Ultra-thin Layers And DCM-Type Red-Light-Emitting Materials For Electroluminescence Applications

Fristly we investigated the effect of LiF ultra-thin layer on the performance of OLEDs. (1) We enhanced the efficiency and luminance of the OLEDs by inserting a LiF ultra-thin layer between NPB (N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1'-biphenyl-4,4'-diamine) and Alq₃ (tris(8-quinolinolato) aluminum). A 0.3nm LiF ultra-thin layer shows the optimal effects and explained based on tunneling theory. The device with two LiF ultra-thin layers both at the organic-organic interface and at the cathode-organic interface respectively showed the highest luminance of 23000cd m^-2 at a fixed bias of 20V. (2) A novel OLEDs was fabricated by inserting a ultra-thin LiF layer in emitting layer (Alq₃). The electroluminescence device showed expanded Electroluminescence (EL) spectra. The spectra contain tricolor, so this is a simple method to realize white light emitting.Secondly we designed and synthesized three new starburst DCM (4-(dicyanomethylene)-2-methyl-6- [4-(dimethylaminostyryl)-4H-pyran]) derivatives, 4,4',4"-tris[2-(4-dicyanomethylene-6-t-butyl-4H-pyran-2-yl)-ethylene]triphenylamine (TDCM), 4,4',"-tris[2-(4-(1',3'-indandione)-6-t-butyl-4H-pyran-2-yl)-ethylene] triphen-ylamine (TIN), and 4-methoxy-4',4"-bis[2-(4-(1',3'-indandione)-6-t-butyl-4H-pyran-2-yl)-ethylene] triphenylamine (MBIN) for application as red-light emitters in OLEDs. They emit more efficiently than DCM1 (4-(dicyanomethylene)-2-methyl-6-[p-(N,N-dimethylamino)-styryl]-4H-pyran) in EL devices, as evidenced by the L_max ratio of 1:1.3:2.4:2.8 for DCM1/TDCM/TIN/MBIN. The performance of the MBIN-based electroluminescent device can be improved dramatically by co-doping. The co-doping of TPA (tris-(4-(2-phenylethynyl)-phenyl)amine) gave rise to a decrease in the turn-on voltage, from 6.2 to 5.1 V; an increase in the maximum luminance, from 2934 cd m^-2 (at 15 V) to 6791 cd m^-2 (at 16.5 V); an enhancement in the maximum current efficiency, from 3.13 (132 cd m^-2) to 6.14 cd A^-1 (405 cd m^-2); and a shift in the CIE coordinates, from (0.65,0.35) to (0.66,0.33). TPA may act as a bridge to make the energy transfer from PVK to TPA then to MBIN more effectively than that from PVK directly to MBIN.Finally, we investigated two kinds of WOLED with hole blocking layer. (1) A very simple method was presented to realize white light emitting. The holes blocking layer-BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) results in a mixture oflights from NPB molecules (blue-light) and Alq₃ molecules (olivine-light). The chromaticity can be readily adjusted by only varying the thickness of the BCP layer. The CIE coordinates of the device are largely insensitive to the driving voltages. The maximum brightness is 5740 cd m^-2, the EL efficiency is 2.12 cd A^-1 at the applied voltage of 18V. (2) We designed and synthesized a new orange starburst DCM derivative-Tris(4-(2-(N-butyl-1,8-naphthalimide) ethynyl)phenyl)amine (TNGT). By doping TNGT in a PVK (poly(9-vinylcarbazole)) emissive layer we fabricated a white OLEDs with the configuration ITO (indium tin oxide) /PVK (70nm)/BCP (4 nm)/PVK: TNGT (20 wt.-%) / BCP (6nm)/Alq₃ (15nm)/LiF (0.3nm)/Al (150nm) exhibits a chromaticity coordinate of (0.33, 0.31) at an applied voltage of 12V; a maximum brightness is 2740cd m^-2 at the applied voltage of 16V.