Gerwin Gelinck1 2 Albert van Breemen1 Hylke Akkerman1 Daniel Tordera1 Santhosh Shanmugam1 Bart Peeters1 Giulio Simone2 Rene Janssen2

1, TNO, Eindhoven, , Netherlands
2, TU Eindhoven, Eindhoven, , Netherlands

In this presentation we will give an update on our work on organic photodetectors for curved X-ray detectors, reflective pulse oximetry and retinal implants.

We have previously reported X-ray detectors on very thin plastic substrates with medical-grade performance using a solution-processed organic bulk heterojunction photodetector. This greatly simplifies the manufacturing process, opening the door to lower-cost photodetectors. As a next step, we show their advantage when curved.

Curved surfaces are the most natural shape for photodetectors – just think of the human eyeball. As a proof-of-concept, our detector-on-plastic was curved and then integrated into a Dental Cone-beam Computer Tomography (CBCT) X-ray system. CBCT is a technology that creates three-dimensional reconstructions of objects based on two-dimensional X-ray images. The curved detector’s more uniform image quality combined with enhanced reconstruction algorithms allowed the proof-of-concept system to deliver better 3D reconstructions than previous solutions. Our detector-on-foil furthermore allows the volume of 3D X-ray imaging systems to shrink by as much as 50%.

Using a low-bandgap polymer we have realized solution-processed OPDs that efficiently absorb light up to ca. 950 nm with the aim to use them as noninvasive reflective pulse oximeters. Our approach is to develop a 16x16 sensor array capable of measuring the perfusion of the microvascular tissue by means of photoplethysmography (PPG). The use of light reflection instead of tissue transillumination, enables noninvasive monitoring from virtually any skin surface.

Many research groups are working hard to develop implants for the blind. Here, organic photodetectors on plastic offer a unique chance: their softness allows them to interface intimately with neurons so that electrical signals generated by organic (semi)conducting materials are translated into bio-signals and vice versa. We will show that it is beneficial to connect organic photovoltaic cells in series by stacking them in the vertical direction: Series-connected sub-cells decrease the areal pixel current density but the higher photovoltage improves the impedance matching to the surrounding tissue and thus effectively enhances the injected current per pixel. This opens the way to generate large electrical signals without sacrificing areal density (as is the case with silicon). These advantages present a strong case for basing retinal implants on organic photovoltaic arrays on thin, flexible plastic substrates; however, this technology is still largely to be explored.