Zhu Zhaohua, Li Yang, Guan Zhiqiang, Wu Yan, Zeng Zixin, Tsang Sai-Wing, Liu Shihao, Huang Xiao, Lee Chun-Sing
Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong SAR 000000, P. R. China.
Department of Chemistry, City University of Hong Kong, Kowloon 000000, Hong Kong SAR, P. R. China.
ACS Appl Mater Interfaces. 2023 Feb 8;15(5):7044-7052. doi: 10.1021/acsami.2c19230. Epub 2023 Jan 27.
Perovskites show efficient electroluminescence and are expected to have wide applications in light-emitting diodes (LEDs). However, owing to the unbalanced electron-hole transport properties of some highly luminescent perovskites, a fundamental challenge is that the exciton recombination zone of perovskite LEDs (PeLEDs) typically overlaps with an accumulation of the major carrier. It is known to reduce the performances of PeLEDs, leading to a reduction of efficiency and operation stability due to Auger recombination. To address this issue in a hole-dominated blue PeLED, we propose to insert a cesium acetate (CsAc) layer between the hole transport layer (HTL) and the hole-dominant perovskite layer. Electronic properties indicate that the hole accumulation zone of the device with the CsAc layer shifts away from the perovskite/ETL interface, i.e., the recombination zone, to the HTL/CsAc interface. Separation of the hole accumulation region and the exciton recombination zones substantially suppresses exciton quenching. Moreover, the CsAc layer can also improve the photophysical properties of the perovskite film by providing an extra Cs source to interact with the defect site of unreacted PbBr in the perovskite film and enhance the crystallinity of the perovskite with an enlarged crystal grain size. As a result, the external quantum efficiency (EQE) of the sky-blue PeLEDs shows considerable improvement from 5.3 to 9.2% upon inserting the CsAc layer.
钙钛矿具有高效的电致发光特性，有望在发光二极管（LED）中得到广泛应用。然而，由于一些高发光性钙钛矿的电子-空穴传输特性不平衡，一个基本挑战是钙钛矿发光二极管（PeLED）的激子复合区通常与主要载流子的积累区重叠。众所周知，这会降低PeLED的性能，由于俄歇复合导致效率和运行稳定性降低。为了解决空穴主导的蓝色PeLED中的这个问题，我们建议在空穴传输层（HTL）和空穴主导的钙钛矿层之间插入一层醋酸铯（CsAc）。电子特性表明，具有CsAc层的器件的空穴积累区从钙钛矿/电子传输层（ETL）界面，即复合区，转移到了HTL/CsAc界面。空穴积累区和激子复合区的分离显著抑制了激子猝灭。此外，CsAc层还可以通过提供额外的Cs源与钙钛矿薄膜中未反应的PbBr的缺陷位点相互作用，并通过增大晶粒尺寸来提高钙钛矿的结晶度，从而改善钙钛矿薄膜的光物理性质。结果，插入CsAc层后，天蓝色PeLED的外量子效率（EQE）从5.3%显著提高到了9.2%。
