UV-illuminated chemical bath deposition of CdS buffer layer for CIGSSe solar cells

In this paper, we compare the performance of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells with a CdS buffer layer grown by chemical bath deposition (CBD) with UV irradiation of 365 nm or 254 nm at an output power of 8 W. The effects of UV light irradiation on the CBD-CdS thin film deposition mechanism were investigated through chemical and electro-optical studies. UV light irradiation during the solution process promotes the hydrolysis of thiourea, thereby inhibiting the formation of the intermediate products being developed on the reaction pathways and decreasing the solution pH. Therefore, the efficiency of the CdS/CIGSSe solar cells was improved because of the increased elemental ratio of S/(S + O) in the CdS thin film. This very simple and effective approach can be used to control the S/O ratio of the CdS thin film fabricated by the CBD process without artificially controlling the process temperature, solution pH or concentration. When the UV light is irradiated in the CBD-CdS process, the hydrolysis of the TU in the CBD solution is accelerated and Cd(OH)2 formation is reduced. Therefore, the S/(S + O) ratio in CdS film is high and large cluster is minimized. Therefore, irradiation of UV light during CBD-CdS process is an effective method to obtain uniform and excellent CdS thin film. [Display omitted]