title: Spin-assembled nanolayer of a hyperbranched polymer on the anode in organic light-emitting diodes: the mechanism of hole injection and electron blocking.
abstract: We introduced a spin-assembled nanolayer of hyperbranched poly(ether sulfone) with sulfonic acid terminal on top of an indium-tin oxide anode in organic light-emitting diodes. This results in great improvement in luminous efficiency, better than that of devices using a commercially available conducting polymer composition as a hole-injection layer. The effect of the nanolayer was investigated by impedance spectroscopy, photovoltaic measurement for built-in-potential, and transient electroluminescence. We concluded that the high luminous efficiency resulted from the efficient electron-blocking by the nanolayer and hole-injection assisted by the accumulation of electrons at the interface. This result implies that, for an efficient hole-injection layer, the electron-blocking capability should be incorporated in addition to the hole-injection and -transport capability.
authors.affiliation: Samsung Advanced Institute of Technology, Gyeonggi-do, Korea. twlee@postech.ac.kr
authors.forename: Tae-Woo
authors.initials: TW
authors.lastname: Lee
authors.forename: Jong-Jin
authors.initials: JJ
authors.lastname: Park
authors.forename: Young
authors.initials: Y
authors.lastname: Kwon
authors.forename: Teruaki
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Tae-Lim
authors.initials: TL
authors.lastname: Choi
authors.forename: Jong Hyeok
authors.initials: JH
authors.lastname: Park
authors.forename: Rupasree Ragini
authors.initials: RR
authors.lastname: Das
authors.forename: Masa-aki
authors.initials: MA
authors.lastname: Kakimoto