We study the temporal, spatial, and spectral evolution of charge carriers in hybrid perovskite thin films after optical excitation with a small laser spot. These are conditions typical of microscopy-based studies. After excitation, the spreading of charge carriers in space occurs due to a combination of diffusion, recombination, and photon recycling. To quantitatively understand their relative importance, a numerical model is used to simulate the anticipated photoluminescence (PL) while accounting for these processes. We also experimentally study the evolution of the PL spectrum at different radial positions from the center of the excitation spot. This allows us to extend our previous work on carrier diffusion performed using time-resolved PL microscopy. Our numerical model predicts a position-dependent spectral shift of the waveguided photon energy in agreement with previous reports. However, we show that the spectral shift under our experimental conditions is dominated by band filling. Finally, we study the interplay between pump spot size, diffusion constant, and fluence on carrier transport in the presence of photon recycling. Our results show that in typical micro-PL experiments and modest carrier densities, photon recycling plays a negligible role in enhancing the lateral spreading of carriers.

中文翻译：

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聚焦激发条件下光子回收和能带填充在卤化物钙钛矿光致发光中的作用

我们研究了钙钛矿杂化薄膜中的载流子在用小激光光斑激发后的时间，空间和光谱演化。这些是基于显微镜的研究的典型条件。激发后，由于扩散，复合和光子循环的结合，电荷载流子在空间中发生扩散。为了定量地了解它们的相对重要性，在考虑这些过程的同时，使用数值模型来模拟预期的光致发光（PL）。我们还通过实验研究了从激发点中心到不同径向位置的PL光谱的演变。这使我们能够扩展以前使用时间分辨PL显微镜进行载流子扩散的工作。我们的数值模型与先前的报告一致，预测了波导光子能量的位置相关光谱偏移。但是，我们表明，在我们的实验条件下，光谱位移主要由谱带填充决定。最后，我们研究了在存在光子循环的情况下泵浦光斑大小，扩散常数和对载流子输运的影响之间的相互作用。我们的结果表明，在典型的微型PL实验和适度的载流子密度中，光子循环在增强载流子的横向扩散方面起着微不足道的作用。