Wu Yifan, Chu Weibin, Wang Bipeng, Prezhdo Oleg V
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Key Laboratory of Computational Physical Sciences (Ministry of Education), Institute of Computational Physical Sciences, Fudan University, Shanghai 200433, China.
J Am Chem Soc. 2025 Feb 12;147(6):5449-5458. doi: 10.1021/jacs.4c18223. Epub 2025 Jan 29.
The polycrystalline nature of perovskites, stemming from their facile solution-based fabrication, leads to a high density of grain boundaries (GBs) and point defects. However, the impact of GBs on perovskite performance remains uncertain, with contradictory statements found in the literature. We developed a machine learning force field, sampled GB structures on a nanosecond time scale, and performed nonadiabatic (NA) molecular dynamics simulations of charge carrier trapping and recombination in stoichiometric and doped GBs. The simulations reveal long, microsecond carrier lifetimes, approaching experimental data, stemming from charge separation at the GBs and small NA coupling, 0.01-0.1 meV. Stoichiometric GBs exhibit transient trap states, which, however, are not particularly detrimental to the carrier lifetime. Halide dopants form interstitial defects in the bulk, but have a stabilizing influence on the GB structure by passivating undersaturated Pb atoms and reducing the transient trap state formation. On the contrary, excess Pb destabilizes GBs, allowing formation of persistent midgap states that trap charges. Still, the charge carrier lifetime reduces relatively little, because the midgap states decouple from the bands, and charges are more likely to escape back into bands upon a GB structural fluctuation. The atomistic study into the structural dynamics of perovskite GBs and its influence on charge carrier trapping and recombination provides valuable insights into the complex properties of perovskites and the intricate role of GBs in the material performance.
钙钛矿的多晶性质源于其基于溶液的简便制备方法，导致晶界（GBs）和点缺陷的高密度。然而，晶界对钙钛矿性能的影响仍不确定，文献中存在相互矛盾的说法。我们开发了一种机器学习力场，在纳秒时间尺度上对晶界结构进行采样，并对化学计量比和掺杂晶界中的电荷载流子捕获和复合进行了非绝热（NA）分子动力学模拟。模拟结果显示，由于晶界处的电荷分离和较小的NA耦合（0.01 - 0.1 meV），载流子寿命长达微秒，接近实验数据。化学计量比的晶界表现出瞬态陷阱态，然而，这对载流子寿命并非特别有害。卤化物掺杂剂在体相中形成间隙缺陷，但通过钝化不饱和的Pb原子和减少瞬态陷阱态的形成，对晶界结构有稳定作用。相反，过量的Pb会使晶界不稳定，允许形成捕获电荷的持久带隙中间态。尽管如此，电荷载流子寿命的降低相对较小，因为带隙中间态与能带解耦，并且在晶界结构波动时电荷更有可能逃逸回能带。对钙钛矿晶界结构动力学及其对电荷载流子捕获和复合影响的原子尺度研究，为钙钛矿的复杂性质以及晶界在材料性能中的复杂作用提供了有价值的见解。
