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

Abstract

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 light-emitting device, which determines the growth of perovskite film directly. In this paper, the perovskite light-emitting diodes (PeLEDs) based on n-type nanocrystalline silicon oxide (n-nc-SiO<sub><i>x</i></sub>: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 than 60%, 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 green-light emission with a maximum current efficiency of 7.93 cd·A<sup>-1</sup> 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.