Preparation And Electroluminescent Property Of Zinc Bis (2-substituted-8-hydroxy Quinolatos) And Their Organic Light-emitting Devices

The technique of organic light-emitting devices(OLEDs)attracts world wide attention in the fields of science and industry due to its outstanding advantages including light weight,low power consumption,wide viewing angle,high response speed,spontaneous light-emitting,high brightness and efficiency,etc.It has become an interdisciplinary research and the focus of international competition especially in recent over ten years since C.W.Tang and his co-workers reported the high brightness OLED at low operating voltage for the first time in 1987.Although much progress has been achieved on OLEDs,further study on novel material,device structure,process technologies and luminescence mechanism in order to improve the performance of OLEDs is still the research focus in the world.Metal complex is considered as the most promising emitting material because of its high fluorescence and stability.Inspired by the successful application of AlQ₃ (tris(8-quilnolinolato)aluminum)in OLEDs,scientists desire to explore new materials just as good,may be even better than AlQ₃.This dissertation focuses on synthesizing new zinc complexes by chemically modifying alkyl or aryl-quinolate in the 2-position of ligand and designing novel OLED structure in order to enrich luminescent colors and improve the electroluminescent properties.Of course,we discuss the electroluminescent mechanism at the same time.The details are given as follows:Chap 1:IntroductionRecent developments in the study on the organic light-emitting display are presented.Chap 2:Synthesis and characterization of zinc 2-alkyl or aryl-quinolate Five 2-substituted-8-hydroxyquinoline compounds and their zinc complexes were synthesized and characterized by ¹H-NMR,MS,UV-Vis and fluorescent spectroscopy.Here we reported the first use of PC instead of toxic,volatile organic solvent as media solvent towards metal salts for electrochemically determining HOMO,LUMO and energy gap of these new series of zinc compounds.The result agreed with UV-Vis absorption spectroscopy and quantum chemical calculation.The relation between the emissive property and the substituent in the 2-position of the quinoline ring was discussed on the basis of experiment and theory calculation.Chap 3:Fabrication and electroluminescence property of zinc complexes-based OLEDThe organic light-emitting devices with the structure of ITO/TPD(N, N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine)/zinc quinolates/ AlQ₃/Al were further fabricated.The electroluminescent peaks ranged from 540nm to 561nm,and colors changed from yellowish green to yellow due to the substitution effect.In addition,the photoelectric property comparison of OLED between zinc complex and AlQ₃ was carried out.The results showed all zinc quinolates-based devices had lower operating voltage and higher brightness.It is therefore predicted that these zinc complexes can be considered as excellent emitting materials for OLED in the future.Chap 4:Fabrication and characterization of a novel white OLED based on hole blocking lay BCPA white organic light-emitting devices with a structure of ITO/NPB(N,N'-Di-[(1-naphthalenyl)-N,N'-diphenyl]-(1,1'-biphenyl)-4,4'-diamine)/B CP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)/Zn(Q-4-biPh)₂/Al was obtained and studied.The mixture light from double emitting materials of NPB(blue-light emission)and Zn(Q-4-biPh)₂(yellow-light emission)was achieved by effectively adjusting the thickness of BCP which functioned as hole blocking layer.When a 2.0 nm-thick BCP was used,white-light emission was obtained.With a lower turn-on voltage at about 6 V,the white OLED showed a maximum brightness of 130 cd/m² and current efficiency of 0.224 cd/A at 20 V.Chap 5:Fabrication and characterization of OLED with RhB doped in ZnQ₂By vacuum evaporation deposition,dye-doped OLEDs were fabricated with the structure of ITO/TPD/ZnQ₂:Rhodamine B(RhB)/Al.The luminescent layer was composed of a dye RhB doped into ZnQ₂(bis(8-hydroxyquinolato)zinc)layer which showed much better electroluminescent properties than AlQ₃(tri(8-hydroxyquinolato) aluminum).With different RhB concentration,OLED electroluminescence emission got different peak wavelength and visual color.The maximal shift of 34nm was obtained due to dopant concentration.The emission wavelength and intensity can be also tuned by varying the applied voltage.By investigating photoluminescent as well as electroluminescent behaviors,the energy transfer mode and emission mechanism were discussed in this paper.Both energy transfer and carrier trapping have been suggested to be responsible for dopant excitation and emission.Chap 6:Efficient energy transfer by introducing Zn(Q-4-biPh)₂ as assistant in a DCJTB-doped OLEDIn order to obtain a complete energy transfer from host to guest in OLEDs, Zn(Q-4-biPh)₂ was.used to assist the energy transfer from NPB to the red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB).The efficient emission of DCJTB was achieved via above-mentioned cascade energy transfer from NPB to Zn(Q-4-biPh)₂ and then to DCJTB.OLEDs' structure was ITO/NPB(10nm)/NPB:DCJTB(30nm)/BCP(xnm)/Zn(Q-4-biPh)₂(30nm) /Al,where BCP not only functioned as hole blocking layer,but also controlled energy transfer proportion from Zn(Q-4-biPh)₂ to DCJTB.Chap 7:Fabrication and electroluminescence of a non-doping OLED based on Zn(Q-Ph)₂ and DCJTBDCJTB and Zn(Q-Ph)₂ were used to fabricate a novel kind of non-doping OLED with a structure of ITO/NPB(30nm)/DCJTB(xnm)/Zn(Q-Ph)₂(40 nm)/AlQ₃(30 nm)/Al(200 nm).By varying the thickness of ultra-thin layer DCJTB,its luminescent color,electroluminescent mechanism and recombination zone were optimized in this paper.When a 0.5 nm-thick DCJTB was used,a stable red emission was obtained. With a lower turn-on voltage at about 5.5 V,the non-doping OLED showed a maximum brightness of 420 cd/m² and current density of 250 mA/cm² at 25 V.Chap 8:An investigation on a novel PDLC Film's fabrication and its electro-optical properties A polymer dispersed liquid crystal(PDLC)film that has good electro-optical properties is produced by the method of polymerized-induced phase separation.Based on the application foreground,its capability parameters such as contrast ratio,work voltage and visual angle are characterized for the first time by a white light but not a fixed wavelength light.The results show the PDLC film has a low work-voltage of 20V,more than 150-degree visual angle,high stability and long lifetime.The differences between plastic and glass ITO-coated substrates of PDLC films are also studied in this paper.The plastic substrate has better property and will have a wider perspective especially in the portable,tender and folded display devices.Due to adjustable properties of film by electric field,PDLC has the potential application for display device,sensor,switch,grating and new generation analytical apparatus.