有机发光材料DPVBi的空穴阻挡特性

讨论了有机发光材料4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl(DPVBi),在结构为ITO/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(NPB)/DPVBi/tris-(8-hydroxyquinoline)aluminum(Alq₃)/LiF/Al的有机电致发光器件中所表现出来的空穴阻挡特性。通过实验可以看到,当NPB的厚度小于DPVBi的厚度时,DPVBi对空穴的阻挡作用和其自身的厚度有关,厚度越大阻挡能力越强。DPVBi的厚度一定(120nm)且不足以将空穴完全限制于DPVBi层内时,其对空穴的阻挡能力,随着NPB厚度(30~60nm)的增加而相对减弱。当NPB的厚度大于DPVBi的厚度时,进入DPVBi层的空穴,随着它们之间厚度差别的增大而增加,从而使器件的光谱半峰全宽加大。这几条规律对于制作基于DPVBi的有机蓝光和有机白光器件具有一定的指导意义。

Hole-blocking Characteristics of Organic Light Emitting Materials DPVBi

The hole-blocking characteristics of organic light emitting materials DPVBi were discussed.The(device) structure included indium tin oxide glass(ITO) substrate/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′diamine(NPB) as hole transparent layer/DPVBi as emitting layer/40 nm tris-8hydroxyquinoline aluminum(Alq₃) as electron transport layer/0.5 nm LiF/100 nm aluminum(Al).Organic materials were deposited by vacuum deposition at 1.33×10^-4 Pa using resistively heated tan-(talum) and quartz boats.The doping was carried out using the co-evaporation method.The layer thickness of the deposited material was monitored in situ using an oscillating quartz thickness monitor.Finally a LiF buffer(layer) and Al cathode were deposited at a background pressure of 1.33×10^-4 Pa onto the organic films.EL spectra and CIE coordination of the devices were measured by PR650 spectra scan spectrometer and the current-voltage-brightness characteristics were simultaneously measured by a Keithley 2400 programmable voltage-current source.All measurements were carried out at room temperature under ambient conditions.The experiment results show that the hole-blocking characteristic is related to the DPVBi thickness and the NPB thickness.While NPB thickness is less than DPVBi thickness,the hole-blocking capacity of DPVBi increases as DPVBi thickness (increases).The hole-blocking capacity of DPVBi decreases as NPB thickness increases when the DPVBi thickness is unchanged(120 nm).While NPB thickness is more than DPVBi thickness,the hole-blocking capacity of DPVBi increases as their thickness difference increases.The hole that through the DPVBi layer into the Alq₃ layer increase,causing the full width at half maximum(FWHM) of the emission spectrum is broaden.In the conclusion,when DPVBi was used to fabricate the organic blue-light device in order to ensure the luminance and efficiency of the device,the exciton in DPVBi layer should be limited,the emission of Alq₃ should be controlled,the FWHM of emission spectra should be decreased,and the chroma of device will be improved.As far as organic white-light device is concerned,the thickness difference between NPB and DPVBi should be controlled when the total thickness of device is less than 100 nm.The method we adopted enables the emissions of each kind of material to achieve equilibrium and the performance of the organic white-light device can be improved obviously.