Stabilizing γ‐CsPbI 3 Perovskite via Phenylethylammonium for Efficient Solar Cells with Open‐Circuit Voltage over 1.3 V

Cesium lead iodide (CsPbI 3 ) 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 ( V OC ) deficit and also the low efficiency seriously limit its further development. Herein, long chain phenylethylammonium (PEA) is utilized into CsPbI 3 perovskite to stabilize the orthorhombic black perovskite phase (γ‐CsPbI 3 ) 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 CsPbI 3 . Unprecedentedly, the resulted CsPbI 3 solar cells achieve a 17% power conversion efficiency with a record V OC of 1.33 V, the V OC 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.