Donor-Acceptor Interaction in Films of Tetracene–Tetracyanoquinodimethane Heterostructures and Composites

Abstract

The structures and the absorption and photovoltaic spectra of thin films of tetracene (TC) and tetracyanoquinodimethane (TCNQ), as well as the films of their heterostructures (TC/TCNQ) and composites (TC + TCNQ), have been studied. The heterostructures and composites are obtained by the thermal sputtering of the components – successively or simultaneously, respectively – in vacuum. The photovoltaic spectra were measured, by using the condenser method. It is found for the first time that the largest changes ΔD1 in the TC/TCNQ and TC + TCNQ absorption spectra with respect to the sum of the absorption spectra of the components are observed in the intervals of TCNQ dimeric bands at 2.214 eV (ΔD1 < 0) and in all TC bands (ΔD1 > 0). Those changes testify to the formation of charge transfer complexes between the TC (the electron donor) and TCNQ (the electron acceptor) molecules at the interfaces in the TC/TCNQ heterostructures and in the bulk of TC + TCNQ composites, which is also confirmed by the appearance of TC+- and TCNQ−-bands in the photovoltaic spectra of both the heterostructure and composite films. This result is important for a deeper understanding of the operating mechanisms in various potentially imaginable devices based on those heterostructures and composites (solar cells, field-effect transistors, and light-emitting diodes).