Large-Area Synthesis of Ultrathin, Flexible, and Transparent Conductive Metal-Organic Framework Thin Films via a Microfluidic-Based Solution Shearing Process

Abstract

Iminosemiquinone-linker-based conductive metal-organic frameworks (c-MOFs) have attracted much attention as next-generation electronic materials due to their high electrical conductivity combined with high porosity. However, the utility of such c-MOFs in high-performance devices has been limited to date by the lack of high-quality MOF thin-film processing. Herein, a technique known as the microfluidic-assisted solution shearing combined with post-synthetic rapid crystallization (MASS-PRC) process is introduced to generate a high-quality, flexible, and transparent thin-film of Ni-3(hexaiminotriphenylene)(2) (Ni-3(HITP)(2)) uniformly over a large-area in a high-throughput manner with thickness controllability down to tens of nanometers. The MASS-PRC process utilizes: 1) a micromixer-embedded blade to simultaneously mix and continuously supply the metal-ligand solution toward the drying front during solution shearing to generate an amorphous thin-film, followed by: 2) immersion in amine solution for rapid directional crystal growth. The as-synthesized c-MOF film has transparency of up to 88.8% and conductivity as high as 37.1 S cm(-1). The high uniformity in conductivity is confirmed over a 3500 mm(2) area with an arithmetic mean roughness (R-a) of 4.78 nm. The flexible thin-film demonstrates the highest level of transparency for Ni-3(HITP)(2) and the highest hydrogen sulfide (H2S) sensing performance (2,085% at 5 ppm) among c-MOFs-based H2S sensors, enabling wearable gas-sensing applications.