Band gap tunability of lead mixed halide perovskites makes them promising candidates for various applications in optoelectronics. Here we use the localization landscape theory to reveal that the static disorder due to iodide:bromide compositional alloying contributes at most 3 meV to the Urbach energy. Our modeling reveals that the reason for this small contribution is due to the small effective masses in perovskites, resulting in a natural length scale of around 20 nm for the “effective confining potential” for electrons and holes, with short-range potential fluctuations smoothed out. The increase in Urbach energy across the compositional range agrees well with our optical absorption measurements. We model systems of sizes up to 80 nm in three dimensions, allowing us to accurately reproduce the experimentally observed absorption spectra of perovskites with halide segregation. Our results suggest that we should look beyond static contribution and focus on the dynamic temperature dependent contribution to the Urbach energy.

中文翻译：

---

混合卤化物钙钛矿的电子无序景观

铅混合卤化物钙钛矿的带隙可调性使其成为光电领域各种应用的有前途的候选者。在这里，我们使用局域化景观理论来揭示由于碘化物：溴化物成分合金化引起的静态无序对 Urbach 能量的贡献最多为 3 meV。我们的模型表明，这种小贡献的原因是钙钛矿中的有效质量小，导致电子和空穴的“有效限制电势”的自然长度尺度约为 20 nm，短程电势波动得到平滑. Urbach 能量在整个组成范围内的增加与我们的光吸收测量结果非常吻合。我们在三个维度上对尺寸高达 80 nm 的系统进行建模，使我们能够准确地再现实验观察到的具有卤化物偏析的钙钛矿的吸收光谱。我们的结果表明，我们应该超越静态贡献，关注动态温度对 Urbach 能量的依赖贡献。