Enhanced Crystallinity of Low‐Temperature Solution‐Processed SnO2 for Highly Reproducible Planar Perovskite Solar Cells

Abstract Low‐temperature solution‐processed SnO 2 as a promising electron‐transport material for planar perovskite solar cells (PSCs) has attracted particular attention because of its outstanding properties such as high optical transparency or high electron mobility. However, low‐temperature sol–gel processes used in the synthesis are inevitably affected by the humidity of the atmosphere, which results in a wide distribution in the performance of the prepared PSCs owing to the inability to control crystallinity and defects. Herein, a highly crystalline SnO 2 film is synthesized using a simple water bath post‐treatment, which can remove the surface residuals of SnCl 4 on the SnO 2 films, which is beneficial for the interface charge transport from the perovskite to the SnO 2 electron‐transport layer. An improved performance of the PSCs can be easily obtained applying this treatment, giving rise to a high power conversion efficiency (PCE) of 19.17 %, much higher than that of the pristine SnO 2 ‐based device (17.59 %). Most importantly, the reproducibility of the devices has been greatly improved, independent of the environmental humidity. Therefore, the enhanced crystallinity of SnO 2 has shown promise for future commercial PSC applications: 5 cm×5 cm PSC modules have achieved a PCE of 16.16 %.