Printed photodiodes enable filter-less visible light communications

March 02, 2020 //By Julien Happich
photodiodes
Researchers from the Karlsruhe Institute of Technology (KIT) have demonstrated a multichannel visible light communication (VLC) system based on printed organic photodiodes (OPDs) capable of demultiplexing optical signals emitted at different wavelengths without the need for additional optical filters.

Describing their findings in a paper titled “Color‐Selective Printed Organic Photodiodes for Filterless Multichannel Visible Light Communication” published in the Advanced Materials journal, the authors report a filter-less concept for inkjet‐printed colour‐selective OPDs which exploits the selective absorption of a bulk‐heterojunction (BHJ) system where selected nonfullerene acceptors (NFAs) are blended into a transparent wide‐bandgap polymer donor serving as the printing matrix.


Colour-selective organic light sensors produced by inkjet printing
with semiconducting inks. Courtesy of Noah Strobel, KIT.

In this approach, the authors demonstrated, the device spectral response solely depends on the choice of the NFA while the polymer donor dictates the rheological properties of the ink, removing any interdependence between processing parameters and the optical properties of the active layer, hence greatly simplifying ink formulations.

Printed OPDs reported in the paper had responsivities in excess of 10 2mA W −1 in the blue/green and red visible spectral range, again without the requiring any optical filtering, with bandwidths in excess of 1.5MHz. These characteristics make the printed organic photodiodes suitable for use in a VLC system, where colour selectivity could be exploited to de‐multiplex optical signals simultaneously transmitted at different wavelengths. Such photo detector arrays could be made not only cost-effectively but also thin and flexible for better mechanical integrations into wearables, mobile sensor nodes, or health care monitoring systems.
“High numbers of these photodetectors of any design can be produced on flexible, light materials. Hence, they are particularly suited for mobile devices,” said lead author Noah Strobel.

Karlsruhe Institute of Technology (KIT) - www.kit.edu

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