High‐Quality Lead Acetate–Based Ruddlesden–Popper Perovskite Films for Efficient Solar Cells

The 2D Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, are emerging photovoltaic materials because of their highly tunable optoelectronic properties and improved stability compared to their 3D counterparts. Nonhalide lead sources attract increasing attention in 3D perovskites, whereas the lead sources for RPPs are limited to lead halides. Herein, nonhalide lead source of lead acetate is investigated for high‐quality RPP films by a dimethyl sulfoxide (DMSO)‐assisted delayed annealing process. The incorporation of DMSO in the lead acetate–based precursor solution regulates the crystallization process, resulting in RPP films with distinctly enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution. Consequently, the optimized RPP solar cell with an inverted planar structure delivers a champion power conversion efficiency of 17.3%. Herein, future developments of nonhalide lead sources are spurred to fabricate RPP films with high device performance. Nonhalide lead source of lead acetate is developed for fabricating high‐quality Ruddlesden–Popper perovskite films for efficient solar cells. By introducing dimethyl sulfoxide in the lead acetate–based precursor solution to regulate the crystallization process, the film exhibits significantly improved quality with enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution.