Electronic structure of stable n-type semiconducting molecular complex (diC8-BTBT)(TCNQ) studied by ultraviolet photoemission and inverse photoemission spectroscopy

Abstract

The electronic structure of a semiconducting mixed-stack charge transfer (CT) complex composed of a 2,7-dialkyl[1]benzothieno[3,2-b][1] benzothiophene (diC8-BTBT) electron donor and a tetracyanoquinodimethane (TCNQ) electron acceptor, (diC8-BTBT)(TCNQ), was studied by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. Compared with its components, the frontier electronic states observed for the (diC8-BTBT)(TCNQ) complex showed a large stabilization that originates from the reconstruction of electronic states by intermolecular donor-acceptor CT interactions. We discuss how the frontier electronic states of the complex are formed from those of the individual component molecules, and clarify the origin of the air-stable n-type organic field-effect transistor characteristics that the material exhibits when it is used as a channel semiconductor.