Phonon scattering with photogenerated excitons and free charges greatly affects optoelectronic properties of metal halide perovskites and governs their emission line width. Benefiting from the improved phase purity, we are able to analyze exciton–phonon coupling in 2D and quasi-2D BA₂MA_n–1Pb_nI_3n+1 (n = 1–3) thin films using temperature-dependent photoluminescence (PL) spectroscopy. The layer thickness (n value) dependent coupling of free excitons with both acoustic and longitudinal optical (LO) phonons was extracted quantitatively by fitting the temperature-dependent PL line width and band gap. The low energy emissive signatures below free excitons at low temperature might belong to the emission of self-trapped excitons and bounded excitons in structural defects. Our findings provide a systematic picture for the layer thickness (n value) dependent exciton–phonon coupling in 2D and quasi-2D perovskite thin films and could be helpful for improving the optoelectronic performance of devices made by Ruddlesden–Popper perovskite thin films.

中文翻译：

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具有改进的相纯度的二维和准二维 BA2MAn–1PbnI3n+1 薄膜中的激子-声子耦合和低能量发射

具有光生激子和自由电荷的声子散射极大地影响了金属卤化物钙钛矿的光电特性并控制了它们的发射线宽度。受益于提高的相纯度，我们能够使用温度相关的光致发光分析二维和准二维 BA ₂ MA _{n –1} Pb _n I _{3 n +1} ( n = 1–3) 薄膜中的激子-声子耦合（ PL) 光谱。层厚 ( n通过拟合温度相关的 PL 线宽和带隙，定量提取自由激子与声学和纵向光学 (LO) 声子的依赖耦合。低温下自由激子以下的低能量发射特征可能属于结构缺陷中自陷激子和有界激子的发射。我们的研究结果为2D 和准 2D 钙钛矿薄膜中层厚度（n值）依赖的激子-声子耦合提供了系统图，并且可能有助于提高由 Ruddlesden-Popper 钙钛矿薄膜制成的器件的光电性能。