Unravelling the Effects of Grain Boundary and Chemical Doping on Electron-Hole Recombination in CH3NH3PbI3 Perovskite by Time-Domain Atomistic Simulation
Unravelling the Effects of Grain Boundary and Chemical Doping on Electron-Hole Recombination in CH3NH3PbI3 Perovskite by Time-Domain Atomistic Simulation
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DOI：
10.1021/jacs.6b00645
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发表时间：
2016-03-23
影响因子：
15
通讯作者：
Prezhdo, Oleg V.
中科院分区：
文献类型：
--
作者：
Long, Run;Liu, Jin;Prezhdo, Oleg V.
推进有机卤化物钙钛矿太阳能电池需要了解载流子动力学。电子空穴复合是一个特别重要的过程，因为它构成了能量和电流损失的主要途径。晶界（GB）在甲基铵碘化铅CH 3 NH3 PbI 3（MAPbI（3））钙钛矿多晶薄膜中是常见的。第一性原理计算表明，GBs对重组的影响很小;然而，实验违背了这一预测。利用非绝热（NA）分子动力学结合时域密度泛函理论，我们表明，GBs显着加速MAPbI（3）中的电子空穴复合。首先，GB通过局部化和贡献于电子和空穴波函数以及通过创建耦合到电子自由度的附加声子模式来增强电子-声子NA耦合。其次，GB降低了MAPbI（3）的带隙，减少了适应电子能量损失所需的振动量子数。第三，声子引起的电子相干性损失基本上保持不变，而不是加速，因为人们可以预期从增加的电子-声子耦合。此外，在GB处用氯取代碘减少了电子空穴复合。通过将最高占据分子轨道（HOMO）密度推离边界，氯将NA耦合恢复到接近原始MAPbI中观察到的值（3）。通过引入高频声子和增加电子能隙的波动，氯缩短了电子相干性。这两个因素成功地竞争。相对于原始的MAPbI（3）减小的带隙，并且有利于长的激发态寿命。模拟结果与实验结果非常吻合，并描述了GBs和氯掺杂剂如何影响钙钛矿太阳能电池中的电子-空穴复合。模拟结果表明，通过合理的GB钝化增加光子到电子的转换效率的路线。
Advancing organohalide perovskite solar cells requires understanding of carrier dynamics. Electron hole recombination is a particularly important process because it constitutes a major pathway of energy and current losses. Grain boundaries (GBs) are common in methylammonium lead iodine CH3NH3PbI3 (MAPbI(3)) perovskite polycrystalline films. First-principles calculations have suggested that GBs have little effect on the recombination; however, experiments defy this prediction. Using nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we show that GBs notably accelerate the electron hole recombination in MAPbI(3). First, GBs enhance the electron-phonon NA coupling by localizing and contributing to the electron and hole wave functions and by creating additional phonon modes that couple to the electronic degrees of freedom. Second, GBs decrease the MAPbI(3) bandgap, reducing the number of vibrational quanta needed to accommodate the electronic energy loss. Third, the phonon-induced loss of electronic coherence remains largely unchanged and not accelerated, as one may expect from increased electron-phonon coupling. Further, replacing iodines by chlorines at GBs reduces the electron hole recombination. By pushing the highest occupied molecular orbital (HOMO) density away from the boundary, chlorines restore the NA coupling close to the value observed in pristine MAPbI(3). By introducing higher-frequency phonons and increasing fluctuation of the electronic gap, chlorines shorten electronic coherence. Both factors compete successfully with. the reduced bandgap relative to pristine MAPbI(3) and favor long excited-state lifetimes. The simulations show excellent agreement with experiment and characterize how GBs and chlorine dopants affect electron-hole recombination in perovskite solar cells. The simulations suggest a route to increased photon-to-electron conversion efficiencies through rational GB passivation.