Signatures of Band-like Charge Carrier Transport in a Three-Dimensional Fe-HHTP Metal–Organic Framework

Abstract

Abstract Metal–organic frameworks (MOFs) offer exceptional structural and chemical tunability, and the emergence of electrically conductive variants creates new opportunities for functional optoelectronic materials. Here, we investigate charge transport in a three-dimensional (3D) Fe-HHTP MOF (or Fe-CAU-42), composed of hexahydroxytriphenylene (HHTP)-based supertetrahedral units and trimeric Fe(III) oxo cluster nodes arranged in a diamond structure. Temperature dependent Van der Pauw (vdP) electrical conductivity measurements reveal an Arrhenius-type thermally activated charge transport mechanism operating in pelletized samples. Terahertz time-domain spectroscopy is used to probe the frequency-resolved complex conductivity of the Fe-HHTP pellet. The THz conductivity spectra are well-described by the Drude–Smith model, indicating the presence of mobile charge carriers with band-like dynamics subject to backscattering and localization. Temperature-dependent conductivity analysis reveals that the increase in conductivity with temperature is governed primarily by changes in carrier density rather than by changes in scattering time (and hence mobility). DC conductivities ranging from 6.54 × 10–3 S cm–1 at 300 K to 1.22 × 10–3 S cm–1 at 77 K are extracted from modeling of the THz data, in excellent agreement with van der Pauw measurements. The combined results establish a transport picture in which charge motion is dominated by localized band-like charge carriers with thermally activated carrier density, providing direct insight into carrier dynamics in conductive 3D catecholate MOFs.