Monolithic and Flexible ZnS/SnO₂ Ultraviolet Photodetectors with Lateral Graphene Electrodes

A continuing trend of miniaturized and flexible electronics/optoelectronic calls for novel device architectures made by compatible fabrication techniques. However, traditional layer-to-layer structures cannot satisfy such a need. Herein, a novel monolithic optoelectronic device fabricated by a mask-free laser direct writing method is demonstrated in which in situ laser induced graphene-like materials are employed as lateral electrodes for flexible ZnS/SnO₂ ultraviolet photodetectors. Specifically, a ZnS/SnO₂ thin film comprised of heterogeneous ZnS/SnO₂ nanoparticles is first coated on polyimide (PI) sheets by a solution process. Then, CO₂ laser irradiation ablates designed areas of the ZnS/SnO₂ thin film and converts the underneath PI into highly conductive graphene as the lateral electrodes for the monolithic photodetectors. This in situ growth method provides good interfaces between the graphene electrodes and the semiconducting ZnS/SnO₂ resulting in high optoelectronic performance. The lateral electrode structure reduces total thickness of the devices, thus minimizing the strain and improving flexibility of the photodetectors. The demonstrated lithography-free monolithic fabrication is a simple and cost-effective method, showing a great potential for developement into roll-to-roll manufacturing of flexible electronics.