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Study On Fabrication Process Of Organic Electroluminescence Device And High Efficiency Phosphorescent OLED Performance

Posted on:2009-02-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:J WangFull Text:PDF
GTID:1118360245461945Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Comparing with LCD,LED or PDP,organic light-emitting diodes(OLED) also named as organic electroluminescence devices(OELD),possess many advantages,e.g., self-emission,fast response,full solid device,easy abrication,high efficiency,wide view-angle,super-thin thickness,and are used as the illumination source and display,. OLED are considered as the most ideal and potential display technology in 21st century. However,the un-consummate fabrication technology causes high device fabrication cost,shorting of high quality emission materials resulte in dissatisfactory device performance,and because of indistinct understanding about mechanism of device, improving about the device shructure and organic materials is uneasy.Aiming at those problems,some creative and systematic works have been performed in this dissert including the key fabrication technology about high resolution device with passive matrix driving method,synthesizing new emission materials to fabricate high efficiency phosphorescent OLED and designing new device structure.1.Indium tin oxide(ITO) thin film used as transparent anode for OLED was deposited on glass substrate with direct current magnetron sputtering system.There are eight parameters affecting the electrical and optical properties of ITO films and orthogonal test table L32(48) was used to carried out the systematic study.Sheet resistance,transmissivity,atomic force microscope,X-ray diffraction and scanning electronic microscope were employed to characterize the ITO films.The optimum parameters for sputtering ITO are:deposition pressure 2 mTorr,flow ratio of argon to oxygen 16:0.5,annealing temperature 427℃,distance between target and substrate 15, annealing time 1 h,sputtering power 300 W,annealing atmosphere pure nitrogen and deposition temperature 127℃.Sheet resistance,transmittance in visible region of the film prepared with above parameters are 17Ω/□and 86.13%,respectively.2.High resolution substrate pattern(1.8inch,128*3*160 pixels) used for passive matrix OLED were fabricated by wet photolithography process.Four photomasks were designed and prepared for chromium(Cr) pattern,ITO pattern,insulator pattem and separator pattern.Cr and ITO pattem recurred on substrate by normal photolithography process(photoresist coating,soft-baking,exposuring,developing,etching,photoresist stripping).Polyimide ZKPI-305 was used as the insulator layer material after high temperature baking process.The separator layer pattern is very hard to achieve by normal process because of its reverse trapeziform shape section.Both negtive photosensitive photoresist(PR) ZKPI530 and positive PR AZ5214 were used for fabricating separator pattern.The pattern can be successfully obtained with AZ5214 using an image reverse technique process,including PR coating,soft-baking,exposing with photomask,reverse baking,flood exposing,and developing.And double separators technology instead of one was used to reduce the difficulty of fabrication process and increase the eligibility rate of separators.3.Line shape evaporation source(line source) can replace the normal dot shape evaporation source(dot source) in the organic material deposition process.The simulation results show that more uniformity thickness of organic thin films and higher utilizable rate of organic material can be obtained with still or relative kinetic line source than dot source.Also an equipment with the line source was designed,which shows some advantages including enhancing the utilizable rate of organic materials, increasing the deposition rate and co-evaporated organic films.4.Novel phosphorescent material(tpbi)2Ir(acac) with green light emission was synthesized and doped in small molecular OLED with the structure ITO/CuPc/NPB/ CBP:(tpbi)2Ir(aeac)/BCP/Alq/LiF:Al.The device shows a maximum luminance of 13500 cd/m2,a maximum power efficiency of 12 lm/W and a current efficiency of 22.9 ed/A.The turn-on voltage of the device is about 4.4 V and the current-voltage characteristic of the device is according with Richardon-Schottky emission model under low voltage.Polymer organic device with the phosphor doped also were fabricated with the structure ITO/PEDOT:PSS/PVK/PFO+30 wt%PBD:(tpbi)2Ir(acac)/Ba:Al.Green light stably emit from the device at different voltages.A maximum luminance of 7841 cd/m2 and current efficiency of 9.95 cd/A were obtained.5.Novel phosphorescent material(t-bt)21r(acac) with yellow light emission was doped in CBP host to achieve small molecular OLED with four organic layers structure. As the driving bias increasing,the current-voltage characteristic of device matches with ohm current transporting,trapped charge limited current(TCLC) and space charge limited current(SCLC) theory,respectively.The device with 5 wt%doping concentration shows a maximum power efficiency of 9.3 lm/W and a luminance of 14360 cd/m2 can be attained by the device with 8 wt%doping concentration.By using ultrathin undoped layer structure,the efficiency of OLED rolls off slowly as the driving voltage increasing.When the phosphor doped in NPB host,the device has a very low turn-on voltage of 2.5 V,and shows a luminance of 100 cd/m2 at 3.25 V,1000 cd/m2 at 4.3 V,10000 cd/m2 at 6.8 V,respectively.Charge carriers directly trapped by the doped phosphor and hole only transporting property are the main reason why the turn-on voltage became lower.6.White light emission organic devices were prepared with the yellow light emission phosphorescent material(t-bt)2Ir(acac) combining with blue light emission fluorescent material NPB.The device with the structure of ITO/NPB/CBP: (t-bt)2Ir(acac)/blue light emission layer/BCP/Alq/LiF:A1,shows a maximum luminance of 7430 cd/m2,a maximum power efficiency of 9.93 lm/W and Commission International de l'Eclairage(CIE) coordinate of(0.34,0.33),which is very near to ideal white point.Using GDI691 as the blue light material instead of NPB,the device shows a max luminance of 15460 cd/m2,and power efficiency of 8.06 lm/W.The coordinates of the device emission locate at white light area of CIE chromaticity diagram under broad driving voltages of 5~12 V,corresponding to the luminance ranging from 167 to 8150 cd/m2.
Keywords/Search Tags:OLED, phosphorescent material, fabrication process, high efficiency, white light
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