High Mobility Pentacene/C60-Based Ambipolar OTFTs by Thickness Optimization of Bottom Pentacene Layer

In this paper, we investigated the dependence of ambipolar carriers transport on the thickness of bottom pentacene layers in a series of pentacene/C₆₀ heterojection based ambipolar organic thin-film transistors (OTFTs). It was found that hole transport increased monotonically, while the electron transport increased at first and then decreased, with the increasing bottom pentacene layer thickness from 1.5 to 9 nm. The morphologies evolution of both pentacene and C₆₀ layers, investigated by atomic force microscopy measurement, demonstrated the effect mechanism of the bottom pentacene layer thickness on the device performance of ambipolar OTFTs. The almost saturated hole mobility of 0.39 cm²/Vs and the highest electron mobility of 6.3 cm²/Vs were achieved in an optimized ambipolar OTFT with a 4.5-nm-thick pentacene layer.