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Abstract

Flexible sensors play an increasing role in printed electronics and are of interest for optoelectronic applications in flexible robotics and industrial automation. Thus, we have investigated the hybrid inorganic-organic junction between ZnO and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate). A thin ITO (indium tin oxide) layer on PET (polyethylene terephthalate) foils was used as substrate electrode. ZnO was deposited from a nanoparticle (NP) suspension by electrophoretic deposition. For comparison, we have used three different methods for the deposition of PEDOT:PSS, namely (i) drop casting, (ii) dip-coating, (iii) inkjet printing. For the resulting ZnO-PEDOT:PSS junctions, current-voltage characteristics were recorded using miBot micromanipulators, and analysed applying adapted models of thermionic emission, according to Cheung and Cheung, as well as Norde. For dip-coated samples we obtained barrier heights of (0.78±0.01) eV and (0.73±0.02) eV, respectively, while inkjet printed and drop casted structures show smaller values (0.53 eV to 0.66 eV, respectively). Thus, dip-coating can be used for a rapid upper estimation of the ZnO-PEDOT:PSS barrier heights for developing inkjet printable optoelectronic sensors. When using low concentrated PEDOT:PSS suspensions, we observed negative photoresponse of the junction; this is consistent with the formation of a ZnO-NPs and PEDOT:PSS nanocomposite which we obtained on porous semi-transparent ZnO-NP films.

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