Ion migration suppression mechanism via 4-sulfobenzoic acid monopotassium salt for 22.7% stable perovskite solar cells

The deep-level traps at grain boundaries (GBs) and halide ion migration are quite challenging for further enhancement of the stability and efficiency of perovskite solar cells (PSCs) as well as for the elimination of notorious hysteresis. Herein, we report a large-sized strongly coordinated organic anion GB anchoring strategy for suppressing ion migration and passivating defects in planar PSCs. The practical implementation of this strategy involves the incorporation of potassium salts containing a large-sized organic counter anion (4-sulfobenzoic acid monopotassium salt, SAMS) into the perovskite precursor. It has been found that anions within SAMS can be firmly anchored at GBs due to the strong coordination interaction between C=O and/or S=O at both ends of bulky anion and undercoordinated Pb2+ and/or halide vacancies, along with the hydrogen bond between −OH and formamidinium. SAMS can not only passivate shallow-level defects but also cause more effective passivation of the deep-level defects. The GB manipulation strategy results in a reduced defect density, an increased carrier lifetime as well as suppressed ion migration, which in turn contributed to enhanced efficiency and stability of PSCs together with a thorough elimination of hysteresis. As a result, the SAMS-modified device with an outstanding fill factor of 0.84 delivers a significant improvement in efficiency (22.7%) in comparison with the control device (20.3%). The unencapsulated modified device demonstrates only little degradation after 1320 h at 60°C.