Understanding carrier relaxation in lead halide perovskites at the nanoscale is critical for advancing their device physics. Here, we directly image carrier cooling in polycrystalline CH₃NH₃PbI₃ films with nanometer spatial resolution. We observe that upon photon absorption, highly energetic carriers rapidly thermalize with the lattice at different rates across the film. The initial carrier temperatures vary by many multiples of the lattice temperature across hundreds of nanometers, a factor that cannot be accounted for by excess photon energy above the bandgap alone or in variations of the initial carrier density. Electron microscopy suggests that morphology plays a critical role in determining the initial carrier temperature and that carriers in small crystal domains decay slower than those in large crystal domains. Our results demonstrate that local disorder dominates the observed carrier behavior, highlighting the importance of making local rather than averaged measurements in these materials.

中文翻译：

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金属卤化物钙钛矿薄膜中载流子冷却的超快成像

了解纳米级卤化钙钛矿中载流子的弛豫对于提高其器件物理性能至关重要。在这里，我们直接对多晶CH ₃ NH ₃ PbI _3中的载流子冷却进行成像具有纳米空间分辨率的胶片。我们观察到，在吸收光子后，高能载流子会以不同的速率在整个薄膜上迅速地与晶格热化。初始载流子温度跨数百纳米变化，是晶格温度的许多倍，这不能由单独的带隙之上的过量光子能量或初始载流子密度的变化来解释。电子显微镜表明，形态在确定初始载流子温度中起关键作用，并且小晶畴中的载流子衰变慢于大晶畴中的载流子。我们的结果表明，局部紊乱主导了观察到的携带者行为，突出了在这些材料中进行局部测量而不是平均测量的重要性。