Facile modification of Cu source–drain (S/D) electrodes for high-performance, low-voltage n-channel organic thin film transistors (OTFTs) based on C60

Abstract

Exploring suitable electrode materials with sufficiently low work function, ambient stability and low-cost is of great technological importance to the development of n-channel OTFTs. Here, we show that the work function of Cu can be effectively reduced from 4.65eV to 4.28eV through surface modification via simply spin-coating a thin layer of branched polyethylenimine (PEI). By exploiting a high-capacitance density gate dielectric (200nF/cm2), low-voltage (3V) C60 TFTs with electron mobility (μe) of 3.2cm2/Vs are demonstrated with PEI modified Cu as source–drain (S/D) electrodes. In contrast, the device with Cu S/D electrodes possesses μe of only 1.0cm2/Vs. The improvement in electrical performance of the PEI modified device is attributed to the efficient electron injection at the Cu/C60 interface which resulted from the reduction in work function of Cu. Moreover, upon PEI modification, the bias stability of the device can be obviously enhanced as compared to the unmodified one, and the resultant device exhibits an excellent thermal stability up to 200°C without appreciable degradation in mobility. The facile modification of low-cost Cu as S/D electrodes for high-performance n-channel OTFTs as well as the low-voltage operation will pave the way for large scale manufacturing of organic electronics.