Conductive, Large-Area, and Continuous 7,7,8,8-Tetracyanoquinodimethane@HKUST-1 Thin Films Fabricated Using Solution...

Most metal-organic frameworks (MOFs) have an insulating nature due to their porosity and redox-inactive organic components. The electrical conductivity of the prototypical MOF, HKUST-1, can be tuned by infiltrating a small-molecule organic semiconductor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), into the HKUST-1 pores, creating TCNQ@HKUST-1. However, current processes of creating TCNQ@HKUST-1 films have many roadblocks such as slow crystallization rates, which limit high throughput production, and the formation of Cu(TCNQ) as a byproduct, which affects the electrical conductivity and degrades the chemical structure of HKUST-1. In this work, we show that HKUST-1 films can be rapidly synthesized over large areas with consistent thickness and no pinholes via a meniscus-guided coating technique called solution shearing. The subsequent pore activation process and TCNQ impregnation can be completed via solvent exchange to minimize the formation of the Cu(TCNQ) byproduct, and we obtain an increase in electrical conductivity of the solution-sheared TCNQ@HKUST-1 thin films of over 7 orders of magnitude, reaching a maximum value of 2.42 × 10^-2 S m^-1 when TCNQ is incorporated for 10 days. The conductivity of solution-sheared TCNQ@HKUST-1 is higher compared to films formed by high-pressure pelletization of TCNQ@HKUST-1. We show that solution shearing can produce large-area thin films rapidly and reduce the formation of grain boundaries better than pelletization, allowing for large-area electronics with both charge transport and porosity for applications as sensors and electronics.