Abstract
Generation of ultrathin, transferable, and imperceptible electronic devices [e.g., organic photodiode (OPD)] for multiple applications, such as personalized health monitors and wearables, is emerging due to the continuous development of materials and manufacturing processes. For such devices, the choice of a suitable substrate is of utmost importance. A water decal transfer from a temporary tattoo paper is adopted here as a substrate for ultrathin and conformable organic components because of easy and reliable transfer of a ≈600 nm robust and transparent polymer nanofilm of ethyl cellulose. Strategies for the fabrication of a transferable OPD on a temporary tattoo are investigated. A device with an overall thickness <1 μm and its performance after transfer are demonstrated. Then, efforts are put into fabricating an OPD by inkjet printing with a water-soluble active layer consisting of polythiophene and fullerene derivatives to aid cost- and material-efficient, large-scale production possibilities. Additionally, a second semitransparent electrode made of printed aluminum-doped zinc oxide and silver nanowires is used to allow usage from both sides to enhance the application potential. Both OPD examples presented here need improvement of the device performance but permitted us to highlight the versatility and application potential of temporary tattoos for transferable components. Target surfaces for the final application after transfer include artificial (flat and smooth, e.g., glass, or even complex and rough, e.g., concrete, paper, and so forth) as well as natural ones.
Highlights
Wearable electronics[1] and lab-on-skin devices[2] have gained a lot of interest over the last few years
Because of the foreseen organic photodiode (OPD) application, a first question regarded the suitability of tattoo paper (TT) to act as a transferable substrate; we investigated its transparency in the visible light range, stability against wet or vacuum processing, its thickness, and whether its surface is smooth enough to enable fabrication and operation of an OPD
The investigation on transferable substrates started with a preliminary screening of different commercially available TTs and a medical polyurethane adhesive recently adopted for skin-mounted sensors.[5,38,39]
Summary
Wearable electronics[1] and lab-on-skin devices[2] have gained a lot of interest over the last few years. While the use of Ag NWs would, in principle, allow for a better conductivity after annealing (150 °C, 30 min),[47] on TT, this proved to be challenging because of the limited temperature stability of EC.[22,48,49] in a previous study on the same TT paper, heating of a sample at 150 °C resulted in partial degradation of surface roughness due to recrystallization upon heating of EC, which could be detrimental for the operation of the OPD.[22] different processing strategies should be adopted To this aim, a layer of AZO was first printed before depositing Ag NWs, permitting us to achieve an electrode with a lower sheet resistance (RS = (12.4 ± 5.1) Ω/□). The extent to which this affects the performance of the device should be evaluated with respect to a particular application since mechanical durability, electrical and temperature insulation, and moisture protection depend on the application and on the target surface
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