Broadband, Flexible, Skin-Compatible Carbon Dots/Graphene Photodetectors for Wearable Applications

Abstract: The development of wearable photodetectors demands a unique combination of broadband optical sensitivity, mechanical flexibility, and skin-compatibility, with these requirements rarely met simultaneously by existing technologies. Here, we present photodetectors that combine all of these performances. This is achieved by integrating carbon dots, engineered for extended ultraviolet-to-near-infrared absorption, with single-layer graphene transferred onto a plastic substrate. Unlike traditional quantum dot systems, our carbon dots achieve a broad ultraviolet-to-near-infrared response without toxic heavy metals. Graphene provides an efficient channel for charge transport, while a biocompatible chitosan-glycerol electrolyte enables efficient, low-voltage carrier modulation, with peak performance at approximately 0.5 V gate bias. The resulting photodetectors exhibit a broadband photoresponse with responsivities of approximately 0.19 A/W at 406 nm, 0.32 A/W at 642 nm, and 0.18 A/W at 785 nm. They maintain consistent performance at a bending radius of 0.8 cm with negligible degradation after repeated cycles. Furthermore, skin-compatibility assessments using the SkinEthic model confirm the non-toxic nature and suitability of our devices for direct skin contact. The combination of broadband absorption (400-800 nm), flexibility, and skin-compatibility, along with low-voltage operation ($<$ 1.5 V), positions our photodetectors as promising building blocks for next-generation wearable optoelectronics.