基于N型纳米晶硅氧电子注入层的钙钛矿发光二极管

Perovskite light-emitting diodes based on n-type nanocrystalline silicon oxide electron injection layer

钙钛矿材料由于其禁带宽度可调、光致发光量子产率高、色纯高等优点,使得其在发光器件上具有巨大的应用潜力.电子注入材料是钙钛矿发光器件中的重要组成部分,特别是n-i-p型发光器件,其直接影响后面钙钛矿的生长情况.本文通过向钙钛矿发光二极管中引入一种新型电子注入材料,n型纳米晶硅氧(n-ncSiOx:H)借助于n-nc-SiOx:H薄膜平滑的表面,有效地提高了沉积钙钛矿薄膜的结晶质量,同时其能带结构更加匹配,有效地降低了电子的注入势垒.为了进一步提升器件性能,向钙钛矿材料中引入合适比例的甲基溴化胺(MABr)、氯苯反溶剂中引入一定量的苯甲胺(PMA),通过MABr和PMA的协同作用提高了钙钛矿薄膜的覆盖率,降低了钙钛矿薄膜表面的缺陷密度,抑制了钙钛矿薄膜退火过程中的发光猝灭,最终获得了最大电流效率为7.93 cd·A^-1、最大外量子效率为2.13%的n-i-p型钙钛矿发光二极管.

Organometal halide perovskites featuring solution-processable characteristics, high photoluminescence quantum yield(PLQY), and color purity, are an emerging class of semiconductor with considerable potential applications in optoelectronic devices. Electron injection layer is an important component of perovskite lightemitting device, which determines the growth of perovskite film directly. In this paper, the perovskite lightemitting diodes(PeLEDs) based on n-type nanocrystalline silicon oxide(n-nc-SiOx:H) electron injection layer are designed and realized. This novel electron injecting material is prepared by the plasma enhanced chemical vapor deposition(PECVD), and its smooth surface and matched energy band result in superior perovskite crystallinity and low electron injection barrier from the electron injecting layer to the emissive layer,respectively. However, the external quantum efficiency(EQE) of PeLED is as low as 0.43%, which relates to defects and leakage current due to the incomplete surface coverage of perovskite film. The fast exciton emission decay(< 10 ns) stems from strong non-radiative energy transfer to the trap states, and represents a big challenge in fabricating high-efficiency PeLEDs. In order to obtain desirable perovskite film morphology, an excessive proportion of methylammonium bromide(MABr) is incorporated into the perovskite solution, and a volume of benzylamine(PMA) is added into the chlorobenzene antisolvent. The perovskite films suffer low PLQY and short PL lifetime if only MABr or PMA is introduced. When the molar ratio of MABr is higher than60%, the luminescence quenching arising from Joule heating is depressed by employing PMA, contributing to a higher PLQY(> 30%) and a longer carrier lifetime. The synergistic effect of MABr and PMA increase the coverage and reduce the trap density of perovskite film, inhibit the luminescence quenching in the annealing process, and thus facilitating the perovskite film with higher quality. Finally, the n-i-p PeLED exhibits greenlight emission with a maximum current efficiency of 7.93 cd·A^-1 and a maximum EQE up to 2.13% is obtained.These facts provide a novel electron injecting material and a feasible process for implementing the PeLEDs.With further optimizing the perovskite layer and device configuration, the performance of n-i-p type PeLEDs will be improved significantly on the basis of this electron injection material.