Transparent, Broadband, Flexible, and Bifacial-Operable Photodetectors Containing a Large-Area Graphene–Gold Oxide Heterojunction

In this study, we combine graphene with gold oxide (AuO_<i>x</i>), a transparent and high-work-function electrode material, to achieve a high-efficient, low-bias, large-area, flexible, transparent, broadband, and bifacial-operable photodetector. The photodetector operates through hot electrons being generated in the graphene and charge separation occurring at the AuO_<i>x</i>–graphene heterojunction. The large-area graphene covering the AuO_<i>x</i> electrode efficiently prevented reduction of its surface; it also acted as a square-centimeter-scale active area for light harvesting and photodetection. Our graphene/AuO_<i>x</i> photodetector displays high responsivity under low-intensity light illumination, demonstrating picowatt sensitivity in the ultraviolet regime and nanowatt sensitivity in the infrared regime for optical telecommunication. In addition, this photodetector not only exhibited broadband (from UV to IR) high responsivity3300 A W^–1 at 310 nm (UV), 58 A W^–1 at 500 nm (visible), and 9 A W^–1 at 1550 nm (IR)but also required only a low applied bias (0.1 V). The hot-carrier-assisted photoresponse was excellent, especially in the short-wavelength regime. In addition, the graphene/AuO_<i>x</i> photodetector exhibited great flexibility and stability. Moreover, such vertical heterojunction-based graphene/AuO_<i>x</i> photodetectors should be compatible with other transparent optoelectronic devices, suggesting applications in flexible and wearable optoelectronic technologies