Charge injection phenomena at the contact interface between (5,10,15,20-tetramethylporphyrinato)cobalt(ii) and 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane single crystals

Abstract

The contact interface of heterogeneous organic crystals is used in a wide variety of electronic devices. In recent years, it has become clear that the function of electrical conduction occurs at the heterojunction interface. As a result, the development of new functions at the surface of organic crystals is expected, which requires further investigations. Herein, we assess the charge transfer phenomena and the conductivity at the interface between electron-donor–acceptor crystals. The interface is prepared using (5,10,15,20-tetramethylporphyrinato)cobalt(II) (CoTMP) and 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F₂TCNQ) as the donor and acceptor crystals, respectively. The surface resistivity of the CoTMP/F₂TCNQ interface is extremely low (3 × 10⁵ Ω sq⁻¹), which is one of the lowest values reported thus far for this type of interface. Scanning probe microscopy and electron spin resonance measurements show that 11% of the charge is injected into this interface by contact, and the charge diffusion distance is 200 nm. This distance is significantly higher than the film thickness used in conventional semiconductor devices, thereby indicating that this technique can contribute to the development of organic electronics.