Solution-processed Double Doped PhOLEDs And Its Transient Properties

Solution-processed OLED has always been the high-profile research contents in organic electroluminescence filed.There are many reports about solution-processed OLED based on polymers,in which mature fabricating methods were showed,but the efficiency of these devices were relatively low and stability were also not good enough.However,OLEDs based on small organic molecule owe the properties of relatively high efficiency and better device stability,which make this type OLED the main part of electroluminescence applications in market.This kind of OLED often fabricated by evaporation method because of inferior solubility of small organic molecules,which is bottleneck of big size application.In this thesis,OLEDs based on small organic molecules were fabricated by solution process,different light emitting were realized by multiple doping in emitting layer and the mechanism of device performance change at different operating voltage was discussed.Main content is as follow:(1)Blue PhOLED based on FIrpic with maximum luminance of 3036 cd/m2 was achieved,luminance and current density of OLED increased generally with increasing of FIrpic doping concentration,which illustrated that phosphor material owe good electrical conductivity and the origin of light emitting was generated by direct recombination of charge carriers.And the conclusion that performance of OLEDs using TPBi as host were obviously better than OLEDs with TCTA host,was drawn.In second chapter,Green and Red PhOLEDs were prepared by solution process and their properties were tested.The maximum luminance and current efficiency Green PhOLED based on Ir(ppy)3 were 27580cd/m2 and 33.3cd/A,which was a relative decent result compared with relevant reports.Red device based on Ir(piq)3 exhibited luminance of 5721cd/m2(2)Different light emitting PhOLEDs were obtained by co-doping Ir(ppy)3 and Ir(piq)3 in different weight ratio.The CIE coordinate of these OLEDs could move from(0.31,0.62)to(0.59,0.33).Among these devices,when the weight ratio of TPBi:Ir(ppy)3 was kept at 100:5,there was no light emitting of FIrpic,meanwhile,TPBi's light ratio and device current efficiency decreased as the increasing of FIrpic concentration,we attribute this result to energy transfer process between FIrpic and Ir(ppy)3,which was demonstrated by transient electroluminescence test and the capped charge carriers could affect electroluminescence property substantially.(3)Mechanisms of PhOLEDs based on Ir(ppy)3and Ir(piq)3 double-doping system were researched by transient electroluminescence method,in these OLEDs,light emitting of two materials were independent at some fixed doping ratio.Generally,in electroluminescence device,EL spectra does not change as voltage changing means the main attenuation mechanism of double-doping system PhOLED was "trap effect"caused by material with deep energy level.Ir(ppy)3 own so pretty conductivity that can weaken this "trap effect" and decrease trap concentration,which was demonstrated by transient electroluminescence test.To prove this "trap effect" mechanism,we introduced PTB7,whose energy level is deep,to devices as charge carrier tarp.As it was expected,performance of OLEDs dropped substantially alone with increasing of PTB7doping concentration.In double-doping system type OLED,existence of deep energy level do capture a mass of charge carriers,causing accumulation of charge carriers,probability of interaction between charge and triplets excitons is increased,which cause efficiency roll-off.of this double-doping system type OLED.