Study On Structure And Performance Of WOLED Based Blue Thermally Activated Delayed Fluorescence

White organic light-emitting diode(WOLED)is widely used in the fields of display and lighting due to the advantages of plane lighting source,flexibility,thinness,and self-luminous.Since the phenomenon of thermally activated delayed fluorescence(TADF)was discovered,TADF materials and TADF exciplexes,without relying on heavy metals,can achieve 100%internal quantum efficiency through the reverse intersystem crossing process in theory.Besides,other advantages,such as broad spectrum and bipolarity,are conducted as emitters or hosts,which contribute to construct WOLED based on TADF materials or exciplexes.At present,single/multiple-emitting-layers structure doped with fluorescent or phosphorescent materials,tandem structure,all-exciplex-based structure and other different structures have been designed in WOLED,but high-performance WOLED still suffers from multi-emitting layers and multi-materials dopping structure currently,which is complex and cumbersome.This paper plans to prepare high-performance blue-orange/red two-colors complementary WOLED with a simple structure based blue TADF by reducing the use of emitters,designing reasonable device structure,utilizing singlet and triplet excitons effectively.And finally to develop the WOLED with low cost,simple structure,high efficiency,low power consumption and high color quality.The main research contents of the paper are as follows:1.Designing a single-layer all fluorescent WOLED based a highly efficient blue TADF as host.The orange-red fluorescent materials,Rubrene and DCJTB,were doped into blue TADF material of m SOAD,respectively.And balanced injection/transport of charge was realized,the leakage of charge/excitons was restricted through reasonable device structure design.After adjusting the doping concentration,a cool white OLED with a correlated color temperature of?7747 K and a maximum external quantum efficiency of 12.2%,a warm white OLED with a correlated color temperature of?3624 K and a maximum external quantum efficiency of 9.0%were obtained,respectively.The triplet excitons are effectively utilized by reverse intersystem crossing on blue TADF material and effective energy transfer between host and guest,which are the main reasons of exceeding 5%external quantum efficiency with simple fluorescent WOLED.2.Preparation of non-doped WOLED based on the combination of blue TADF exciplex and phosphorescent ultra-thin layer.The high-efficiency blue exciplex m CP:PO-T2T was used as the emitting layer,and the ultra-thin Ir(pq)₂accac layer was inserted on both sides,further we studied the influence of the thicknesses of exciplex and ultra-thin layer on the performance.Thickness adjustment can effectively affect the efficiencies and spectra of WOLED:the maximum external quantum efficiency range of variation was 15%?22%,and the correlated color temperature was 1600 K?2600 K.The phosphorescent ultra-thin layer could harvest triplet excitons through charge trapping,which reduced the triplet excitons concentration in exciplex,and weakened the singlet-triplet exciton quenching and triplet-triplet exciton annihilation.Finally,excellent device performances with higher efficiency and lower efficiency roll-off were obtained in non-doped WOLED than doped structure.3.Preparation of two-colors all-exciplex-based WOLED with high color rendering index by combing high-efficiency blue and red exciplex.A high-efficiency red exciplex with a maximum external quantum efficiency of 5.7%was realized by using metal complex of Ir(ppy)₃ as donor and PO-T2T as acceptor.WOLED was designed by using the high-efficiency red exciplex and interface/mixed blue exciplex m CP:PO-T2T,respectively.By changing the thicknesses of donor/acceptor of the interface blue exciplex and the donor/acceptor ratio of mixed blue exciplex,the spectra and efficiencies were easily adjusted,and the optimized devices all had a high color rendering index(>80).In addition,the spacer layer was inserted between the two exciplexes to study the regulation of exciton recombination zone,and further explore the ways of improving spectral stability of WOLED based multi-layer all-exciplex.