Enhanced performance of organic/inorganic hybrid perovskite light emitting diodes by facile treatment

Abstract

Recently, various types of luminous materials have been studied as candidate materials for next-generation displays. Especially, organic/inorganic hybrid perovskite materials are one of the promising materials for next generation displays. Organic/inorganic hybrid perovskite material have strong points such as high color purity, high charge carrier mobility and scalable soluble processing at low temperature. However, most of researches are focusing on green light emitting materials such as CH3NH3PbBr3 (MAPbBr3) or NH2CHNH2PbBr3 (FAPbBr3) etc. Therefore, it is important to develop perovskite materials which can emit different colors, especially shorter wavelength lights. In this thesis, I have suggested new ways to overcome the limitations of perovskite materials that can emitting shorter wavelength light than perovskite materials that has been widely studied. Here, a new protocol for fabricating a stable perovskite nanocrystal layer with tunable bandgap via simple nanocrystal pinning process was introduced. The perovskite nanocrystals were composed of MAPbBr3 mixed with (vinylbenzylamine)2PbBr4 ((VBzA)2PbBr4) which contains a photopolymerizable structure-directing ligand. With the increasing amount of (VBzA)2PbBr4, the bandgap continuously increased by reduction of the nanocrystal size and also lattice distortion. The nanocrystal film was readily polymerized upon exposure to visible light and stable in humid air more than 15 days. Its application as bluish green light emitting diodes is demonstrated. Furthermore, we introduced post treated electrical field annealing of perovskite materials. Since the electrical field which is applied to perovskite materials can induce ion migration in perovskite crystals, the crystallinity of perovskite materials can be enhanced. Additionally, to induce recrystallization of perovskite materials, heat and electrical field should be applied simultaneously. Also, MAPbBr3 PeLEDs showed better performance when the electrical field annealing is applied. With MAPbBr3 based PeLEDs, electrical field annealed sample showed 1.5 times and 2 times higher maximum luminance and current efficiency respectively. Furthermore, for quasi-2D perovskite based PeLEDs, electrical field annealed sample showed much enhanced current flow. This leads much higher luminance, otherwise it does not show any light emitting. Also after electric field annealing, EL spectrum has been shifted around 4 nm. Based on this phenomenon, while electrical field is applied, recrystallization of perovskite crystals are happen.