Highly efficient hole injection from Au electrode to fullerene-doped triphenylamine derivative layer

Abstract

Triphenylamine derivatives are superior hole-transport materials. For their application to high-functional organic semiconductor devices, efficient hole injection at the electrode/triphenylamine derivative interface is required. Herein, we report the design and evaluation of a Au/fullerene-doped α-phenyl-4′-[(4-methoxyphenyl)phenylamino]stilbene (TPA) buffer layer/TPA/Au layered device. It exhibits rectification conductivity, indicating that hole injection occurs more easily at the Au/fullerene-doped TPA interface than at the Au/TPA interface. The Richardson-Schottky analysis of the device reveals that the hole injection barrier (ΦB) at the Au/fullerene-doped TPA interface decreases to 0.021 eV upon using C70 as a dopant, and ΦB of Au/TPA is as large as 0.37 eV. The reduced ΦB of 0.021 eV satisfies the condition for ohmic contact at room temperature (ΦBle 0.025 eV). Notably, C70 doping has a higher barrier-reduction effect than C60 doping. Furthermore, a noteworthy hole-injection mechanism, in which the ion–dipole interaction between TPA and fullerenes plays an important role in reducing the barrier height, is considered based on cyclic voltammetry. These results should facilitate the design of an electrode/organic semiconductor interface for realizing low-voltage driven organic devices.