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

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.