High-Efficiency Perovskite/Silicon Tandem Solar Cells Based on Wide-Bandgap Perovskite Solar Cells with Unprecedented Fill Factor

Abstract Recent progress in inverted perovskite solar cells (iPSCs) highlights the critical role of interface engineering between the charge transport layer and perovskite. Self-assembled monolayers (SAM) on transparent conductive oxide electrodes serve effectively as hole transport layers, though challenges such as energy mismatches and surface inhomogeneities remain. Here, a blended self-assembled monolayer of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and (4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) is developed, offering improved surface potential uniformity and interfacial energy alignment compared to individual SAMs. Interactions between the SAMs and ionic species are investigated with simulation analysis conducted, revealing the elimination of interfacial energy barriers through precise energy-level tuning. This strategy enables wide-bandgap (1.67 eV) perovskite solar cells with inverted structures with over 24% efficiency, an open-circuit voltage ( V oc ) of 1.268 V, and a certified fill factor (FF) of 86.8%, leading to a certified efficiency of 23.42%. The approach also enables high-efficiency semi-transparent devices and a mechanically stacked four-terminal perovskite/silicon tandem solar cell reaching 30.97% efficiency.