Inkjet-printed Light-emitting Devices: Applying Inkjet Microfabrication to Multilayer Electronics

This work presents a novel means of producing thin-film light-emitting devices, functioning according to the principle of electroluminescence, using an inkjet printing technique. This study represents the first report of a light-emitting device deposited completely by inkjet printing. An electroluminescent species, doped zinc sulfide, was incorporated into a polymeric matrix and deposited by piezoelectric inkjet printing. The layer was printed over other printed layers including electrodes composed of the conductive polymer poly(3,4-ethylenedioxythiophene), doped with poly(styrenesulfonate) (PEDOT:PSS) and single-walled carbon nanotubes, and in certain device structures, an insulating species, barium titanate, in an insulating polymer binder. The materials used were all suitable for deposition and curing at low to moderate (<150°C) temperatures and atmospheric pressure, allowing for the use of polymers or paper as supportive substrates for the devices, and greatly facilitating the fabrication process. The deposition of a completely inkjet-printed light-emitting device has hitherto been unreported. When ZnS has been used as the emitter, solution-processed layers have been prepared by spin-coating, and never by inkjet printing. Furthermore, the utilization of the low-temperature-processed PEDOT:PSS/nanotube composite for both electrodes has not yet been reported. Device performance was compromised compared to conventionally prepared devices. This was partially due to the relatively high roughness of the printed films. It was also caused by energy level misalignment due to quantization (bandgap widening) of the small (