Highly Stable Perovskite Solar Cells by Reducing Residual Water‐Induced Decomposition of Perovskite

Comprehensive Summary Residual water‐induced decomposition is one of the dominant reasons for the decay of power conversion efficiency (PCE) in perovskite solar cells (Pero‐SCs). To solve this problem, we introduce traces amount of sodium hyaluronate (SH) into the perovskite active layer to reduce the remaining water during the preparation of perovskite films. Unlike the traditionally adopted passive protection of perovskite from exterior water by low surface energy coatings, this study provides active control of the interior water by the addition of a water adsorbent into the perovskite films. The encapsulated Pero‐SCs with SH retain approximately 70% of their initial PCE in 4000 h, while those without SH retain 32% of their initial PCE in 1000 h under the dark and ambient atmosphere. The unencapsulated Pero‐SCs with SH stored in N 2 atmosphere maintain over 94% of the initial PCE in 3000 h at room temperature away from light and remain over 88% of the initial PCE in 2000 h even the devices are heated to 70 °C. It has been proven that the improved stability is mainly due to the well‐controlled residual water in perovskite films. Concomitantly, the PCE of p‐i‐n solar cells based on (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 is improved from 19.34% to 21.54%.