Metal halide perovskites with quasi-2D crystal structures have shown excellent electroluminescent properties due to the inherently confined charge diffusion and efficient radiative recombination. But quasi-2D perovskite films can exhibit complex phase characteristics that need to be tailored for achieving high-performance light-emitting diodes (LEDs). Here, we report a unique quasi-2D perovskite thin film structure featuring a 3D perovskite bottom sublayer underneath a mixed 2D–3D perovskite composite upper sublayer, as imaged by low-dose scanning transmission electron microscopy. We demonstrate that the incorporation of a potassium bromide additive can trigger the self-assembly of multiphase perovskite grains toward this bilayer microstructure, probably due to its ability to create heterogeneous nucleation templates for the crystallization of 3D perovskite grains on the precursor–substrate bottom interface. The external quantum efficiency of quasi-2D perovskite LEDs is significantly improved by this bilayer film microstructure. By probing the carrier dynamics using transient absorption spectroscopy, we attribute the LED performance enhancement to the accelerated carrier transfer and recombination across the bilayer film microstructure.

中文翻译：

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自组装双层微结构改进准二维钙钛矿发光二极管

由于固有的受限电荷扩散和有效的辐射复合，具有准二维晶体结构的金属卤化物钙钛矿显示出优异的电致发光性能。但是准二维钙钛矿薄膜可以表现出复杂的相位特性，需要对其进行定制以实现高性能发光二极管 (LED)。在这里，我们报告了一种独特的准二维钙钛矿薄膜结构，其特征是在混合的 2D-3D 钙钛矿复合上亚层下方有一个 3D 钙钛矿底部亚层，如低剂量扫描透射电子显微镜所成像。我们证明掺入溴化钾添加剂可以触发多相钙钛矿晶粒向这种双层微结构的自组装，可能是由于它能够为前驱体-基底底部界面上的 3D 钙钛矿晶粒的结晶创造异质成核模板。这种双层膜微结构显着提高了准二维钙钛矿 LED 的外部量子效率。通过使用瞬态吸收光谱探测载流子动力学，我们将 LED 性能的增强归因于双层薄膜微结构中载流子传输和复合的加速。