title: New hole transporting materials based on di- and tetra-substituted biphenyl derivatives for organic light-emitting diodes.
abstract: This study aimed to synthesize novel hole transporting materials (HTMs) with biphenyl derivatives that are di- or tetra-substituted with naphthylphenyl amine groups and/or methoxy groups, and to examine systematically the variations of the properties of the HTMs with the number and location of the substituents. The tetranaphthylphenyl amine-substituted biphenyl-based HTMs T1N and T2N were observed to have better thermal properties than the commercial HTM NPB, with decomposition temperatures above 500 degrees C, and a 10 degrees C higher T(g). In EL devices with ITO/2-TNATA-(60 nm)/HTM(15 nm)/Alq3(70 nm)/LiF(1 nm)/Al structures, the disubstituted biphenyl-based HTMs with an asymmetric molecular structure D1N and D2N were found to have inferior luminescence efficiencies when compared to NPB, which has a symmetric molecular structure. However, M1N, which is substituted with a further two methoxy groups, was found to exhibit excellent luminance and power efficiencies, 4.88 cd/A and 1.36 Im/W respectively at 100 mA/cm2, which are higher by about 147% and 127% respectively than those of NPB (3.30 cd/A and 1.07 Im/W at 100 mA/cm2), due to better charge balance.
authors.affiliation: Department of Polymer Science and Engineering, Chungju National University, Chungju 380-702, Korea.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Chol-Min
authors.initials: CM
authors.lastname: Shin
authors.forename: Young-Il
authors.initials: YI
authors.lastname: Park
authors.forename: Jong-Wook
authors.initials: JW
authors.lastname: Park
authors.forename: Sung-Ryong
authors.initials: SR
authors.lastname: Kim
authors.forename: Min-Chul
authors.initials: MC
authors.lastname: Chung
authors.forename: Ji-Hoon
authors.initials: JH
authors.lastname: Lee