CIGS absorber layer with double grading Ga profile for highly efficient solar cells

Abstract

It is well-known that the band gap grading in CIGS solar cells is crucial for achieving highly efficient solar cells. We stimulate a CIGS solar cell and investigate the effects of the band gap grading on performance of the CIGS solar cell, where Ga/(Ga + In) ratio (GGI) at back (C_b) and front (C_f) of the absorber layer are considered constant. Our simulations show that by increasing the GGI at middle of CIGS absorber layer (C_m), the J_SC decreases and V_OC increases independent of the distance of the C_m from the back contact (X_m). For C_m lower than C_f, J_SC increases and V_OC decreases when the X_m shifts to the front of the CIGS layer. The behavior of J_SC and V_OC became reverse for the case of C_m greater than C_f. Almost in all of the structures, efficiency and FF have same behaviors. Our simulations show that the highest efficiency is obtained at C_m = 0.8 and X_m = 200 nm.