Metal halide perovskites of the general formula ABX₃—where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion—have shown great potential as light harvesters for thin-film photovoltaics^1,2,3,4,5. Among a large number of compositions investigated, the cubic α-phase of formamidinium lead triiodide (FAPbI₃) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells^6,7,8,9, and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO⁻) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance.

通式 ABX ₃的金属卤化物钙钛矿——其中 A 是一价阳离子，例如铯、甲基铵或甲脒；B为二价铅、锡或锗；X 是一种卤化物阴离子——已显示出作为薄膜光伏^1,2,3,4,5的光收集器的巨大潜力。在大量研究的成分中，立方 α 相的甲脒三碘化铅 (FAPbI ₃ ) 已成为最有前途的高效稳定钙钛矿太阳能电池^6,7,8,9的半导体，并最大限度地发挥其性能这种设备中的材料对于钙钛矿研究界至关重要。在这里，我们介绍了一种使用拟卤化物阴离子甲酸盐（HCOO ^-) 以抑制存在于晶界和钙钛矿薄膜表面的阴离子空位缺陷并增加薄膜的结晶度。由此产生的太阳能电池器件的功率转换效率为 25.6%（经认证为 25.2%），具有长期运行稳定性（450 小时），并显示出强烈的电致发光，外部量子效率超过 10%。我们的研究结果为消除金属卤化物钙钛矿中存在的最丰富和最有害的晶格缺陷提供了直接途径，从而为获得具有改进光电性能的溶液可加工薄膜提供了便利。