The Application Of Thermally Activated Delayed Materials In White Organic Light Emitting Diodes

At present,organic light-emitting diodes?OLEDs?technology is changing the people's life as a new generation of display illumination technology.The thermally activated delayed fluorescent?TADF?materials have attracted researchers's wide attention as the third generation of light-emitting material in the OLEDs area.With nearly 20 years of development,many researchers have synthesized TADF materials with excellent performance.Blue,green and red TADF emitters achieved external quantum efficiency?EQE?over 20%already,which can be comparable to phosphorescent emitters.In the field of white organic light-emitting diodes?WOLEDs?,many TADF materials are applied to WOLEDs as emitting materials or assistant dopants to improve device efficiency while a small number of TADF materials can be the host material in OLEDs.The TADF materials which can be used as the host materials in WOLEDs and improve the performance of WOLEDs effectively are still rarely.The research about TADF materials as the host materials in WOLEDs is not systematic enough and the application of TADF materials in WOLEDs should be further studied.In this paper,blue TADF material mSOAD which can achieve high efficiency under non-doped structure is studied and its application in WOLEDs is explored.Firstly,the photoelectric properties of mSOAD were analyzed,and high-performance blue,red and white OLEDs devices were fabricated.Then,TADF materials were used as donors of exciplex,and a high-efficiency pure fluorescent WOLEDs device structure was designed,enlarge the application of TADF materials.Finally,high-performance non-doped WOLEDs were prepared by combining TADF materials with ultra-thin emitter.The specific contents of these studies are as follows:1.In the second chapter,the blue TADF material mSOAD was firstly studied,and the non-doped blue OLEDs were fabricated with a high EQE of14%.Then,the blue TADF material mSOAD and the phosphorescent material Ir?pq?₂acac were used as host and dopant material respectively to manage the excitons.The red OLEDs reach a high maximum current efficiency,power efficiency and EQE of 32.7 cd A^-1,31.0 lm W^-1 and 20.3%,respectively.The WOLEDs with different dopant concentrations exhibit ultra-high color stability and low turn-on voltage.Maximum current efficiencies,power efficiencies and EQEs of WOLEDs with different dopant concentrations are 28.2-32.0 cd A-1,26.3-30.5 lm W-1 and 12.2-17.4%,respectively.2.In the third chapter,we enlarge the application of TADF material mSOAD.mSOAD can be as the donor of exciplex to achieve high efficiency OLEDs.The OLEDs based on mSOAD:PO-T2T exhibits yellow-green emission with high CE,PE and EQE of 31.4 cd A^-1,36.6 lm W^-1 and 9.7%respectively,which also exists a broad spectral coverage of 450-700 nm.After optimized the device structure,the pure fluorescent WOLEDs with CE,PE and EQE of 30.2 cd A^-1,28.0 lm W^-1 and 11.6%respectively are achieved finally.Meantime,stable white emission spectra with CIE coordinates change as low as?0.030,0.008?from 5 V to 8 V are also realized.3.In the fourth chapter,we consider the problems which exists in the previous research.In the host-guest doping system,the doping concentration was difficult to control accurately and the devices repeatability is poor,and the evaporation sources are polluted each other during the preparation.Therefore,the high performance WOLEDs with non-doped structure need to be designed.We combined the blue TADF material mSOAD and red ultrathin emitter for complementary white emitting.The device performances were greatly improved by adjusting the position and quantity of ultrathin layer.The maximum CE,PE and EQE of the best performance WOLEDs are 31.9 cd A^-1,30.4 lm W^-1 and17.3%respectively.At 4-8 V excitation voltage,the CIE value is?0.469±0.008,0.382±0.004?indicating the stable emission of WOLEDs.