Immobilizing Surface Halide in Perovskite Solar Cells via Calix[4]pyrrole

Halide diffusion across the charge-transporting layer followed by a reaction with metal electrode represents a critical factor limiting the long-term stability of perovskite solar cells (PSCs). In this work, a supramolecular strategy with surface anion complexation is reported for enhancing the light and thermal stability of perovskite films, as well as devices. Calix[4]pyrrole (C[4]P) is demonstrated as a unique anion-binding agent for stabilizing the structure of perovskite by anchoring surface halides, which increases the activation energy for halide migration, thus effectively suppressing the halide-metal electrode reactions. The C[4]P-stabilized perovskite films preserve their initial morphology after ageing at 85 °C or under 1 sun illumination in humid air over 50 h, significantly outperforming the control samples. This strategy radically tackles the halide outward-diffusion issue without sacrificing charge extraction. Inverted-structured PSCs based on C[4]P modified formamidinium-cesium perovskite exhibit a champion power conversion efficiency of over 23%. The lifespans of unsealed PSCs are unprecedentedly prolonged from dozens of hours to over 2000 h under operation (ISOS-L-1) and 85 °C ageing (ISOS-D-2). When subjected to a harsher protocol of ISOS-L-2 with both light and thermal stresses, the C[4]P-based PSCs maintain 87% of original efficiency after ageing for 500 h.