. we can fabricate an ultrathin also less Zn(OH)2 formation ZnS thin film by ammonia-free CBD process to form a rigid p-n heterojunction ; Also, light soaking is not needed in this process to optimize photovoltaic performance.The X-ray photoelectron spectroscopy (XPS) is used and measured that indicating the ZnS thin films formed by ammonia-free process revealed higher sulfur-to-oxygen ratio than ammonia process one. 30 minutes is choose for the ideal reaction time. The efficiency 9.16% was achieved without light soaking treatment. The third part: After ammonia-free CBD-ZnS buffer layer deposition, two different kinds of post-treatment are investigated. By post air-annealing, zinc may diffusion into bulk CIGS that result in the formation of buried p-n homo-junction, significantly improved cell performaces from 1.28% to 9.16%. With extra oxygen plasma treatment, higher sulfur-to-oxygen ratio ZnS thin film obtained by ammonia process may be reduced. Further, combined both oxygen plasma treatment with the post air-annealing, devices using ammonia-free CBD-ZnS buffer layer can reach 10.16%, which is almost the same as that of the cells pepared by ammonia process with 60 minutes light soaking treatment.