Crowning Lithium Ions in Hole-Transport Layer toward Stable Perovskite Solar Cells.

State-of-the-art perovskite solar cells (PSCs) exhibit comparable power conversion efficiency (PCE) to that of silicon photovoltaic devices. However, the device stability remains a major obstacle that restricts widespread application. Doping-induced hygroscopicity, ion diffusion, and use of polar solvents in the hole-transport layer are detrimental factors for performance degradation of PSCs. Here, phase-transfer-catalyzed LiTFSI doping in Spiro-OMeTAD is developed to address these negative impacts. 12-Crown-4 as an efficient phase-transfer catalyst promotes the dissolution of LiTFSI without requiring acetonitrile. A combined experimental and theoretical study demonstrates the host-guest interaction between Li ions and 12-crown-4. Crowning Li ions by forming more stable and less diffusive crown-ether-Li complexes retards the generation of hygroscopic lithium oxides and mitigates Li -ion migration. Optimized PSCs deliver enhanced PCE and significantly improved stability under humid and thermal conditions compared with a control device. This method can also be applied to dope π-conjugated polymer. The findings provide a facile avenue to improve the long-term stability of PSCs.