White Organic Light-emitting Device And Its Characteristics,

Compared to LED,LCD and PDP,organic light-emitting diodes(OLEDs),also called as organic electroluminescence devices(OELDs) as potential illumination source and display,have many advantages,e.g.,self-emission,fast response,full solid device, easy fabrication,high efficiency,wide view-angle,super-thin thickness.However, currently there are also some shortcomings to prevent it from large scale commercial application such as high fabrication cost,low luminance efficiency and indistinct understanding about device mechanism.Aiming at those problems,in this work,some basic and systematic works have been performed to focus on the fabrication process to obtain high performance device with passive matrix driving method and high efficiency phosphorescent OLEDs.1.First,the background and development of OLEDs were reviewed.Relevant principles about organic electroluminescence were introduced,which is the theoretical basis for the investigation in this study.2.The device of indium-tin-oxide(ITO)/N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1-biphenyl-4,4-diamine(NPB)/2,9-dimenthyl-4,7-diphenyl-1,10-phenanthroline(BCP)/ Mg:Ag with unique simple structure was fabricated.The luminance-voltage and current density-voltage characteristics of devices were investigated.The results demonstrated that the maximum luminance of the double-layer device is 11,500 cd/m² at 15V.The maximum luminous power efficiency is 1.2 lm/W at the luminance of 300 cd/m² and the luminous efficiency of 2.7 cd/A.The peak of electroluminescence(EL) spectrum locates at 433 nm and the Commissions Internationale d'Eclairage(CIE) coordinates are (0.18,0.17),which is consistent with the photoluminescent(PL) spectrum of NPB.The bright blue light emission is independent on the variation of bias voltage.The diversity of device performance with two different structures was discussed.By doping or adjusting the thickness of organic layers,bright high-efficiency WOLEDs can be expected by combining this unique structure with highly fluorescent yellow material.3.Focusing on the mainstream and insufficient development for WOLEDs,three main works of WOLEDs were carded out:(a) phosphorescent material and single-doped emitting layer based WOLEDs,(b) fluorescent material and exciplex emitting layer based WOLEDs,(c) fluorescent material and ultrathin emitting layer based WOLEDs.(a) High-efficiency WOLEDs based on phosphorescent dye bis[2-(4-tert-butylphenyl) benzothiazolato-N,C2']iridium(acetylacetonate)[(t-bt)2Ir(acac)]as yellow emitting layer were fabricated.The turn-on voltage of the device was 3 V with a maximum luminance of 15,460 cd/m² at 16.5 V and a maximum luminance efficiency of 7.5 lm/W at 4 V.The CIE coordinates located at(0.33,0.32) and remained unchanged at over 8 V,almost consistent with optimum the white CIE of(0.33,0.33). The effect of carrier trapping and energy transfer on the device performance was also discussed.(b) With a simple structure of ITO/poly(N-vinylcarbazole)(PVK):NPB/BCP/ Mg:Ag,OLEDs were fabricated by spin coating method.Optimum device performance could be obtained by choosing the concentration proportion of PVK:NPB at 1:1.In EL spectra of the device,except for the emission of NPB,a new peak at 640 nm proposed to be electroplex that formed between PVK and NPB was observed.Also,the relative emission of electroplex increased with enhanced electric field.(c) A high performance undoped white OLED has been fabricated using an ultrathin yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene(rubrene).The rubrene layer was inserted at two sides of interface between two NPB layers,which was as a hole transporting and blue emitting layer,respectively.The results showed that a maximum luminance of the device reached to as high as 21,500 cd/m² at 15 V.Power efficiency at 1000 and 10,000 cd/m² are 2.5 and 1.6 lm/W,respectively.The peaks of EL spectra locate at 429 and 550 nm corresponding to the CIE coordinates of(0.32, 0.33),which is independent on bias voltage.The performance enhancement of the device may result from direct charge carrier trapping and energy transfer mechanism in EL process.This work paved the way for the fabrication of WOLEDs in display technology and high-efficiency light source in processing method and device architecture design.