The synergistic effect of A-site cation engineering and phase regulation enables efficient and stable Ruddlesden-Popper perovskite solar cells.

BA2(MA)n-1PbnI3n+1 series low-dimensional (2D) perovskites have been widely investigated for their remarkable environmental stability, but still suffer the poor light absorption and disordered phase distribution, hindering their practical applications. In this work, we combine the introduction of FA and the addition of PbCl2 to optimize the film quality, strengthen the light absorption, regulate internal phase distribution, and promote carrier transport inside 2D perovskite films. The incorporation of FA promotes sufficient light absorption and improve the film crystallinity. Furthermore, the addition of PbCl2 eliminates the low n phase (n = 1) and suppresses the forming of the low n phase of n = 2, enhancing the film conductivity and diminishing carrier recombination. The synergistic of A-site cation engineering and phase manipulation achieves a high efficiency of 16.48%. Importantly, the synergistic prepared perovskite film does not show any changes after 60 days in the air with an average humidity of 57%±3%, and the corresponding solar cell maintains 85% of the original efficiency after more than 800 hours, demonstrating remarkable environmental stability. The results indicate that the synergistic of A-site cation engineering and phase manipulation is promising for producing superior efficiency, along with satisfying humidity stability.