Theoretical Analysis of the Effects of Band Gaps and the Conduction Band Offset of ZnS-CIGS Layers, as Well as Defect Layer Thickness

This article deals with solar cells based on CuIn, Ga) Se2 (CIGS) without the toxic cadmium buffer. The software named AFORS-HET is used to simulate the solar cell, n-ZnS/p-CIGS, in the structure n-ZnOAl/i-ZnO/n-ZnS/p-CIGS/Mo. The Ga-content of the CuIn1-xGaxSe2 absorber is x = 0.31 with an energy band gap of 1.19 eV. The optimum conversion efficiency achieved is found to be 26 %. The simulation results have shown that the ZnS buffer layer band gap does not influence the solar cell performance. On the other hand, the cell characteristic parameters were found to be more sensitive to the CIGS layer band gap variation and conduction band offset. We also analyse the effects of the band gap and thickness of the defect layer on the solar cell performance. The optimum band gap and thickness were found to be equal to 1.25 eV and 15 nm respectively.