Ruddlesden–Popper 2D Component to Stabilize γ‐CsPbI₃ Perovskite Phase for Stable and Efficient Photovoltaics

Abstract The highest certified power conversion efficiency (PCE) of black phase based CsPbI 3 perovskite solar cells has exceeded 18%, and become a hotspot in recent progress. However, the black phase of CsPbI 3 rapidly transforms to yellow phase in ambient conditions due to its thermodynamic instability. Here, a Ruddlesden–Popper 2D structure is introduced into γ‐CsPbI 3 film to stabilize the black phase via reducing dimensionality. It is found that a judicious amount of phenylethylammonium iodide can adjust the dimensionality of γ‐CsPbI 3 film from 2D to quasi‐2D and 3D phase. Comprehensive consideration to obtain both the stability and high PCE, quasi‐2D ( n = 40) γ‐CsPbI 3 delivers a reproducible PCE of 13.65% with negligible hysteresis. By utilizing femtosecond…