Simulation of graded bandgap on backwall superstrate CIGS solar cells with MoOx electron reflection layer

摘要： A model of backwall superstrate CuInxGa(1?x)Se2 (CIGS) solar cell with MoOx as an electron reflection layer has been investigated by Solar Cell Capacitance Simulator (SCAPS). The influence of the CIGS absorber with different thicknesses on the performance of the CIGS solar cells with a flat bandgap structure is carefully analyzed. When the CIGS thickness is 400 nm, the device with 10 nm MoOx layer has the highest efficiency of 8.24%. To further increase the efficiency, a graded bandgap structure, near the MoOx layer, has been established, and the efficiency can be improved from 8.24% to 15.01% when the maximum bandgap value and the length of the graded region are 1.6 eV and 240 nm, respectively. The causes of efficiency enhancement by this graded bandgap structure are then studied. With an additional graded bangap structure in SCR, close to the CdS layer, the efficiency is slightly improved from 15.01% to 15.15%. Finally, the simulation results show that the efficiency can be increased from 15.15% to 16.26% when the thickness of MoOx is reduced from 10 nm to 1 nm.