Controllable and innovative preparation of Zn(O,S) buffer layers for CIGS thin film solar cells

Abstract

The band gap of CdS (Eg = 2.4 eV) was narrow, which made it unable to transmit short-wave sunlight through the CIGS absorber layer. Zn(O,S) thin film, prepared by doping O into ZnS, had a wider band gap, and the raw material was green and non-toxic, making it suitable as a buffer layer for solar cells. However, CBD-Zn(O,S) usually takes longer than CdS deposition. In this work, By shortening the deposition time through the fast hydrolysis of TAA. Na3NTA was added in the solutions to improve the quality of Zn(O,S) thin films. The effect of Na3NTA concentration on the complex ion contents was investigated. When Na3NTA was added at a concentration of 0.04 M along with TAA (0.04 M), the film had a high T% of 88.6%, Eg of 3.76 eV, and a dense grain distribution. ZnS and ZnO grew at (111) and (100) crystals, respectively. Raman and XPS analyses showed the existence of Zn–S and Zn–O bonds, indicating the high crystalline quality of the Zn(O,S) thin films prepared with CBD. Finally, when the optimal concentrations of ZnSO4, NH4OH, Na3NTA, and TAA were 0.04 M, 0.48 M, 0.04 M, and 0.04 M, respectively, the prepared Zn(O,S) thin films could be used as a cadmium-free buffer layer for solar cells.