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.