Towards highly efficient and stable perovskite solar cells: suppressing ion migration by inorganic boric acid stabilizer

The poor stability of organic-inorganic perovskite solar cells is commonly ascribed to elevated ion migration, stemming from the low electronegativity of iodine. To address this issue, boric acid was chosen as a stabilizer for perovskite thin films. As a Lewis acid, the boric acid has a sp² hybridized boron atom, which can readily accept a pair of electrons from iodine ion into their vacant unhybridized p orbital, and the formation of the Pb-O bond further increases the iodide migration barrier. The significantly increased barrier of the iodine ion migration was demonstrated by the improved phase stability of the perovskite film under an electric field and the obviously enhanced stability of the perovskite films under strong ultraviolet light. PSCs that included the BA stabilizer were able to achieve an enhanced PCE of 25.52%. The initial efficiency of BA-modified devices remained at 80% even after being aged for 1000 hours at 85 ℃ under around 30% relative humidity (RH). When subjected to maximum power point tracking and 20-25% RH, the PCE of BA-modified devices maintained an initial efficiency of 80% after 1500 hours.