Infrared Dielectric Screening Determines the Low Exciton Binding Energy of Metal-Halide Perovskites,The Journal of Physical Chemistry Letters

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Infrared Dielectric Screening Determines the Low Exciton Binding Energy of Metal-Halide Perovskites
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2018-01-22 00:00:00 , DOI: 10.1021/acs.jpclett.7b03286
Paolo Umari _{1,

2} , Edoardo Mosconi _{3,

4} , Filippo De Angelis _{3,

4,

5}

Affiliation

The performance of lead-halide perovskites in optoelectronic devices is due to a unique combination of factors, including highly efficient generation, transport, and collection of photogenerated charge carriers. The mechanism behind efficient charge generation in lead-halide perovskites is still largely unknown. Here, we investigate the factors that influence the exciton binding energy (E_b) in a series of metal-halide perovskites using accurate first-principles calculations based on solution of the Bethe-Salpeter equation, coupled to ab initio molecular dynamics simulations. We find that E_bis strongly modulated by screening from low-energy phonons, which account for a factor ∼2 E_b reduction, while dynamic disorder and rotational motion of the organic cations play a minor role. We calculate E_b = 15 meV for MAPbI₃, in excellent agreement with recent experimental estimates. We then explore how different material combinations (e.g., replacing Pb → Pb:Sn→ Sn; and MA → FA → Cs) may lead to different E_b values and highlight the mechanisms underlying E_b tuning.

中文翻译：

红外介电筛选确定了金属卤化物钙钛矿的低激子结合能

光电器件中卤化钙钛矿的性能归因于多种因素的独特结合，包括高效地产生，传输和收集光生电荷载流子。卤化钙钛矿中有效电荷产生的机制仍然未知。在这里，我们使用基于Bethe-Salpeter方程解的精确的第一性原理计算，以及从头算分子动力学模拟，来研究影响一系列金属卤化物钙钛矿中激子结合能（E _b）的因素。我们发现，通过屏蔽低能声子可以对E _b进行强调制，而低能声子占因子〜2 E _b。还原，而有机阳离子的动态紊乱和旋转运动则起着较小的作用。我们计算出MAPbI _3的E _b = 15 meV，与最近的实验估计非常吻合。然后，我们探讨了不同的材料组合（例如，替换Pb→Pb：Sn→Sn；以及MA→FA→Cs）如何导致不同的E _b值，并重点介绍了E _b调整的基础机制。

更新日期：2018-01-22

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