Understanding semiconductor surface properties and manipulating them chemically are critical for improving their performance in optoelectronic devices. Hybrid halide perovskites have emerged as an exciting class of highly efficient solar materials; however, their device performance could be limited by undesirable surface properties that impede carrier transport and induce recombination. Here we show that surface functionalization of methylammonium lead iodide (MAPbI3) perovskite with phenethylammonium iodide (PEAI), a commonly employed spacer cation in two-dimensional perovskites, can enhance carrier diffusion in the near-surface regions and reduce defect density by more than one order of magnitude. Using transient transmission and reflection microscopy, we selectively imaged the transport of the carriers near the (001) surface and the bulk carriers in single-crystal MAPbI3 microplates. The surface functionalization increases the diffusion coefficient of the carriers in a 40-nm subsurface region from ~ 0.6 cm2s-1 to ~ 1 cm2s-1, similar to the value for bulk carriers. These results suggest the PEA ligands are effective in suppressing surface defect and phonon scattering and shed light on the mechanisms for enhancing photophysical properties and improving solar cell efficiency.

中文翻译：

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苯乙基铵官能化增强杂化钙钛矿中的近表面载流子扩散

了解半导体表面特性并对其进行化学处理对于提高其在光电器件中的性能至关重要。杂化卤化物钙钛矿已成为一类令人兴奋的高效太阳能材料。然而，它们的器件性能可能会受到阻碍载流子传输和诱导复合的不良表面特性的限制。在这里，我们展示了用苯乙基碘化铵 (PEAI) 对甲基碘化铅 (MAPbI3) 钙钛矿进行表面功能化，PEAI 是二维钙钛矿中常用的间隔阳离子，可以增强近表面区域的载流子扩散，并将缺陷密度降低不止一个数量级。使用瞬态透射和反射显微镜，我们选择性地对 (001) 表面附近的载流子传输和单晶 MAPbI3 微孔板中的大容量载流子的传输进行了成像。表面功能化将 40 nm 次表面区域中载流子的扩散系数从 ~ 0.6 cm2s-1 增加到 ~ 1 cm2s-1，类似于散装载流子的值。这些结果表明 PEA 配体可有效抑制表面缺陷和声子散射，并阐明增强光物理性能和提高太阳能电池效率的机制。