Spontaneous grain polymerization for efficient and stable perovskite solar cells

Spontaneous grain polymerization strategy is proposed to fabricate efficient and stable perovskite solar cells (PSCs) through the incorporation of polymerizable additive ethyl 2-cyanoacrylate (E2CA). E2CA lies in and chemically anchors to grain boundaries (GBs) owing to –CN and -C=O groups’ coordination with PbI ₂ , thus passivating the defects at GBs and leading to high devices efficiency of 21.03%. Importantly, E2CA in perovskite films will spontaneously polymerize to a hydrophobic polymer at GBs when exposed in moisture air, thus blocking GBs channel for moisture penetration and enhancing the moisture-resisting properties of perovskite films. As a result, PSCs with E2CA exhibit superior stability in moisture air (relative humidity: 40–60%), retaining ~90% of the maximum efficiency after aging over 1000 h. Even under high temperature (85 °C) in moisture air, non-encapsulated MAPbI ₃ -E2CA devices still show good stability despite the burn-in degradation, retaining over 90% of the post burn-in efficiency after aging 200 h.