Cooperation of Dual Organic Spacers and A Site Cations for High‐Performance Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

n = 4 quasi-2D RP perovskite solar cells from 12.51 to 15.68% is achieved. Additionally, the unencapsulated devices retain 80.4% of initial efficiency after 1100 h of heating at 60 °C in ambient air with 40% relative humidity, demonstrating excellent thermal and moisture stability.