Distinct Hole and Electron Transport Anisotropy in Ambipolar Nickel Dithiolene-Based Semiconductor.

Abstract

Understanding anisotropic charge transport in molecular semiconductors is crucial for device optimization, yet its intricate dependence on orbital-specific intermolecular interactions and molecular packing remains a challenge, especially in ambipolar systems. In ambipolar semiconductors, where both holes and electrons participate in conduction, distinct molecular orbitals prompt a critical inquiry: can orbital variations result in coexisting yet distinct anisotropic transport properties within a single component? We confirm this possibility by demonstrating that the air-stable nickel dithiolene, Ni(4OPr), exhibits such behavior. Despite its herringbone stacking implying a two-dimensional electronic structure, Ni(4OPr) uniquely exhibits distinct intermolecular interactions for hole (HOMO-to-HOMO; HOMO = highest occupied molecular orbital) and electron (LUMO-to-LUMO; LUMO = lowest unoccupied molecular orbital) transport. Crucially, this leads to highly anisotropic hole transport pathways, while electron pathways are remarkably isotropic, demonstrating a stark contrast in their transport anisotropies. Leveraging the high crystallinity, grazing-incidence wide-angle X-ray scattering (GIWAXS) determined in-plane molecular orientation. This enabled experimental verification of distinct anisotropic hole and electron transport, directly governed by orbital-specific intermolecular interactions, in an ambipolar molecular semiconductor. Our findings, demonstrating coexisting yet distinct anisotropic transport properties for both carriers within a single component, significantly advance the understanding of ambipolar molecular semiconductors and broaden their scope for future device applications.