Flexible, fast and freestanding UV sensors by printing of networked materials

The fabrication of microelectronics via additive manufacturing holds previously inaccessible potential compared to cleanroom-based technologies. Printing electronics is comparably simple and cost-efficient. The main advantage, however, lies in the choice of materials. While cleanroom-based fabrication always has a two-dimensional topology, printed electronics can involve inherently complex-shaped micro- and nanoparticles with outstanding functionalities. This work reports on an approach for the assembly of flexible, ultraviolet light (UV) sensors involving complex-shaped tetrapodal zinc oxide (t-ZnO) particles and carbon nanotubes via direct ink writing (DIW). The morphology of these particles eliminates the need for traditional methods of processing; instead, they can be processed through printing a particle-laden polymer solution. This approach enables to shape the functional t-ZnO particles in a facile and fast manner. A subsequent laser milling process removes the binder polymer from the top layers and exposes the semi-embedded particles, effectively forming a UV sensor. This sensor then exhibits a UV responsivity of 0.29 ± 0.01 µA/(W/cm 2 ) and an UV on off current ratio of over 500 in a span of 10 s while maintaining the flexibility of the binder polymer. This flexibility also allows the attachment of the sensor to a great variety of surfaces and surface geometries and facilitates the formation of free-standing structures. The sensors flexibility and I on /I off ratios are maintained up to a bending radius of 5 mm and also under cyclic mechanical deformation, which tested up to 1000 cycles.