A team at Karlsruhe Institute of Technology (KIT) has demonstrated a multichannel visible light communication system based on an organic photodetector array capable of demultiplexing optical signals without the need for additional optical filters. The researchers engineered a special ink formulation to print wavelength-selective bulk heterojunction organic photodetectors onto flexible carriers. They incorporated nonfullerene acceptors in a transparent polymer donor matrix to narrow and tune the optical response in the visible range without optical filters or light management techniques. In the KIT team’s approach, the optical properties of the bulk heterojunction system are decoupled from the viscoelastic ink properties. The spectral response of the device depends solely on the choice of nonfullerene acceptor, while the polymer donor dictates the properties of the ink. This removes any interdependence between processing parameters and the optical properties of the active layer. It eliminates the need for devising new ink formulations when selecting a different nonfullerene acceptor and simplifies the process of developing and printing filterless, wavelength-selective organic photodetectors. Color-selective organic light sensors produced by inkjet printing with semiconducting inks. Courtesy of Noah Strobel, KIT. The printed organic photodiodes exhibited excellent charge-carrier dynamics in spectroscopic tests. The color selectivity and high performance of the photodiodes were demonstrated in a filterless visible light communication system capable of demultiplexing intermixed optical signals. The team believes that the simplicity of its approach, which simultaneously addresses functionality and fabrication, could offer a path toward facile integration of wavelength-selective optical sensing elements in future printed electronic applications. It could find particular use in applications requiring a high degree of personalization, high fabrication throughput, and cost-effectiveness, such as wearable devices, 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,” researcher Noah Strobel said. The research was published in Advanced Materials (www.doi.org/10.1002/adma.201908258).