Obtaining insight into, and ultimately control over, electronic doping of halide perovskites may improve tuning of their remarkable optoelectronic properties, reflected in what appear to be low defect densities and as expressed in various charge transport and optical parameters. Doping is important for charge transport because it determines the electrical field within the semiconducting photoabsorber, which strongly affects collection efficiency of photogenerated charges. Here we report on intrinsic doping of methylammonium lead tri-iodide, MAPbI₃, as thin films of the types used for solar cells and LEDs, by I₂ vapor at a level that does not affect the optical absorption and leads to a small (<20 meV, ∼9 nm) red shift in the photoluminescence peak. This I₂ vapor treatment makes the films 10× more electronically conductive in the dark. We show that this change is due to p-type doping because we find their work function to increase by 150 mV with respect to the ionization energy (valence band maximum), which does not change upon I₂ exposure. The majority carrier (hole) diffusion length increases upon doping, making the material less ambipolar. Our results are well-explained by I₂ exposure decreasing the density of donor defects, likely iodide vacancies (V_I) or defect complexes, containing V_I. Invoking iodide interstitials, which are acceptor defects, seems less likely based on calculations of the formation energies of such defects and is in agreement with a recent report on pressed pellets.

中文翻译：

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I ₂进行MAPbI ₃ p掺杂的机理是什么？光电特性的见解

深入了解并最终控制卤化钙钛矿的电子掺杂，可能会改善其显着的光电性能的调整，这反映在缺陷密度低的情况下，并以各种电荷传输和光学参数表示。掺杂对于电荷传输很重要，因为它决定了半导体光吸收剂内的电场，这会严重影响光生电荷的收集效率。在这里，我们报道了I ₂蒸气对甲基碘化三碘化铅MAPbI ₃作为用于太阳能电池和LED的薄膜类型的内在掺杂，其掺杂水平不会影响光吸收，并且会导致少量（< 20 meV，〜9 nm）在光致发光峰中发生红移。这个我₂蒸汽处理使薄膜在黑暗中的导电性提高了10倍。我们显示出这种变化是由于p型掺杂引起的，因为我们发现它们的功函数相对于电离能（价带最大值）增加了150 mV，而在I ₂暴露时不变。掺杂时多数载流子（空穴）的扩散长度增加，从而使材料的双极性降低。I ₂暴露可降低供体缺陷的密度，可能的碘化物空位（V _I）或包含V _I的缺陷复合物的密度，这可以很好地解释我们的结果。。基于对这些缺陷的形成能的计算，作为受体缺陷的碘化物间质的调用似乎不太可能，并且与关于压制小球的最新报道是一致的。