Inkjet printing is so good at positioning and meting out the right quantity of material that it can be used not just for producing documents, but in industry as well--for example, to fabricate solar cells (see www.laserfocusworld.com/articles/330748) or to create etch patterns for photodiode arrays (see www.laserfocusworld.com/articles/311575). Now, scientists at Arizona State University (ASU; Tempe, AZ) and the University of Oulu (Oulun Yliopisto, Finland) are using the process to print quantum-dot LEDs (QDLEDs). Not only does inkjet printing conserve expensive QD-containing fluid; it also allows for the possibility of patterning full-color pixelated displays (although the printer that the scientists are using now can print only a single color at a time). In one example, quantum dots with a cadmium selenide core, zinc sulfide shell, and a capping organic ligand were obtained from Evident Technologies (Troy, NY) and used as received; the QDs were suspended in chlorobenzene to create ink. The substrate, a piece of glass precoated with the transparent conductor indium tin oxide (ITO), was coated with a 20 nm layer of poly-TPD, which was then cross-linked and served as the hole-transport layer.
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