High-performance perovskite/perovskite tandem solar cells require high-efficiency and stable low-bandgap perovskite subcells. State-of-the-art low-bandgap mixed tin–lead iodide perovskite solar cells exhibit either a high power-conversion efficiency or improved stability, but not both. Here we report a two-step bilayer interdiffusion growth process to simultaneously meet both requirements for formamidinium-based low-bandgap mixed tin–lead iodide perovskite solar cells. The bilayer interdiffusion growth process allows for the formation of high-quality and large-grained perovskite films with only 10 mol% volatile methylammonium. Additionally, one-dimensional pyrrolidinium perovskite was applied to passivate the perovskite film and improve the junction quality, which resulted in a carrier lifetime of 1.1 μs and an open circuit voltage of 0.865 V for our perovskite film and device with a bandgap of 1.28 eV. Our strategies enabled a power-conversion efficiency of 20.4% for low-bandgap perovskite solar cells under AM 1.5G illumination. More importantly, an encapsulated device can retain 92% of its initial efficiency after 450 h of continuous 1 sun illumination.

高性能钙钛矿/钙钛矿串联太阳能电池需要高效且稳定的低带隙钙钛矿子电池。先进的低带隙混合锡铅碘化物钙钛矿型太阳能电池具有高功率转换效率或改善的稳定性，但不能兼而有之。在这里，我们报告了两步双层互扩散生长过程，可以同时满足基于甲ami的低带隙混合锡铅碘化物钙钛矿太阳能电池的两个要求。双层互扩散生长工艺允许仅使用10 mol％的挥发性甲基铵形成高质量和大粒度的钙钛矿薄膜。此外，使用一维吡咯烷鎓钙钛矿钝化钙钛矿膜并改善结质量，从而导致载流子寿命为1.1μs和开路电压为0。我们的钙钛矿薄膜和器件的865 V带隙为1.28 eV。我们的策略可使AM 1.5G照明下的低带隙钙钛矿太阳能电池的功率转换效率达到20.4％。更重要的是，在连续1次日光照射450小时后，封装的设备可以保留其初始效率的92％。