Low-temperature processing of porous zinc-oxide for flexible sensing applications

Three-dimensional nanostructured networks are proposed as a means of substantially improving functional materials through a combination of maximised surface area, and exceptional morphological connectivity. The formation of nanoscale junctions (i.e., primary bonds) between constituent nanostructures facilitates tremendous enhancements to interfacial conductivity and structural integrity, thereby offering magnitudes of improvement over the pristine morphologies formed by weak Van der Waals contacts. However, integration with temperature sensitive polymers, and thin metal electrodes in wearable devices preclude the use of conventional approaches such as thermal sintering. This work investigates the use of solvent vapour as a low-temperature means of rapidly eliciting high-quality nanojunctions in highly porous zinc-oxide nanoparticle networks. The proposed method is an effortless, inexpensive, and easily scalable processing strategy, capable of generating interparticle necking in the matter of minutes. In testing as a UV photodetector at a low operation bias of 1 V, the vapour enhanced network produced a 128,000-fold improvement in responsivity (20.6 A/W at 365 nm, 1 μW/cm²) over the pristine structure, and a 5300-fold improvement over a thermally produced network; meanwhile maintaining exceptionally low dark currents (~143 pA). The low temperature synthesis and exceptional performance further suggest high potential adaptability of this material as a wearable UV sensor.