Intralayer A-Site Compositional Engineering of Ruddlesden–Popper Perovskites for Thermostable and Efficient Solar Cells

Layered Ruddlesden–Popper (RP) perovskites have good moisture- and photostability. However, thermal stability of the RP perovskites is still a challenge. In this work, through a joint theoretical and experimental study, we report an intralayer A-site compositional engineering strategy to enhance the thermal stability of the RP perovskite solar cells. The triple-A-site-cation BA 2 (MA 0.76 FA 0.19 Cs 0.05 ) 3 Pb 4 I 13 (labeled as T-RP ) cells retain 80% of the initial efficiency after being stressed at a constant temperature of 85 °C for over 1400 h in the dark, which is a significant enhancement as compared to the FA-free or Cs-free double-A-site-cation reference devices. Enhanced stability is attributed to improved structural stability, film quality with larger and more compact micrometer grains, and lower trap densities of the T-RP, as compared to the double-A-site-cation RP perovskites. When appropriate excess PbI 2 is introduced in the T-RP layer, a power conversion efficiency of 15.58% is obtained for RP perovskite solar cells with high thermal stability.