Cationic polarity facilitation with tailored aminopyridine ligands for bulkier defect-free and air-stable perovskite solar cells

Abstract

The presence of defective crystal frameworks in the bulk of formamidinium (FA)-dominant perovskites, combined with their inferior phase stability, compromises the efficiency, reliability and environmental robustness of perovskite solar cells (PSCs). Here, 2,6-bis(aminomethyl)pyridine (2,6-BAMPy) with strong passivation capability is exploited to construct a defect-free perovskite absorber. 2,6-BAMPy effectively minimizes the volatilization of FA materials and suppresses the halide-related defects at the perovskite surface through its terminal ammonium groups. Unlike other aminopyridine derivatives, specific polarity facilitation by 2,6-BAMPy triggers the desirable formation of a single stable isomer of the amidinium cation upon reaction with conjugated FA⁺, providing rationality in the optimization of bulkier perovskites. Moreover, the unique molecular geometry of 2,6-BAMPy energetically favors the formation of photoactive α-phase perovskites, effectively suppressing the unwanted intermediate phases throughout the crystallization process. As a consequence, the corresponding PSCs fabricated in open-air conditions deliver a champion efficiency of 24.16%. The encapsulated devices retain 91.2% of their initial performance after 2400 hours of accelerated damp-heating measurements (85 °C and 85% relative humidity).