Research Of OLEDs Based On Thermally Activated Delayed Fluorescence And Thin Film Encapsulation

Organic light-emitting diodes(OLEDs)have aroused much attention in the past thirty years,due to their unique advantages such as self-luminance,low power consumption,wide color gamut and flexibility.Although OLEDs have been commercialized,they still face problems such as low luminous efficiency,short lifetime particularly flexible devices,and high manufacturing cost.In my thesis,I will discuss and explore some means to tackle the above issues,such as developments of new Thermally Activated Delayed Fluorescence(TADF)emitters,high-efficiency white OLEDs and thin film encapsulations.Details are shown as follows:(1)A new TADF emitter,3-(9,9'-Spirobi[fluoren]-6-yl)-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole(SFCC),was developed for blue OLEDs.By introducing fluorene block to the D-A type backbone,which can spread the HOMO distribution resulting in a small ?Est and high PLQY.An OLED device based on SFCC achieved a maximum external quantum efficiency(EQE)of 10.59% and reduced efficiency roll-off,with Commission Internationale de L'Eclairage(CIE)coordinates of(0.17,0.21),which is attributed to the efficient exciton harvesting that occurs through the triplet-to-singlet up-conversion.It significantly surpasses the electroluminescence(EL)performance of the reference emitter 3-Bromo-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole(TRTZ),indicating that the introduction of the 9,9-spiro-bifluorene unit is a promising strategy for the modification of TADF materials.(2)Blue TADF material has higher triplet energy level and excellent EL performance compared with the traditional blue fluorescence materials.A blue TADF material p DCZTZ was doped in Bis-(2-(diphenylphosphino)phenyl)ether oxide(DPEPO)host as a blue emitting layer,and the phosphorescent material iridium(III)bis-(4-phenylthieno[3,2-c]pyridin-ato-N,C2,)acetylacetonate)(PO-01)is doped in the4,4'-N,N'-dica-rbazole-biphenyl(CPB)body as an orange emitting layer.This two-color WOLED has a cascaded energy transfer structure that can maximize the use of the singlet and triplet excitons.The maximum EQE of WOLED is 19.6%,CIE coordinates of(0.40,0.46).It is a standard warm white light.This fluorescence/phosphorescence two-color hybrid WOLEDs using a blue TADF material would be a promising approach to achieve high-efficiency WOLEDs.(3)Thin film encapsulation is the only and the most effective packaging method to prolong the lifetime of for flexible OLEDs.In my thesis,I have investigated different thin film encapsulation methods.Among them,multilayers of UV adhesive and inorganic film are the most effective means to passivate the device against moisture.First,UV adhesive NOA63 was spin coated on OLED and cured in the glove box.Then aluminum oxide(Al2O3)film(20 nm)was deposited on the NOA63 film by atomic layer deposition(ALD).Through the organic/inorganic alternating thin film encapsulation,the device lifetime was enhanced.The lifetime of OLED reached 113.5hours,which is 72% of the OLED encapsulated by rigid glass lip.