Optical Coupling Optimization Enables Cost‐Effective Planar Silicon‐Perovskite Tandem Solar Cells

ABSTRACT Planar silicon/perovskite tandem solar cells exhibit significant advantages over textured architectures, including simplified fabrication, reduced cost, and scalability for industrial production. However, their planar configuration inherently leads to substantial optical losses. Here, we systematically analyze optical loss mechanisms in planar silicon/perovskite tandem devices and develop an optical simulation framework to address current‐matching challenges between sub‐cells. Through precise manipulation of hole transport layer thickness, we demonstrate synergistic optimization of parasitic absorption and reflection in the top cell. This approach yields a semi‐transparent device with a short‐circuit current density of 19.48 mA/cm² and a power conversion efficiency of 20.37%. An optical coupling model is established to determine optimal layer thicknesses under current‐matched conditions for a tandem device. For bifacial configurations, active layer thickness and bandgap are co‐optimized. Simulation results reveal that a 1.56 eV bandgap perovskite layer (800 nm) achieves 35.40% efficiency at 0.3 albedo. Cost analysis shows bifacial devices reduce the levelized cost of energy to $0.258/W at 0.3 albedo, representing a 12.8% reduction compared to single‐sided Ag‐coated counterparts. This study provides a comprehensive optical design strategy and cost‐performance evaluation, offering critical insights for developing next‐generation low‐cost, high‐efficiency tandem photovoltaic architectures.