Organic Light Emitting Diodes With Solution-Processed Organic-Inorganic Metal Halide Perovskite As Host Materials And Their Luminescence Mechanisms

Organic light emitting diodes?OLEDs?have been widely studied due to their advantages of ultra-thin thickness,flexibility and fast response speed.Efficient OLEDs typically use organic host materials,which suffer from low and unbalanced carrier mobilities.Organic-inorganic hybrid perovskite materials,with high carrier mobility and balanced bipolar carrier transport,are potential candidates as solution-processed host materials for OLEDs.In this thesis,MAPb Br₃?MA=CH₃NH₃?was used as the host material for the luminescent guests including phosphorescent organic molecules and thermally activated delayed fluorescent materials.For the first time,a new perovskite-organic host-guest composite emitting layer prepared by solution processing was reported.The main works are as folloes below.Firstly,the phosphorescent organic small molecule,bis?1-phenyl-isoquinoline-C2,N??acetylacetonato?iridium?III??Ir?piq?₂acac?,was selected as the luminescent guest.The MAPb Br₃:Ir?piq?₂acac composite emitting layer was prepared by the simple solution processing.The experimental results show that Ir?piq?₂acac mixing has no effect on the energy level structure and crystal structure of MAPb Br₃,but the grain size of MAPb Br₃is reduced from 85 nm to 43 nm.The thickness of the composite emitting layer is about110 nm.Energy transfer and charge transfer from MAPb Br₃ to Ir?piq?₂acac contribute to the luminescence process.By optimizing the preparation method,doping concentration and film thickness,the best device performance with a maximum luminance of 742 cd/m²?@8 V?,a maximum current efficiency of 0.17 cd/A?@5 V?and a turn-on voltage of3.1 V are achieved.The study on the interaction and the mechanism of perovskite and organic materials has proved the potential of MAPb Br₃ as the host material for OLEDs,also provide guidance and reference for the impact of perovskite-organic systems in other fields.Secondy,the thermally activated delayed fluorescent material,2-[4-?diphenylamino?phenyl]-10,10-dioxide-9H-thioxanthen-9-one?TXO-TPA?,was selected as the guest material for the OLEDs based on MAPb Br₃:TXO-TPA composite emitting layer.The experimental results show that TXO-TPA with a concentration of 16 mg/ml in toluene solution enables effective energy transfer and charge transfer from MAPb Br₃ to TXO-TPA.The best performance of the devices shows a maximum current efficiency of 0.8cd/A,a maximum luminance of 220 cd/m²and a turn on voltage of 6.4 V.Moreover,1,3,5-tris?1-phenyl-1H-benzimidazol-2-yl?benzene?TPBi?was inserted between the hole transport layer and the emitting layer as the electron blocking material.The injection current density of the devices is effectively improved and electrons are confined efficiently in emitting layer with the TPBi thickness of 4 nm.The turn-on voltage of the device is reduced from 11.4 V to 10.4V and the current efficiency is increased to 0.18cd/A.This research provides an effective solution for improving the performance of OLEDs based on perovskite host materials.