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Construction And Optimization Of Spin-Coated Organic Light-Emitting Diodes Based On Thermally-Activated Delayed Fluorescence

Posted on:2019-06-08Degree:MasterType:Thesis
Country:ChinaCandidate:T ZhouFull Text:PDF
GTID:2428330548958686Subject:Organic Chemistry
Abstract/Summary:PDF Full Text Request
Organic light-emitting diodes(OLEDs)have attracted wide attention in the academic world and the industrial world for its superior performance resulted from its active emission nature,massive materials variation,being bendable and so on.After few decades' development,the emitting materials for OLEDs evolved from traditional fluorescence materials,heavy-metal complex phosphorescence materials to present pure organic thermally-activated delayed fluorescence(TADF)materials,and the device structures for OLEDs complicated from simple bilayer structure to trilayer,multiple layers or even tandem structures.So far,the luminance and electro-opto conversion efficiencies of OLEDs had already meet the standard for practical criterion or even the theoretic limit of them.In our daily life,OLEDs are not mysterious anymore.Product ranging from car monitors,electronic viewfinder of cameras,mobile phones,televisions and so on can be seen everywhere.The bottleneck for the further application of OLEDs is the high cost in manufacturing OLEDs.The most widely used method of OLEDs fabrication is vacuum-deposition which consumes too much raw materials,energy and has low yield in fabricating large-size OLEDs.The use of solution process,such as spin-coating and ink printing would pull down the cost.However,the performance of solution-processed OLEDs are lagged behind the vacuum-deposited ones for the lack of appropriate hole transporting material and the difficulty in manufacturing OLEDs with complicated structure to guarantee the device performance.In this thesis,some solutions,such as modifying existed materials,introducing new materials and matching appropriate materials,were brought out for these problems in solution-processed OLEDs and shown good results.In Chapter 1,a brief introduction of the development history,device construction,device fabrication,operation mechanism and the commonly used materials was presented.The advantages and bottleneck of spin-coated OLEDs and promising thermally-activated delayed fluorescence materials were emphasized.In Chapter 2,we aimed at the modification of a commonly used hole injection material,PEDOT:PSS,in solution-processed optoelectronics.The work function of PEDOT:PSS was elevated and the hole-injection barrier from PEDOT:PSS to the emitting layer was decreased through the doping of InCl3 and UV-Ozone treatment.The macroscopical and microcosmic variation after this process was studied through multiple measurements which turned out to be the elimination of PSS and the transformation towards quinoid structure of PEDOT.Spin-coated green TADF OLEDs with this modified PEDOT:PSS achieved a maximum external quantum efficiency of 21.0%which was one of the highest value among the recent works.In Chapter 3,the recently widely studied organic-inorganic hybrid perovskite(OIHP)was introduced as the hole transporting material in spin-coated TADF OLEDs to solve the lack of appropriate hole transporting materials for solution-processed OLEDs.We designed a carbazole modified two dimensional OIHP,CzEAP,to match the relatively low charge mobilities in OLEDs.The fabrication of CzEAP could perfectly integrate into the spin-coated OLEDs without corrupting the former or later layers and prevent exciton dissociation of TADF emitting layer,boost reverse intersystem crossing.Spin-coated green TADF OLEDs with CzEAP achieved a maximum external quantum yield of 15.3%which was 76%higher than that of a reference device without it.In Chapter 4,several blue and orange TADF emitters were examined to fabricate spin-coated single emitting layer TADF WOLEDs aiming at the problem that it is hard to fabricate solution-processed multiple emitting layer OLEDs.The influence of the matching between the lifetime of the blue and orange TADF emitters'delayed fluorescence to the performance of OLEDs were studied.The energy transfer process and rates between the blue and orange TADF emitters were studied and calculated from transient fluorescence spectra and so on.Finally,spin-coated single emitting layer TADF WOLEDs based on DMAc-DPS-Cz and ClPPM achieved a maximum external quantum efficiency of 23.3%which was one of the highest efficiency among the recent works.
Keywords/Search Tags:thermally-activated delayed fluorescence, spin-coated organic light-emitting diodes, hole injection materials, white organic light-emitting diodes
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