Unveiling the Origin of the Scale-Dependent Conductivity of Ni3(HITP)2 Metal–Organic Framework Thin Films

Abstract

Conductive metal–organic frameworks (MOFs) are crystalline, intrinsically porous materials that combine remarkable electrical conductivity with exceptional structural and chemical versatility. This rare combination makes these materials highly suitable for a wide range of energy-related applications. However, the electrical conductivity in MOF-based devices is often limited by the presence of different types of structural disorder. Here, the electrical transport characteristics of high quality Ni3(HITP)2 nanometer-thin films are reported. These findings reveal a tenfold difference in conductivity between the micro- and nano-scale, attributed to poor electrical connection among a limited number of crystalline grains. Average in-plane conductivity values at the micro- (σIP,micro = 0.7 ± 0.3 S cm−1) and nano- (σIP,nano = 6 ± 3 S cm−1) scales is determined, and the value of the inter-grain resistance, Rinter-grain = 40 kΩ is found. Using a 2D resistor network model with a 40 kΩ base resistance and scattered higher resistances, surface potential maps of in-operando MOF-based electrical devices are successfully reproduced. Additionally, a structure–property relationship that links the density and spatial distribution of electrical failures in inter-grain connections to the observed micro-scale conductivity in MOF thin films is established.