Collective Optimization of Synthesis and Printing for Improved Performance of ZnO Nanowires Based Large-Area Printed Sensors

ZnO nanowires (NWs) form an important building block for various types of sensors and field-effect transistors. However, owing to the known variability of ZnO structure morphologies, it is challenging to obtain ZnO NWs alone by using synthesis processes such as vapor phase transport. To address this challenge, we have performed a series of NW synthesis studies and discovered that it is difficult to eliminate ZnO nanoflakes during the growth stage. By optimizing the synthesis and printing method together, it is possible to reduce considerably the size and density of undesirable structures, such as printed flakes, to a level where they would not bridge the contacts of the device and thus not affect the device's performance. As proof of concept, the ZnO NWs-based UV photodetectors were realized using the contact printing method. The developed devices show the photo-to-dark current ratio of 104, a rise time of ∼3.1 s, and a decay time of 8.6 s. The removal of flakes contributes to the low level of dark current, which is critical to low power consumption. The presented results provide a promising route for ZnO NWs ensembles based large area sensing for applications such as electronic skin for humanoids, and more.