Out-of-Plane Photodetectors on Flexible Substrates Using Printed Technologies

Optoelectronic devices like photodetectors (PDs) are essential in numerous applications such as high-speed optical communications, robotics, healthcare, and biomimetic visual systems, all of which require light detection and interaction. Consequently, a diverse types of PDs have been developed on planar substrates, utilizing various light-sensitive materials and traditional micro- and nano-fabrication techniques. Recently, significant efforts have focused on creating highly sensitive PDs with flexible designs and eco-friendly nanoscale materials and methods. This has led to the exploration of resource-efficient manufacturing based on printed electronics, which allows PDs with out-of-plane configurations to unlock new opportunities for optoelectronics and sustainable manufacturing. In this work, we present an optimization of a drop-on-demand (DoD) high-resolution electrohydrodynamic (EHD) jet printing method for creating 3D gold (Au) micropillars. Arrays of Au micropillar electrodes (MEAs) with heights up to 196 µm and an aspect ratio of 52 are successfully printed. Additionally, a seedless synthesis of zinc oxide (ZnO) nanowires (NWs) on the printed Au MEAs is achieved by combining additive manufacturing with the hydrothermal growth method. This hybrid approach results in hierarchical networks of light-sensitive NWs, demonstrating effective ultraviolet (UV) sensing through the fabrication of flexible PDs. The 3D PDs exhibit excellent omnidirectional light absorption, maintaining high photocurrents across a wide range of light incidence angles (±90°). Finally, the PDs are tested under bending conditions to showcase their remarkable mechanical flexibility. The presented study demonstrates the potential of high resolution EHD-based jet printing toward 3D conductive and functional structure fabrication using solution processing and opens new directions for high-performance 3D flexible electronics.