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Inkjet-printing of conductive components for the manufacturing of a quantum dot based sensor for optical health monitoring

: Ortlepp, F.; Hartwig, M.; Moebius, M.; Martin, J.; Otto, T.; Gessner, T.; Baumann, R.R.

Baumann, R. ; TU Chemnitz, Institut für Print- und Medientechnik:
Printing Future Days 2015. Proceedings : 6th International Scientific Conference on Print and Media Technology for Junior Scientists and PhD Students, October 05 - 07, 2015, Chemnitz, Germany
Berlin: VWB Verlag für Wissen und Bildung, 2015
ISBN: 978-3-86135-626-4
ISBN: 3-86135-626-0
Printing Future Days <6, 2015, Chemnitz>
Fraunhofer ENAS ()

In contrast to conventional sensors, quantum dot based sensors enable the direct detection and optical indication of stressed components. [1] Current manufacturing methods require cost intensive vacuum and clean room technology to deposit relatively rare occurring materials like indium tin oxide (ITO). Inkjet-printing technology is known for cost efficient prototyping up to large-scale industrial manufacturing of conductive transparent layer formations. Therefore inkjet-printing technologies enable the stepwise replacement of cost intensive cleanroom or vacuum deposition methods like sputtering or e.g. the deposition of cost intensive materials like ITO.
By applying inkjet-printing technology the first ITO free sensor for mechanical load detection, based on charge carrier sensitive photoluminescence (PL) quenching of quantum dots was manufactured.
By applying external voltages the PL was quenched to high quenching contrasts of approx. 5 % of initial PL intensity. In a practical scenario the external voltage source can be replaced by a piezoelectric foil, which inject charge carriers to indicate stressed components by PL quenching.
The sensor includes a sputtered Aluminum (Al) bottom electrode, a spin-coated active PL layer with quantum dots (QDs) embedded in semi-conducting poly(9-vinylcarba-zole) (PVK) and an inkjet printed poly(3,4-ethylenedioxythio-phene) polystyrene sulfonate (PEDOT:PSS) top electrode. The Al bottom electrodes are characterized by layer heights of approx. 63 nm and the active PL layer has a maximum height of approx. 115 nm. The layer height of the printed PEDOT:PSS top electrodes depend on the printing parameters and are characterized by a maximum height of 100 nm. To reach this layer heights the wetting of inkjet inks on quantum dot (QD) based composites was analyzed in detail and improved by nitrogen plasma pre-treatment technologies.
The sensor sensitivity in combination with the optical indication was improved by optimized separation of the quantum dot composite layers. For further investigations the bottom electrodes were printed with a nano-particle based silver ink and PEDOT:PSS, to analyze the interaction with subsequent deposited active PL layers. In this correspondence the electrodes were analyzed in terms of morphology and electrical resistance.
In order to extend the field of application a first flexible quantum dot based ITO free sensor on a foil-based substrate was realized. The foil based flexible sensor enables the integration in curved lightweight-composites and proves the practical implementation.