Zhao Xi, Lu Haoran, Fang Wei-Hai, Long Run
College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing, 100875, People's Republic of China.
Nanoscale. 2022 Mar 24;14(12):4644-4653. doi: 10.1039/d1nr07732e.
Organic cations are believed to have little influence on the charge carrier lifetime in hybrid organic-inorganic perovskites. Experiments defy this expectation. We consider formamidinium lead iodide (FAPbI) doping with and without Br as two prototypical systems, and perform time-domain nonadiabatic (NA) molecular dynamics simulations to investigate nonradiative electron-hole recombination. The simulations demonstrate that correlated organic-inorganic motion stabilizes the lattice and inhibits nonradiative charge recombination in FAPbI upon Br doping. Br doping suppresses the rotation of FA and the vibrations of both organic and inorganic components, and leads to hole localization and the extent of localization is enhanced upon thermal impact, notably reducing the NA coupling by decreasing the overlap between the electron and hole wave functions. Doping also slightly increases the bandgap for further decreasing NA coupling and enhances the open-circuit voltage of perovskite solar cells. The small NA coupling and large bandgap beat the slow coherence loss, delaying electron-hole recombination and extending the charge carrier lifetime to 1.5 ns in Br-doped FAPbI, which is on the order of 1.1 ns in pristine FAPbI. The obtained time scales are in good agreement with experiments. Multiple phonon modes, including those of both the inorganic and organic components, couple to the electronic subsystem and accommodate the excess electronic energy lost during nonradiative charge recombination. The study reveals the unexpected atomistic mechanisms for the reduction of electron-hole recombination upon Br doping, rationalizes the experiments, and advances our understanding of the excited-state dynamics of perovskite solar cells.
人们认为有机阳离子对有机-无机杂化钙钛矿中电荷载流子的寿命影响很小。然而实验结果却与这一预期相悖。我们将掺杂和未掺杂Br的甲脒碘化铅（FAPbI）视为两个典型体系，并进行时域非绝热（NA）分子动力学模拟，以研究非辐射电子-空穴复合过程。模拟结果表明，相关的有机-无机运动使晶格稳定，并抑制了Br掺杂后FAPbI中的非辐射电荷复合。Br掺杂抑制了FA的旋转以及有机和无机组分的振动，并导致空穴局域化，且热冲击会增强局域化程度，通过减小电子和空穴波函数之间的重叠显著降低了NA耦合。掺杂还略微增加了带隙，进一步降低了NA耦合，并提高了钙钛矿太阳能电池的开路电压。较小的NA耦合和较大的带隙克服了缓慢的相干损耗，延迟了电子-空穴复合，使Br掺杂的FAPbI中电荷载流子寿命延长至1.5 ns，而原始FAPbI中的寿命约为1.1 ns。所得时间尺度与实验结果吻合良好。多种声子模式，包括无机和有机组分的声子模式，都与电子子系统耦合，并容纳了非辐射电荷复合过程中损失的多余电子能量。该研究揭示了Br掺杂后电子-空穴复合减少的意外原子机制，解释了实验结果，并增进了我们对钙钛矿太阳能电池激发态动力学的理解。
