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 (PSCs) is commonly ascribed to elevated ion migration due to the low electronegativity of iodine. To address this issue, boric acid (BA) was chosen as a stabilizer for perovskite thin films. As a Lewis acid, the boric acid has an sp2 hybridized boron atom, which can readily accept a pair of electrons from the iodine ion in its 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. The inclusion of the BA stabilizer in PSCs resulted in an enhanced power conversion efficiency (PCE) of 25.52 %. The initial efficiency of the BA-modified device was remained at 80 % after 1000 hours at 85 degrees C 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.