Study On The Synthesis And Photoelectric Properties Of Solution-processable Organic Phosphorescent Host Materials And Luminescent Materials

Organic light emitting diodes(OLEDs)have attracted great attention due to their potential in the fields like plat panel disply and illumination.After more than 20 years researches,vacuum-evaporated OLEDs are now matured in terms of materials and device fabrication techniques.However,its complicated manufacturing and high production costs hindered its further developments.Solution processable OLEDs as a novel device fabrication technique,has drawed great intrest among scientific researchers in recent years due to its low-cost for large-scale production and great potential in flexible OLEDs devices,they could be facilely fabricated through spin coating and ink-jet printing,et al.In this dissertation,we designed and synthesized several solution processable materials for OLEDs,including a bipolar host for green phosphorescent emitter,two orange small molecule phosphorescent emitters and a series hyperbranched green phosphorescent copolymer emitters.Finally,we characterized their electroluminescent performance in solution processed phosphorescent organic light emitting diodes(PhOLEDs).(1)A bipolar small molecule host material TF was designed and synthesized by introducing the electron donating indolocarbazole units and electron deficient diphenyl triazine units as the side chain,dibenzothiophene as the nucleus.The as prepared TF host has good solubility in chlorobenzene and good film forming properties and can thus be used in solution processed OLEDs devices.The thermal stability of TF host is satisfying.The thermal decomposition temperature Td(corresponding to the temperature at a weight loss of 5%)is 519 ?,and no obvious glass transition is observed during the endothermic process.In addition,TF has a higher triplet energy ET1=2.72 eV compared with the green phosphor guest IrG ET1=22.55 eV adopted in this work,making sure that the energy could be transferred from the TF host to the IrG guest.Finally,a single-layer OLEDs device was fabricated by doping the IrG guest with a ratio of 4,6 and 8%respectively to the TF host as the emitting layer,and their electroluminescent performances were explored.The best performance was obtained when the IrG doping ratio is 6%,while the maxium current efficiency reaches 16.56 cd A-1.The electroluminescent(EL)spectra of all devices only exhibited the emission from IrG guest at 520 nm with no apparent emission from TF host,indicating that the device structure can achieve complete energy transfer from the TF host to IrG guest.(2)Two orange phosphorescent small molecule emitter IrOl and Ir02 were designed and synthesized by modifying the classical vacuum evaporated type orange phosphorescent emitter Ir(phq)3.The as prepared two emitters have good solubility in chlorobenzene and good film forming properties and can thus be used in solution processed OLEDs devices.By doping IrO1 and IrO2 as the guest in CBP host with various doping ratios as the emissive layer,we prepared the two layer OLEDs devices and studied their electroluminescent performances.Among them,the IrO1 based OLEDs achieved the maximum current efficiency of 45.8 cd A-1 at a doping ratio of 6%,and the corresponding CIE chromaticity coordinates is(0.55,0.45).Such performance is higher than most reported solution-processed orange phosphorescent emitters.In addition,since the side chain of Ir02 is larger than that of IrO1,the IrO2 based device achieved the maximum current efficiency of 27.0 cd A-1 at a higher doping ratio of 8%and the corresponding chromaticity coordinates are(0.59,0.41).(3)With green phosphorescent emitter Ir(ppy)3 as the core,four kinds of solution processable hyperbranched green polymer phosphorescent emitters were designed and synthesized by adjusting the ratio of 2,8-dicyclohexyl-S,S-dioxydibenzothiophene units in the side chain,the four polymers are IrG10,IrG20,IrG30 and IrG40,respectively.On the one hand,by introducing the long alkyl chains to the carbazole unit to increase the solubility of the polymer in organic solvents,we can make them suitable for solution processable OLEDs.On the other hand,by introducing a large hindered cyclohexyl group to the S,S-dioxydibenzothiophene unit,we can ensure to balance the charge carriers of the side chain without reducing the triplet energy of carbazole.Finally,single layer OLEDs were fabricated using these four hyperbranched polymers as the emissive layers and their electroluminescent performances were studied.Among them,the IrG30 based device exhibitted the best performance and can achieve a maximum current efficiency of 13.64 cd A-1,with CIE color coordinates of(0.37,0.60).In the EL spectra,we could only observe the emission from Ir(ppy)3 core at about 520 nm of all devices,without any blue emission from the branch host,indicating that this polymer structure could achieve complete energy transfer from the branch host to the guest core.