Theoretical study of the effect of (CdS)1-x(ZnS)x buffer layer on the performance of CIGS solar cells

Photovoltaic solar cell is one of the most important renewable energy sources. Solar cells based on thin-film layers are
considered as promising photovoltaic and offer a number of interesting advantages compared to the bulk silicon devices. In
all thin-film solar cells, CdS layer is applied as a heterojunction partner with CdTe, CuInS2 and CuInGaS2 (CIGS). Adding
wide bandgap materials such as ZnS to CdS can led to increase the energy gap of CdS and allow more photons in short
wavelength to pass through it and reach the absorber layer. In this work, the effect of (CdS)1-x:(ZnS)x(x=0, 0.1, 0.2, 0.3, 0.4
and 0.5) on the performance of CIGS solar cells are studied theoretically. The short-circuit current density (JSC), open-circuit
voltage (Vo), fill factor (FF) and the cell efficiency (η) have been estimated. The optical and recombination losses have been
taken into consideration. Adding ZnS to CdS leads to a significant improvement in the performance of CIGS solar cells. Our
results show that at x-ratio equals 0.5, the JSC increases by 18% and the optical losses decrease by more than 25%. The
optical losses have significant effect on JSC more than the effect of recombination losses. The CIGS efficiency increases
from 14.7% to 17.72% for x=0 and x=0.5, respectively.