Synergistic Dual-Halide Anion Engineering for Efficient Interface Passivation in 1.68 eV Wide-Bandgap Perovskite Solar Cells for Indoor Photovoltaics

Wide-bandgap (1.68 eV) perovskite solar cells (PSCs) are considered promising candidates for indoor photovoltaics due to their favorable optical properties. However, their power conversion efficiency (PCE) is significantly constrained by large open-circuit voltage (<i>V</i>_OC) losses, which primarily originate from intrinsic halide vacancy defects and uncoordinated Pb²⁺ located at the surface and grain boundaries of the perovskite films. Additionally, the energy level mismatches at the perovskite/electron transport layer (ETL) interface further aggravate <i>V</i>_OC losses by promoting nonradiative recombination. Herein, we report a synergistic dual-halide interface passivation strategy based on methylammonium iodide (MAI) and methylammonium chloride (MACl), in which the two halides play complementary and mechanistically distinct roles. MAI effectively reacts with and converts residual surface PbI₂ into the perovskite phase, while simultaneously passivating iodine-related vacancy defects. In parallel, MACl induces beneficial chloride incorporation at the interface, enabling slight bandgap broadening and producing a favorable vacuum-level shift that optimizes energy-level alignment between the perovskite and electron transport layer. When applied together, MAI and MACl deliver a cooperative passivation effect, substantially suppressing nonradiative recombination, prolonging carrier lifetimes, and facilitating more efficient charge extraction. As a result, the optimized 1.68 eV PSCs achieve a notable PCE of 20.41% with a <i>V</i>_OC of 1.262 V under standard AM 1.5G illumination, surpassing the untreated counterparts that achieve 18.48% with a <i>V</i>_OC of 1.169 V. More importantly, under indoor lighting conditions, the modified PSCs exhibit outstanding performance, delivering PCEs of 36.74 and 32.36% under 1000 and 200 lx LED illumination, respectively, demonstrating their strong potential for indoor photovoltaics.