This paper explores and compares the characteristics of eight different kinds of Cu(In, Ga)Se2 (CIGS) solar cells. Through the technique of chemical bath deposition (CBD), single- (i-ZnO) and double-layer (ZnS/CdS) CIGS cells were prepared and evaluated. The results of this research signify the potential of high-performance CIGS cells for photovoltaic (PV) industrial applications. This study focused on the growth-dependency and optical properties of ZnS/CdS-buffer stacked thin films, which were prepared through the CBD process. The best sample developed from this process consisted of a double-layer buffer and no i-ZnO layer. This sample yielded a conversion efficiency (η) of 9.23% and a short-circuit current density (JSC) of 26.72 mA/cm2. The performance of this sample was about 25% (absolute gain) better than that of the standard CdS cells. Furthermore, the average quantum efficiency in the short wavelength range (350–500 nm) for two of the ZnS/CdS buffer structures was 6.8% better than that of a single-layer CdS cell. This improvement can be attributed to the anti-reflective effect of the ZnS/CdS buffer structure, which increases the light-intensity incident on the main absorption layer. In addition, the ZnS/CdS-buffer layer not only eliminates the need for an i-ZnO layer but also reduces the usage of toxic Cd. The procedures to develop these flexible CIGS cells containing a ZnS/CdS buffer structure are simple, efficient, and reliable. These eco-friendly cells could be effectively applied to mass production for commercial PV applications.
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