Study On Preparation And Properties Of OLED Carrier Transport Materials

In recent years,the OLEDs(Organic Light Emitting Diodes)industry have developed rapidly,and have been widely applied in the screen display field and the lighting field.However,due to the high cost and difficult manufacturing process of the vacuum evaporation method,the application and development of the vacuum evaporation method were limited.In order to further save the cost and difficulty of device production,researchers have developed a more convenient and less costly device production method?solution method.Although the interlayer miscibility problems exist in the fabrication process of the solution method,the solution method is widely used due to its low consumables,low cost and simple operation.Therefore,it is worth exploring how to make use of the strengths and avoid weaknesses to produce low-cost and high-performance devices.Using the cross-linking techniques can effectively reduce the interlayer miscibility problems,it is to graft the photocrosslinkable or thermally crosslinkable functional group onto the organic carrier transport materials and to transform them into the crosslinkable carrier materials.When the crosslinkable carrier materials are used for OLED devices,the crosslinkable carrier materials will be converted from small molecular materials to polymer materials by heating or light,so as to achieve the effect of anti-solvent and effectively avoid the interlayer miscibility problems.This thesis mainly synthesized a variety of carrier transport materials with cross-linking functional groups,and further tested their properties.The main work content can be divided into the following four parts:In the first part,using oxadiazole as the classic carrier transport unit and styrene as the thermal cross-linking functional group,a double-branched and a three-branched thermally cross-linkable electron transport materials are prepared,named D-OXD and T-OXD.The emission peaks of the two compounds were at 386 nm and 366 nm,respectively.Differential Scanning Calorimetry(DSC)of the compounds showed that the cross-linking temperature was at 180?,and their solvent resistances were further tested.Their crosslinking conditions were annealing at 180? for 1 h and 170? for 1 h,respectively.The HOMO energy levels of the molecules were-5.45 and-5.65eV,the LUMO energy levels were-2.04 and-2.09eV,and their optical bandgaps were 3.41 and 3.56eV,respectively.The results showed that as the number of cross-linking functional groups increased,the solvent resistance of the film was correspondingly enhanced after cross-linking.In the scend part,using oxadiazole as the electron transport unit,and oxetane and butene as cross-linking functional groups,and terphenyl was used as the core to enhance the molecular conjugation,and the solubility of the compound was reinforced with a longer carbon chain,two compounds(Ox-OXD and Bu-OXD)had been synthesized.The emission of the two compounds were tested at 380 nm.The HOMO and LUMO energy levels of the compounds were-5.05/-1.55eV and-5.12/-1.62eV,respectively,and their optical bandgaps were 3.51eV.The decomposition temperatures(5%weight loss)were 320? and 200?,respectively.In the third part,based on the second part,taking into account the problem of molecular solubility and a more reasonable molecular structure,a four-branched hole transport material with thermally crosslinked styrene groups was prepared,in which two diphenylamines were attached to both ends of a 2,2?-binaphthalene skeleton,and named as Na-St.The fluorescence emission of the compound was tested at 473 nm.The HOMO and LUMO energy levels was-5.37/-2.53eV,and the optical bandgap was-2.84eV.DSC showed that the crosslinking temperature of the compound was 150?,and the anti-solvent performance of the compound reached 100%by thermal curing at 200? for 1h.In the fourth part,based on the third part,triphenylamine was selected as the hole transport material,and cyclohexane was used as the carbon chain to enhance the solvent properties of the compounds,two hole transport materials with thermally crosslinked groups were designed and synthesized,and named TAPC-V and TAPC-S respectively.After testing,the fluorescence emission peaks of these two compounds were both at 424 nm.The HOMO and LUMO energy levels were-5.43/-5.28eV and-2.18/-2.03eV,and their optical bandgaps were 3.25eV.DSC showed that the cross-linking temperature were 150 and 215?,respectively.After anti-solvent testing,the crosslinking conditions of the two compounds were annealing at 160? for 1 h and annealing at 190? for 1 h.These two materials were used as hole transport materials to prepare OLED devices(ITO/HATCN(15 nm)/TAPC-V(30nm)or TAPC-S(30 nm)/CBP:Ir(mppy)₃(30 nm)/TPBI(35 nm)/Liq(2 nm)/Al(150 nm))with high efficiency,EQE of the devices were greater than 15%.