Universal Approach for Managing Iodine Migration in Inverted Single‐Junction and Tandem Perovskite Solar Cells

Abstract Despite significant progress in the power‐conversion efficiency (PCE) of perovskite solar cells (PSCs), the instability of devices remains a considerable obstacle for commercial applications. This instability primarily originates from the migration of halide ions—particularly iodide ions (I⁻). Under light exposure and thermal stress, I⁻ migrates and transforms into I₂, leading to irreversible degradation and performance loss. To address this issue, we introduced the additive 2,1,3‐benzothiadiazole,5,6‐difluoro‐4,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl) (BT2F‐2B) into the perovskite. The strong coordination between the unhybridized p orbital and lone‐pair electrons from I⁻ inhibits the deprotonation of MAI/FAI and the subsequent conversion of I⁻ to I₂. The highly electronegative fluorine enhances its electrostatic interaction with I⁻. Consequently, the synergistic effect of BT2F‐2B effectively suppresses the decomposition of perovskite and the defect density of the iodide vacancies. This approach delivers a PCE over 26% for inverted single‐junction PSCs, with exceptional operational stability. According to the ISOS‐L‐3 testing protocol (maximum power point tracking at 85 °C and 50% relative humidity), treated PSCs retain 85% of their original PCE after 1000 h of aging. When the BT2F‐2B is applied to a wide‐bandgap (1.77 eV) perovskite system, the PCE of all‐perovskite tandem solar cells reaches 27.8%, confirming the universality of the proposed strategy.