High efficiency lead-free AlSb/KSnI3-ACIGS monolithic 2 T tandem solar cells with theoretical efficiency above 39 percent

Abstract This study presents the optimization and performance analysis of a tandem solar cell structure with the solar cell capacitance simulator in one dimension (SCAPS-1D). The novel monolithic two-terminal (2 T) tandem structure consists of an AlSb/KSnI3 double absorber multi-junction top cell and an ACIGS bottom cell. The top cell performance after optimizing yielded a power conversion efficiency (PCE) of 25.91% without any electron transport layer (ETL), and MoO3 is found to be the best hole transport layer (HTL) material. The effects of varying AlSb and KSnI3 absorber layer thickness, doping concentration (N D , N A ), and defect density (N t ) are also explored to identify the optimal parameters for the top cell. For the bottom cell, a graded ACIGS ((Ag,Cu)(In1-xGax)Se2)-based cell is utilized with a PCE of 21.89%. The tandem (2 T) device, incorporating these optimized top and bottom cells, achieved an overall PCE of 39.92%, with an open circuit voltage (V OC ) of 1.98 V, short-circuit current density (J SC ) of 24.49 mA/cm2, and fill factor (FF) of 82.39%. The incorporation of the ACIGS-based bottom cell demonstrates a significant improvement in PCE over the multi-junction top cell. This study makes a significant contribution to the advancement of lead-free perovskite/thin-film tandem solar cells.