Directly probing the charge transport in initial molecular layers of organic polycrystalline field effect transistors

Abstract

We report the charge transport in pentacene polycrystalline organic thin film transistors (OTFTs) with different active layer thicknesses, ranging from a sub-monolayer, bilayer, to tens of nanometers by employing a novel electrode-contact architecture. Temperature dependent electrical characterization is systematically carried out to elucidate the carrier transport mechanisms of OTFTs based on various active layer thicknesses. The mobilities of charge carriers in the GB region of the whole channels are extracted and analyzed by utilizing a two-dimensional (2D) grain boundary model (2DGB). The roles of grain boundaries (GBs) in electrical behavior should be to some degree reduced as the second layer begins to form. Due to the vertical interlayer transfer via which charge carriers can bypass the most resistant GB regions, the conductance path energetic disorder degree is reduced, simultaneously, the hopping transport undergoes crossover from the 2D to 3D one. Our results will deepen the understanding of the interface charge transport in the OTFTs, and provide pathways for organic material and device optimization.