Charge transport in liquid-crystalline phthalocyanine-based thin-film transistors

TL;DR

This study explores how metal coordination, molecular order, and environment influence charge transport in liquid-crystalline phthalocyanine-based thin-film transistors, revealing key factors for optimizing organic electronic devices.

Contribution

It provides a detailed correlation between vibrational signatures and electronic performance, highlighting environmental effects and molecular structure on charge transport in these materials.

Findings

Enhanced current response under ultrahigh vacuum conditions.

Low activation energies for thermally activated mobility.

Environmental species suppress intrinsic charge transport.

Abstract

We investigate a series of liquid-crystalline phthalocyanines (metal-free and Cu, Zn, Ni, Co complexes) by correlating their vibrational signatures with their electronic performance in organic thin-film transistors (OTFTs). Raman spectroscopy reveals metal-dependent distortions of the phthalocyanine macrocycle, reflected in systematic shifts of the C-N-C and M-N vibrational modes. When integrated into OTFTs, all compounds exhibit markedly enhanced current response under ultrahigh vacuum compared to an N2-rich environment, demonstrating that intrinsic charge transport is strongly suppressed by atmospheric species. Temperature-dependent measurements (100-300 K) show clear threshold-voltage shifts driven by deep interface and bulk traps, while all devices display thermally activated mobility with low activation energies (14-20 meV). These results highlight how mesomorphic order, metal coordination, and environmental conditions collectively govern charge transport in liquid-crystalline phthalocyanines, offering design guidelines for their use as orientable semiconducting materials in organic electronics.