Efficiency improvement of Cu(In(1−x)Ga x )Se2 solar cell using copper barium tin sulfide as back surface field layer and bandgap grading technique

This work proposes the simulation of graded CuIn1−xGaxSe2 –based solar cell with copper barium tin sulfide (CBTS) compounds as a back surface field (BSF) layer using the SCAPS-1D software. The CBTS BSF layer reduces the charge carrier losses on the back contact side and creates an extra BSF that helps in extracting holes toward the back contact. To utilize the maximum spectrum absorption range, three different grading configurations were analyzed by varying the stoichiometry of CuIn1−xGaxSe2 . This grading technique significantly improves the device performance such as open circuit voltage (V _oc), short circuit current density (J _sc), fill factor (FF), and power conversion efficiency by changing the Ga content in the CIGS material. Furthermore, the impact of interface defect recombination velocity at the WSSe/graded-CIGS interface, acceptor density, and bulk defect in the CIGS layer on the device’s performance have been analyzed. The insertion of CBTS as a BSF layer and the bandgap grading technique yield a maximum efficiency of 31.08% for the proposed solar cell. These results will be helpful in the fabrication of highly efficient bandgap graded-CIGS solar cells.