Zhang Zhaosheng, Qiao Lu, Mora-Perez Carlos, Long Run, Prezhdo Oleg V
College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875, People's Republic of China.
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
J Chem Phys. 2020 Feb 14;152(6):064707. doi: 10.1063/1.5131342.
Metal halide perovskites constitute a new type of semiconducting materials with long charge carrier lifetimes and efficient light-harvesting. The performance of perovskite solar cells and related devices is limited by nonradiative charge and energy losses, facilitated by defects. Combining nonadiabatic molecular dynamics and time-domain density functional theory, we demonstrate that charge losses depend strongly on the defect chemical state. By considering an extra Pb atom in CHNHPbI, which is a common defect in lead halide perovskites, we investigate its influence on charge trapping and recombination. In a chemically inert form as a Pb interstitial, the extra Pb atom has only a mild influence on charge recombination. However, if the extra Pb atom binds to a native Pb atom to form a dimer, the charge trapping and recombination are greatly accelerated because the Pb-dimer creates a localized midgap trap state that couples strongly to the perovskite valence band edge. Holes disappear from the valence band two orders of magnitude faster than in the pristine perovskite and recombine with conduction band electrons one order of magnitude faster. The simulations identify the phonon modes involved in the nonradiative charge trapping and recombination and highlight the importance of rapid decoherence within the electronic subsystem for long carrier lifetimes. The detailed atomistic analysis of the charge trapping and recombination mechanisms enriches the understanding of defect properties and provides theoretical guidance for improving perovskite performance.
金属卤化物钙钛矿构成了一类新型的半导体材料，具有长电荷载流子寿命和高效的光捕获能力。钙钛矿太阳能电池及相关器件的性能受到由缺陷导致的非辐射电荷和能量损失的限制。结合非绝热分子动力学和时域密度泛函理论，我们证明电荷损失强烈依赖于缺陷的化学状态。通过考虑CHNHPbI中额外的Pb原子（这是卤化铅钙钛矿中常见的缺陷），我们研究了其对电荷俘获和复合的影响。以化学惰性形式作为Pb间隙原子时，额外的Pb原子对电荷复合只有轻微影响。然而，如果额外的Pb原子与一个本征Pb原子结合形成二聚体，电荷俘获和复合会大大加速，因为Pb二聚体产生了一个局域的中间能隙陷阱态，该陷阱态与钙钛矿价带边缘强烈耦合。空穴从价带消失的速度比在原始钙钛矿中快两个数量级，并且与导带电子复合的速度快一个数量级。模拟确定了参与非辐射电荷俘获和复合的声子模式，并突出了电子子系统内快速退相干对长载流子寿命的重要性。对电荷俘获和复合机制的详细原子分析丰富了对缺陷性质的理解，并为提高钙钛矿性能提供了理论指导。
