Modeling and Performance Improvement of Organic Tandem Solar Cells Using SCAPS-1D Simulator

This study presents a simulation-based optimization of a two-terminal (2T) all-polymer tandem solar cell using SCAPS-1D. The structure incorporates PM7:PIDT as the top sub-cell and PM6:PY-IT as the bottom sub-cell. Two key optimization strategies were investigated to enhance device performance. The first involved adjusting the top absorber's thickness and defect concentration, with optimal values of 200 nm and 10¹¹ cm⁻³, respectively. This configuration yielded a Jsc of 15.1 mA/cm², Voc of 2.11 V, FF of 76.7%, and a PCE of 24.5%. The second strategy focused on interfacial engineering by replacing the electron transport layers: TiO₂ was used in the bottom cell and PDINN in the top cell, resulting in Jsc = 11.77 mA/cm², Voc = 2.34 V, FF = 83.0%, and PCE = 22.8%. Both approaches outperformed the unoptimized reference device (PCE = 17.2%) and surpassed reported experimental benchmarks (~17.6%). The thickness-defect optimization alone led to a PCE gain of nearly 9%, underlining the importance of finely tuning material parameters and structure. These findings demonstrate the strong potential of all-polymer tandem solar cells for future flexible and lightweight photovoltaic applications, while offering valuable design guidelines for experimental implementation.