Spray deposition of Polyethylenimine thin films for the fabrication of fully-sprayed organic photodiodes

Abstract

In the last years, a big effort has been put into the investigation of the scalability of deposition processes for organic optoelectronics to achieve large-scale and cost-effective fabrication of functional devices. One of the most prominent techniques that promises to obtain an easy-to-scale production is spray-deposition; however, so far, the feasibility of entirely spray-deposited optoelectronic devices has not yet been demonstrated. To fulfill this goal, in this work we investigate the spray-coating of Polyethylenimine (PEI) and the effect of the process parameters on the film characteristics, in terms of thickness, work-function and roughness. The achievement of thin layers of PEI (∼10 nm) with full coverage is the last step towards the realization of lithography-free and vacuum-free organic electronic devices. For the first time, we show the fabrication of fully-sprayed organic photodiodes (OPDs), initially on patterned Indium-Tin Oxide, and subsequently on bare glass. The resulting photodiodes yield peak EQE above 65% and dark currents lower than 10-4 mA/cm2 at a reverse bias of -4 V. Moreover, both the cathode and anode electrode of the OPDs fabricated with the described process-flow are semi-transparent, granting the simultaneous collection of two different light signals from the top and the bottom side.Graphical abstract