An ambipolar to n-type transformation in pentacene-based organic field-effect transistors

We report an ambipolar to n-type transformation in pentacene-based organic field-effect transistors (OFETs) of aluminum (Al) source-drain electrodes. The hole currents of the ambipolar OFETs were decreased by over two orders of magnitude within 24 h after the device fabrication, but the electron currents remained unchanged, which makes the devices present n-type only characteristics. The transformation is correlated with the interfacial interactions between Al electrodes and pentacene, as characterized by analyzing near-edge X-ray absorption fine structure spectra and Micro-Raman spectra. This study highlights the importance of metal/organic interfaces in the performance of OFETs, and demonstrates decent n-type pentacene-based OFETs with electron mobility of 0.1 cm²/V/s with proper annealing treatment.