Home About us Contact
|
Home About us Contact | ||
|
|
||
Low Turn-on Voltage (low + turn-on_voltage)
Selected AbstractsA Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl-Substituted Fluorene Units for Highly Efficient Blue ElectrophosphorescenceADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Fang-Ming Hsu Abstract Highly efficient blue electrophosphorescent organic light-emitting diodes incorporating a bipolar host, 2,7-bis(diphenylphosphoryl)-9-[4-(N,N -diphenylamino)phenyl]-9-phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6-difluoro-phenyl)pyridinato- N,C2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron-donating (p-type) triphenylamine group and an electron-accepting (n-type) 2,7-bis(diphenyl-phosphoryl)fluorene segment linked through the sp3 -hybridized C9 position of the fluorene unit. The lack of conjugation between these p- and n-type groups endows POAPF with a triplet energy gap (ET) of 2.75,eV, which is sufficiently high to confine the triplet excitons on the blue-emitting guest. In addition, the built-in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF-based device doped with 7,wt% FIrpic exhibits a very low turn-on voltage (2.5,V) and high electroluminescence efficiencies (20.6% and 36.7,lm W,1). Even at the practical brightnesses of 100 and 1000,cd m,2, the efficiencies remain high (20.2%/33.8,lm W,1 and 18.8%/24.3,lm W,1, respectively), making POAPF a promising material for use in low-power-consumption devices for next-generation flat-panel displays and light sources. [source] Synthesis and electroluminescent properties of polyfluorene-based conjugated polymers containing bipolar groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Sheng-Tung Huang Abstract A bipolar dibromo monomer, bis-(4-bromophenyl)[4-(3,5-diphenyl-1,2,4- triazole-4-yl)-phenyl]amine (9), containing electro-rich triphenylamine and electro-deficient 1,2,4-triazole moieties was newly synthesized and characterized. Two fluorescent fluorene-based conjugated copolymers (TPAF, TPABTF) were prepared via facile Suzuki coupling from the dibromo bipolar monomer, 4,7-dibromo-2,1,3-benzothiadiazole (BTDZ), and 9,9-dioctylfluorene. They were characterized by molecular weight determination, IR, NMR, DSC, TGA, solubility, absorption and photoluminescence spectra, and cyclic voltammetry. The polymers showed good solubility in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran, and dichlorobenzene at room temperature. They had glass transition temperatures (Tg) higher than 135 °C and 5% degradation temperatures in nitrogen atmosphere were higher than 428 °C. Single layer polymer light-emitting diodes (PLED) of ITO/PEDOT:PSS/polymer/metal showed a blue emission at 444 nm and Commission Internationale de I'Eclairage (CIE) 1931 color coordinates of (0.16, 0.13) for TPAF. The device using TPABTF as emissive material showed electroluminescence at 542 nm with CIE1931 of (0.345, 0.625), low turn-on voltage of 5 V, a maximum electroluminance of 696 cd/m2, and a peak efficiency of 2.02 cd/A. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6231,6245, 2009 [source] Synthesis and white electroluminescent properties of multicomponent copolymers containing polyfluorene, oligo(phenylenevinylene), and porphyrin derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Hui Li Abstract Two novel multicomponent copolymers (P1 and P2) containing polyfluorene (PF), oligo(phenylenevinylene) (OPV), and porphyrin (Por) derivatives were synthesized according to the Suzuki polymerization method. The structures, optical, and electrochemical properties of the two model compounds (OPV and Por) and multicomponent copolymers were characterized by 1H NMR, FTIR, elemental analysis, UV,vis spectroscopy, photoluminescence, and cyclic voltammetry, respectively. Both of the copolymers exhibit thermotropic liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. Electroluminescence spectra of these copolymers exhibit broadband emissions covering the entire visible region from 400 to 700 nm. The single layer polymer light emitting diodes device based on P2 with a configuration of indium tin oxide/poly(ethylenedioxythiophene):poly(styrenesulfonic acid)/polymers/Ca/Al emits white light with the Commission Internationale de l,Eclairage chromaticity coordinates of (0.29, 0.30), maximum brightness of 443 cd/m2. The white-light-emitting devices based on the novel multicomponent copolymers exhibit low turn-on voltage, and good color stability at different driving voltages as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5291,5303, 2009 [source] Synthesis and characterization of new carbazole/fluorene-based derivatives for blue-light-emitting devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2006Saulius Grigalevicius Abstract 2,7-Bis(9-ethylcarbazol-3-yl)-9,9-di(2-ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350,370 °C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long-wavelength region even after annealing at 200 °C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn-on voltage (4.0 V), and brightness of about 400 cd/m2. The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m2 at ,11 V) and demonstrated luminescence efficiency of 0.8 cd/A. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5987,5994, 2006 [source] PCPP derivatives containing carbazole pendant as hole transporting moiety for efficient blue electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2009Jinwoo Kim Abstract The syntheses and characterization of poly((2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4H -cyclopenta[def]phenanthrene))- co -(2,6-(4,4-bis(4-(((9-carbazolyl)hexyl)oxy)phenyl))-4H- cyclopenta[def]phenanthrene)) (BCzPh-PCPPs) and poly((2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4H -cyclopenta[def]phenanthrene))- co -(2,6-(4-(4-(((9-carbazolyl)hexyl)oxy)phenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)-4H- cyclopenta[def]phenanthrene))) (CzPh-PCPPs), with carbazole unit as pendants, are presented. The carbazole moiety, which can improve the hole injection ability, was introduced as a pendant on the PCPP backbone. The devices of the polymers with the configurations of ITO/PEDOT:PSS/polymers/Ca/Al generate EL emission with maximum peaks at 400,450 nm, CIE coordinates of (x = 0.11,0.29, y = 0.11,0.33), low turn-on voltages of 4,6 V, maximum brightness of 60,810 cd/m2, and luminescence efficiencies of 0.04,0.22 cd/A. The PL spectra of CzPh-PCPPs films did not show any peak at around 550 nm, which corresponds to keto defect or aggregate/excimer formation, even after annealing for 30 h at 150 °C in air. Out of the series, CzPh-PCPP1 (PCPP derivative with 10% of carbazole moiety as pendant) shows blue emission with the maximum brightness of 810 cd/m2 at 9 V, and the highest luminescence efficiency of 0.22 cd/A at 395 mA/cm2. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1327,1342, 2009 [source] A New Class of Blue-Emitting Materials for LED Applications: Triarylamine N -Functionalised 2,7-Linked Carbazole PolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2007Hunan Yi Abstract Attachment of triarylamino-functional groups at the 9-position of 2,7-linked carbazole polymers results in blue-emitting materials with two independent redox processes that were attributed to the triarylamino groups and the polymer backbone, respectively. This new class of blue-emitting conjugated polymers was prepared via a Suzuki cross-coupling reaction and showed low turn-on voltages in electroluminescent devices as a result of their low ionisation potentials. The photophysical, electrochemical and electroluminescent properties of these materials are discussed. [source] | ||||||||||