Dibenzo‐18‐Crown‐6‐Assisted Inhibition of Cation Migration for Stable Perovskite Solar Cells

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Formamidinium–cesium (FACs)‐based perovskites are potential light‐absorbing materials for stable perovskite solar cells (PSCs), while long‐term stability deterioration caused by photo‐ and moisture‐induced cation migration and phase separation restrict their further commercial application. Herein, crown ether molecules with both, an electronegative cavity and a negatively charged π bond, dibenzo‐18‐crown‐6 (DB18C6), are introduced to FACsPbI 3 films aiming at gaining better capability of inhibiting cation migration benefiting from the crown ether–cation complexation. Meanwhile, 18‐crown‐6 (18C6) with an electronegative cavity‐only is also employed for comparison. By tracing the changes of UV–vis absorption spectra, steady‐state photoluminescence, and Kelvin probe force microscopy of perovskite films under 24 h continuous light soaking, it is observed that the DB18C6‐modified FACsPbI 3 film shows remarkably negligible degradation, in comparison with the unmodified and 18C6‐modified FACsPbI 3 films. As a result, DB18C6‐modified PSCs with the architecture of ITO/SnO 2 /FACsPbI 3 /Spiro‐OMeTAD/Ag achieve an enhanced power conversion efficiency (PCE) exceeding 20.84%, which is a competitive efficiency for methylammonium‐free pure‐iodine n–i–p PSCs. The resultant unencapsulated DB18C6‐modified devices retain up to 94.73% and 90.18% of their original PCEs even after 500 h continuous full sunlight light soaking and 85 °C heating, respectively. Such crown ether modification provides a pathway on long‐term operational stabilized photovoltaics.