The ability to reduce energy loss at semiconductor surfaces through passivation or surface field engineering is an essential step in the manufacturing of efficient photovoltaic (PV) and optoelectronic devices. Similarly, surface modification of emerging halide perovskites with quasi-two-dimensional (2D) heterostructures is now ubiquitous to achieve PV power conversion efficiencies (PCEs) >25%, yet a fundamental understanding to how these treatments function is still generally lacking. Here we use a unique combination of depth-sensitive nanoscale characterization techniques to uncover a tunable passivation strategy and mechanism found in perovskite PV devices that were the first to reach the >25% PCE milestone. Namely, treatment with hexylammonium bromide leads to the simultaneous formation of an iodide-rich 2D layer along with a Br halide gradient that extends from defective surfaces and grain boundaries into the bulk three-dimensional (3D) layer. This interface can be optimized to extend the charge carrier lifetime to record values >30 μs and to reduce interfacial recombination velocities to values as low as <7 cm s⁻¹.

通过钝化或表面场工程减少半导体表面能量损失的能力是制造高效光伏 (PV) 和光电器件的重要步骤。同样，新兴的具有准二维 (2D) 异质结构的卤化物钙钛矿的表面改性现在已经普遍存在，以实现光伏发电转换效率 (PCE) > 25%，但对这些处理如何发挥作用的基本了解仍然普遍缺乏。在这里，我们使用深度敏感纳米级表征技术的独特组合来揭示钙钛矿光伏器件中的可调钝化策略和机制，这些器件是第一个达到 > 25% PCE 里程碑的器件。也就是说，用己基溴化铵处理会同时形成富含碘化物的 2D 层以及从缺陷表面和晶界延伸到体三维 (3D) 层的 Br 卤化物梯度。该界面可以被优化以将载流子寿命延长至记录值>30μs，并将界面复合速度降低至低至<7cm s ^-1的值。