Stabilizing γ‐CsPbI3 Perovskite via Phenylethylammonium for Efficient Solar Cells with Open‐Circuit Voltage over 1.3 V

Cesium lead iodide (CsPbI3) perovskite has gained great attention due to its potential thermal stability and appropriate bandgap (≈1.73 eV) for tandem cells. However, the moisture‐induced thermodynamically unstable phase and large open‐circuit voltage (VOC) deficit and also the low efficiency seriously limit its further development. Herein, long chain phenylethylammonium (PEA) is utilized into CsPbI3 perovskite to stabilize the orthorhombic black perovskite phase (γ‐CsPbI3) under ambient condition. Furthermore, the moderate lead acetate (Pb(OAc)2) is controlled to combine with phenylethylammonium iodide to form the 2D perovskite, which can dramatically suppress the charge recombination in CsPbI3. Unprecedentedly, the resulted CsPbI3 solar cells achieve a 17% power conversion efficiency with a record VOC of 1.33 V, the VOC deficit is only 0.38 V, which is close to those in organic‐inorganic perovskite solar cells (PSCs). Meanwhile, the PEA modified device maintains 94% of its initial efficiency after exceeding 2000 h of storage in the low‐humidity controlled environment without encapsulation. By introducing moderate phenylethylammonium iodide and lead acetate in CsPbI3 perovksite, moiture resistance and charge recombination are optimized. The device achieves a 17% power conversion efficiency, a 1.33 V open‐circuit voltage (VOC) and the smallest 0.38 V VOC deficit. Meanwhile, the device maintains 94% of its efficiency after 2000 h storage in ambient environment.