Hybrid perovskites exhibit highly efficient optoelectronic properties and find widespread applications in areas such as solar cells, light-emitting diodes, photodetectors, and lasers. Here, we report the innovative synthesis of formamidinium lead iodide (FAPbI₃) single-crystal microsheets via a two-step chemical vapor deposition (CVD) method. The microsheets exhibit hexagonal and trapezoidal shapes, with hexagonal FAPbI₃ growing parallel to the substrate and trapezoidal FAPbI₃ growing perpendicular to the substrate. The dominant role of single-exciton recombination in the photoluminescence (PL) of these microsheets is observed, especially pronounced at low temperatures, attributed to the relatively large exciton binding energies of the samples. Calculations reveal exciton binding energies as high as 110.8 meV for hexagonal and 133.3 meV for trapezoidal FAPbI₃ single-crystal microsheets, attributed to reduced rotational freedom of the formamidinium (FA) ions. Further investigation into low-temperature phase transitions indicates lower transition temperatures (around 100 K) for these microsheets, suggesting reduced FA ion rotational freedom and consequently higher exciton binding energies.

中文翻译：

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两步法化学气相沉积制备具有高激子结合能的 FAPbI3 单晶微片


混合钙钛矿表现出高效的光电特性，广泛应用于太阳能电池、发光二极管、光电探测器和激光器等领域。在这里，我们报道了通过两步化学气相沉积 （CVD） 方法创新合成甲脒碘化铅 （FAPbI₃） 单晶微片。微片呈现六边形和梯形形状，其中六边形 FAPbI₃ 平行于衬底生长，梯形 FAPbI₃ 垂直于衬底生长。观察到单激子复合在这些微片的光致发光 （PL） 中的主导作用，尤其是在低温下，这归因于样品相对较大的激子结合能。计算显示，六边形 FAPbI 3 单晶微片的激子结合能高达 110.8 meV，梯形 FAPbI₃ 微片的激子结合能高达 133.3 meV，这归因于甲脒 （FA） 离子的旋转自由度降低。对低温相变的进一步研究表明，这些微片的转变温度较低（约为 100 K），表明 FA 离子旋转自由度降低，因此激子结合能更高。