Researchers print UV photodetectors on plastic
Unlike other printed ZnO-based UV photodetectors reported so far in scientific literature, their devices do not require expensive precursor inks nor high temperatures for annealing the deposited ZnO film. Everything can be done in ambient conditions, at temperatures below 150ºC.
flexible PET substrate.
Described in a paper titled “Fully Aerosol-Jet Printed, High-Performance Nanoporous ZnO Ultraviolet Photodetectors” published in the ACS Photonics journal, the process involves an Aerosol Jet Printing (AJP) process whereby a dispersion ink of ZnO nanocrystals is blown at high pressure over the surface to be printed. The nozzle generates a mist of the material which, after compression by a virtual impactor, is directed toward the deposition head. Integrated in the printing head is a second influx of inert gas that sheathes the aerosol gas stream and guides it to the substrate. No clogging and very
versatile a process, claim the researchers, while the aerosol jet printing fabrication method can accommodate inks with viscosities ranging from 1 to 1000 cP.
Ink drying can be controlled by tuning the temperature of the substrate and the feed tube to the printing head, and the printed structures can then be thermally annealed or laser sintered.
scanning electron microscopy (SEM) images of
the ZnO film, showing the polycrystalline porous film.
The magnified image shows the hexagonal symmetry
of the ZnO nanocrystals with large surface to volume ratio.
As the solvent evaporates, a well-connected porous ZnO film forms, characterized by a high surface roughness. When printed as an overlap over two silver electrodes to form a metal−semiconductor− metal (MSM) photodetector, the high surface to volume ratio of the ZnO film makes the
sensor particularly sensitive, with a reported ON/OFF ratio circa 106 and short response times in the ultraviolet spectrum ranging from 250nm up to 400nm.
Exhibiting a low dark current, these low-cost flexible UV photodetectors had a performance comparable to more expensively crafted state-of-the-art nanostructured ZnO photodetectors, reports the paper.
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