Department of Chemistry, Yonsei University , Seoul 120-749, Korea.
Department of Mechanical Engineering and Materials Science, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.
ACS Nano. 2017 Mar 28;11(3):3311-3319. doi: 10.1021/acsnano.7b00608. Epub 2017 Mar 13.
Excellent color purity with a tunable band gap renders organic-inorganic halide perovskite highly capable of performing as light-emitting diodes (LEDs). Perovskite nanocrystals show a photoluminescence quantum yield exceeding 90%, which, however, decreases to lower than 20% upon formation of a thin film. The limited photoluminescence quantum yield of a perovskite thin film has been a formidable obstacle for development of highly efficient perovskite LEDs. Here, we report a method for highly luminescent MAPbBr (MA = CHNH) nanocrystals formed in situ in a thin film based on nonstoichiometric adduct and solvent-vacuum drying approaches. Excess MABr with respect to PbBr in precursor solution plays a critical role in inhibiting crystal growth of MAPbBr, thereby forming nanocrystals and creating type I band alignment with core MAPbBr by embedding MAPbBr nanocrystals in the unreacted wider band gap MABr. A solvent-vacuum drying process was developed to preserve nanocrystals in the film, which realizes a fast photoluminescence lifetime of 3.9 ns along with negligible trapping processes. Based on a highly luminescent nanocrystalline MAPbBr thin film, a highly efficient green LED with a maximum external quantum efficiency of 8.21% and a current efficiency of 34.46 cd/A was demonstrated.
具有可调带隙的出色颜色纯度使有机-无机卤化物钙钛矿能够高效地用作发光二极管（LED）。钙钛矿纳米晶体的荧光量子产率超过 90%，然而，在形成薄膜后，其荧光量子产率会降低到低于 20%。钙钛矿薄膜有限的荧光量子产率一直是高效钙钛矿 LED 发展的一个巨大障碍。在此，我们报告了一种在非化学计量加合物和溶剂-真空干燥方法基础上，原位形成具有高光致发光性的 MAPbBr（MA = CHNH）纳米晶体的方法。前驱体溶液中过量的 MABr 相对于 PbBr 对于抑制 MAPbBr 的晶体生长起着关键作用，从而通过在未反应的宽带隙 MABr 中嵌入 MAPbBr 纳米晶体来形成纳米晶体并创建具有 I 型能带排列的结构。开发了一种溶剂-真空干燥工艺来保留薄膜中的纳米晶体，这使得其实现了 3.9 ns 的快速荧光寿命，且不存在明显的俘获过程。基于高度发光的纳米晶 MAPbBr 薄膜，我们展示了一个高效的绿色 LED，其最大外量子效率为 8.21%，电流效率为 34.46 cd/A。
