Design and Optimization of all-thin-film CdSe/Si Tandem Solar Cells Using SCAPS-1D Simulation

The pairing of thin-film cadmium selenide (CdSe) and silicon (Si) within tandem solar cell (TSC) structures offers a promising avenue to achieving high-efficiency, cost-effective, and flexible photovoltaic devices. Despite the favorable optoelectronic properties of CdSe and the reliability of Si, very little effort has been made on CdSe/Si tandem structures, particularly on the all-thin-film flexible arrangements, both experimentally and through computation work. Herein, we report an extensive numerical work using SCAPS-1D device simulator to design and optimize CdSe/Si TSCs. The work begins by calibrating standalone CdSe and flexible (20 µm) Si single-junction solar cells to establish accurate baseline models. Initial tandem structures are then integrated, and then the top CdSe cell is optimized. The optimization technique is subject to specific emphasis on selecting and evaluating various hole transport layer (HTL) structures to address the valence band offset (VBO) challenge between CdSe and HTL. The optimized two-terminal (2T) design is then simulated and presented. Starting from baseline calibrated CdSe and flexible Si cells, achieving 6.00% and 14.60% power conversion efficiencies (PCE), respectively, the resultant tandem structures exhibit enhanced overall PCE of up to 33% after current matching, demonstrating the potential of the CdSe/Si architecture for high-efficiency photovoltaic applications. This work provides critical insights into interface and material selection engineering and opens avenues to further experimental realization on flexible tandem solar technologies.