Phase behavior and electrical transport in DBTTF-HATCN donor-acceptor mixtures

TL;DR

This study investigates the phase behavior, structure, and electrical transport properties of donor-acceptor mixtures of DBTTF and HATCN, revealing new phases, improved conductivity, and insights into charge transport mechanisms.

Contribution

It provides detailed analysis of how mixing ratios affect the structure and electrical properties of DBTTF-HATCN mixtures, introducing new phases with enhanced charge transport.

Findings

Formation of new donor-acceptor complex phase with distinct crystal structure

Electrical conductivity varies non-monotonically with composition and is generally improved

All compositions exhibit n-type behavior except pristine DBTTF

Abstract

The formation of donor-acceptor complexes (DACs) between the electron donor Dibenzotetrathiafulvalene (DBTTF) and the acceptor Hexaaza\-triphenylene\-hexacarbo\-nitrile (HATCN) results in a new phase with a distinctly different crystal structure as well as new optical absorption bands below the energy gaps of the two pristine materials. X-ray scattering and atomic force microscopy provide detailed insights into the film structure and morphology by systematic variation of the mixing ratio from pristine DBTTF to pristine HATCN. The measured electrical conductivity of thin films depends in a highly non-monotonic manner on the composition of the mixture and shows significantly improved charge transport compared to the pristine films. The temperature-dependent conductivity, charge carrier concentration, and mobility were investigated across these compositions. Surprisingly, all compositions exhibited n-type behavior, except for pristine DBTTF. This behavior is explained by the electronic structure of the mixtures, as revealed by ultraviolet photoelectron spectroscopy, which indicates that charge injection and transport occur via the lowest unoccupied molecular orbital of the DAC and HATCN. Additionally, the observed electrical conductivity is strongly influenced by morphology and structural ordering of the films. These findings offer valuable insights for the design of advanced materials with enhanced electrical performance.