Analysis of Grading Induced Bandgap Variability and Defect States on Performance of CIGS Solar Cells Through Device Simulations

Grading of the band gap through the CIGS absorber layer has potential to improve the efficiency of the solar cell and the CIGS material has a feature of adjustable band gap. Therefore taking the advantage of that we varied the band gap of the CIGS material by changing the composition ratio of Ga/(Ga+In) and S/(S+Se). We simulated and analyzed the effect of band gap variations in CIGS layer, induced by grading of doping concentration profile and defect states over the performance of solar cell. The performance analysis was done using S CAPS-ID simulator. We found that the variable band gap in absorber layer provides an alternative to reduce the absorber layer thickness and yet achieve the comparable efficiency of the device. We observed the 2.48% efficiency increment by grading the CIGS material. This enhancement in efficiency is because of reduced recombination effect and increased no of generating excitons.