Bilayer CIGS-based solar cell device for enhanced performance: a numerical approach

Abstract

A numerical simulation of a single-junction bilayer of CIGS-based solar cell tandem device is presented in this paper. The structure used here is Al:ZnO/CdS/CuIn1-XGaXSe2/CuIn1-YGaYSe2, and the software used is wx-AMPS. As most of the efficient high-performance photovoltaic devices are strongly dependent upon Ga content, the variation of Ga ratio is a necessary approach in the investigation of CIGS solar cells. As a result, different Ga grading profiles have been demonstrated and thoroughly analyzed the different solar cell parameters viz. open-circuit voltage (Voc), short-circuit current density(Jsc), fill factor, external quantum efficiency and efficiency (η) of the above structure under AM 1.5 illumination. At an initial process, we analyzed the single layer of CIGS (CuIn0.69Ga0.31Se2) solar cell device and its output characteristics. In the second step, we have shown the impact of tandem structure with the addition of a second CIGS absorber layer with different Ga concentrations and its improved performance as compared with a single absorber layer device. We also proposed for the first time a solution to the issue of diffusion (unintentional Ga grading) which occurs at the time of annealing at higher temperatures by adding a p-type MoS2 layer in between the bilayer CIGS to limit the diffusion and to achieve the proposed grading. The efficiency of the bilayer device structure with fixed Ga fraction x = (0.31) of the top absorber layer along with Ga fraction y = (0.45) of the bottom absorber layer shows the improved efficiency from 20.56% (single layer) to 23.6% (bilayer). Addition of a p-type MoS2 layer in between the bilayer CIGS further improves the efficiency from 23.6 to 24.17%.