Two-dimensional Ruddlesden–Popper layered metal-halide perovskites have attracted increasing attention for their desirable optoelectronic properties and improved stability compared to their three-dimensional counterparts. However, such perovskites typically consist of multiple quantum wells with a random well width distribution. Here, we report phase-pure quantum wells with a single well width by introducing molten salt spacer n-butylamine acetate, instead of the traditional halide spacer n-butylamine iodide. Due to the strong ionic coordination between n-butylamine acetate and the perovskite framework, a gel of a uniformly distributed intermediate phase can be formed. This allows phase-pure quantum well films with microscale vertically aligned grains to crystallize from their respective intermediate phases. The resultant solar cells achieve a power conversion efficiency of 16.25% and a high open voltage of 1.31 V. After keeping them in 65 ± 10% humidity for 4,680 h, under operation at 85 °C for 558 h, or continuous light illumination for 1,100 h, the cells show <10% efficiency degradation.

二维Ruddlesden-Pop层状金属卤化物钙钛矿因其理想的光电性能和改进的稳定性而吸引了越来越多的关注，而它们的三维对应物则更高。然而，这种钙钛矿通常由具有随机阱宽度分布的多个量子阱组成。在这里，我们通过引入熔融盐间隔基乙酸正丁胺代替传统的卤化物间隔基碘化正丁胺，报道了具有单阱宽度的纯相量子阱。由于n之间的强离子配位可以形成乙酸丁胺和钙钛矿骨架，形成均匀分布的中间相的凝胶。这允许具有微米级垂直排列的晶粒的纯相量子阱膜从其各自的中间相结晶。所得太阳能电池的功率转换效率为16.25％，高开路电压为1.31V。将其在65±10％的湿度下保持4,680小时，在85°C下工作558小时，或连续光照1,100个之后h，电池显示出<10％的效率下降。