Manipulating the ambipolar characteristics of pentacene-based field-effect transistors

We report on the ambipolar charge transport modulation of organic semiconductors (OSCs) in field-effect transistors (FETs) based on joint experimental and theoretical studies. We investigated pentacene, one of the most widely studied OSCs, as an example to achieve efficient and balanced ambipolar FETs (i.e., electron mobility is as fast as hole mobility) via fine control of the interfacial properties of the active channel. Through elimination of the interfacial tension of the active channel, ultrahigh performance pentacene-based ambipolar FETs were achieved, with electron and hole mobilities both near 3.0 cm² V^-1 s^-1 in the same channel. Theoretical investigation of the pentacene molecule showed that the electron density is mainly located on the terminal ends but the hole density is on the centered three aromatic rings, a finding that provides insight into the difficulty of observing high electron mobility levels compared with hole mobility in FETs. Analysis of theoretical vibrational reorganization energy supports that electron transport between pentacene molecules suffers from more serious interfacial effects than hole transport. With the help of theoretical calculations, Raman spectroscopy can be used to characterize pentacene films at an early stage of growth at the nanometer scale to assess the ambipolar transport potential in FETs. The results demonstrate an excellent connection between ambipolar characteristics in actual organic FETs and microscopic molecular-level properties, thereby advancing the design and synthesis of new OSCs for electronic and photonic applications.