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

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 (Φ_B) at the Au/fullerene-doped TPA interface decreases to 0.021 eV upon using C₇₀ as a dopant, and Φ_B of Au/TPA is as large as 0.37 eV. The reduced Φ_B of 0.021 eV satisfies the condition for ohmic contact at room temperature (Φ_B [Formula: see text] 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.