Entire mirror-like perovskite films for high-performance perovskite solar cells: The role of polar anti-solvent sec-pentyl alcohol

High-quality perovskite films are essential for high-performance perovskite solar cells (PSCs). Here we first proposed a polar anti-solvent technology of sec-pentyl alcohol (2-PA) for the fabrication of perovskite films. Our investigations have proven that 2-PA, as a better anti-solvent than conventional those with non- and high-polarity, enables the fabrication of uniform and dense perovskite films with mirror-like surface and film-through large grains. We found that moderate polar solvent more advantageously influences the crystallinity and morphology of perovskite films by extracting thoroughly the residual solvent and promoting a more complete and fast transformation from the lead polyhalide framework to the targeted perovskite film. By our proposed way, the best performing PSCs based on methylammonium lead iodide showed a power conversion efficiency (PCE) of over 17% under AM 1.5G illumination with high reproducibility and no photocurrent hysteresis. Our investigation indicates that sec-pentyl alcohol as anti-solvent could be an universal method for the preparation of hybrid organic-inorganic perovskite film.