Laser-induced electrodes towards low-cost flexible UV ZnO sensors

Flexible electronics is a branch of electric fabrication that allows for increasingly ergonomic devices. However, its production still requires multi-step, expensive, and time-consuming processes. Laser-direct writing (LDW) is a clean and low-cost alternative technique for producing electrodes on flexible substrates with high resolution, without the need of masks or direct contact with the device. Laser-induced graphene (LIG), a particular type of LDW, is a technique in which, by the irradiation of polyimide (PI) and polyetherimide (PEI) films with a pulsed CO₂ infrared laser, a photothermal reaction occurs which leads to the formation of stacked graphene structures. LIG thus emerges as a rising substitute to produce graphene-based devices. This work consists of the development and optimization of flexible UV sensors with zinc oxide nanostructures as the active layer for photodetection, PI or PEI as the substrates, and the respective LIG as electrodes. The nanostructures with higher area-volume ratio, synthesized through a microwave-assisted hydrothermal method, were selected and deposited by drop-casting onto electrodes that in turn were optimized to enhance electrical properties by varying the laser parameters. The assembled sensors were able to successfully detect UV radiation with a responsivity of 92 and 2 nA W^-1 for 1 V bias for the PI and PEI substrates, respectively. In addition, the PI sensor has shown to be capable of working under strain and to be stable after several hours of constant cyclic operation.