High-Efficiency Design and Optimization of 2T Monolithic Polymer/Polymer Tandem Solar Cells Using SCAPS-1D Simulations

Abstract In this study, we present a novel 2T monolithic polymer/polymer tandem solar cell (TSC) model, drawing upon experimentally validated sub-cell designs composed entirely of OSC/OSC polymers. The individual sub-cells were calibrated against experimental data, resulting in power conversion efficiencies (PCE) of 10.33% for the front cell and 21.72% for the rear cell. The bottom cell incorporates a PM6:Y6 active layer in an ITO/Cu2O/PM6:Y6/SnO2/Ag configuration, while the top polymer cell is designed with conventional structure comprising ITO/PEDOT:PSS/PM7:PIDT/PDINN/Ag. Simulations were performed using the SCAPS 1D tool to individually optimize each sub-cell's performance. An extensive investigation was conducted on band alignment, defect density, active layer thickness, and the selection of electron and hole transport layers (ETLs and HTLs). Furthermore, we analyzed the effects of temperature, shunt resistance, and series resistance on the two sub-cells to enhance stability and performance. The resulting tandem structure demonstrated a short-circuit current density (JSC) of 11.685 mA/cm², an open-circuit voltage (VOC) of 2.0721 V, a fill factor of 82.823%, and a PCE of 20.054%, positioning it as a promising candidate for flexible, environmentally sustainable, and high-efficiency tandem solar cells. These findings underscore the potential of our design in advancing the performance benchmarks of organic tandem solar cells.