Analysis and improvement of CIGS solar cell efficiency using multiple absorber substances simultaneously

In this paper, the efficiency of a CIGS solar cell was increased in several stages. The common structure and configuration of the CIGS solar cell are the ZnO:Al/ZnO/CdS/CIGS/MO combination whose efficiency is optimized approximately 20% for CIGS with thickness of 2 mu m and 17% for CIGS with thickness of 1 mu m. In this article, thickness of CIGS is 1 mu m and the efficiency of this type of solar cell was calculated using Atlas software of Silvaco. In the first step, by applying Zn1-xMgxO material with x = 0.17 instead of ZnO material, the cell efficiency was 20.7% and then by adding GaAs as the electron reflector layer, we were able to achieve 27.1% efficiency and at the end, to increase the efficiency, one absorber layer is added under the CIGS absorber. This absorber layer is CIS (CIS is CuInSe2) that made the efficiency to become 27.9%. Indeed, CIGS absorber layer is not able to absorb all photons of the sun. So, this added absorber layer is able to absorb a part of low-energy photons, which lead to increasing the efficiency of the solar cell. It should be noted that in the whole process of this article, CIGS and CIS absorber layers are p-type.