Institute of Solid State Physics


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Inkjet printed organic photodiode on an ultra-thin transferrable polymer substrate
Bernhard Burtscher
11:15 - 12:15 Wednesday 12 December 2018 PH01150

Wearable electronics but also Lab-on-Skin devices (i.e. those skin-contact devices meant to measure physiologically relevant parameters or biosignals, such as temperature, hydration of the human skin or ECG among others) gained a lot of interest in recent years. The use of novel materials and manufacturing processes are indeed enabling a new generation of ultra-thin, transferrable imperceptible electronic devices for multiple applications.
As main requirements, such devices need to adhere and conform to human skin or other target surfaces with complex topography and should not be noticeable while worn. Thus materials have to satisfy certain requirements, namely flexibility, stretchability or even transparency in some specific cases (as regards to e.g. optoelectronic devices), among others.
Organic materials are mostly suitable to satisfy these demands and many of them can be adapted to large area and continuous manufacturing processes, such as printing. Printing techniques have the advantage that they are typically fast, resource-friendly, can be easily scaled up and with low cost in contrast to vacuum-based production methods.

In this work an organic photodiode (OPD) is fabricated onto a commercially available thin and transferrable polymer substrate using printing techniques, mainly drop-on-demand inkjet printing.
Different commercially available candidates were considered as substrate materials. Two different kinds of decal transfer temporary tattoo-papers and a medical adhesive were investigated regarding their thickness, roughness, wettability and optical transmittance.
The OPD is then fabricated with two transparent electrodes (namely, printed conducting polymer PEDOT:PSS and Ag nanowires) enabling its use from both sides and thus enhancing its application potential. Furthermore, the bulk heterojunction diode consists of an inkjet printed mixture of water-soluble polythiophene and fullerene derivatives, with no need of aggressive solvents.

Figure 1 shows how such an OPD can look like and how it could be included in an electrical circuit. Ideally this circuit would also be printed or at least large parts of it. Then this whole device could be transferred onto the desired target surface, whether it is skin or an artificial surface. OPD on a temporary tattoo is easily transferred onto a target surface by wetting the back paper carrier substrate, same as in temporary tattoos for kids.
While it is an objective that this photodiode can be transferred onto human skin, and therefore it needs to be bio-compatible, it should also be applicable to other surfaces like glass or a brick wall for example.

In a device such OPD could allow for receiving optical signals or observing blood oxygen level due to pulse oximetry.


Figure 1: Picture of an OPD prototype (before transfer), schematic integration into electric circuit and transfer onto a target surface.