An ultra-fast, self-powered and flexible visible-light photodetector based on graphene/Cu2O/Cu gradient heterostructures

Abstract

Cuprous oxide (Cu₂O) is widely used in optoelectronic devices, because of its nontoxicity, high light absorption coefficient, native p-type conductivity and high hole mobility. Herein, a visible-light photodetector based on a graphene/Cu₂O/Cu device is synthesized by novel thermal oxidation of Cu foil with the assistance of carbon powder and mechanically transferring the monolayer graphene onto the surface of the Cu₂O. At zero bias voltage, the graphene/Cu₂O/Cu visible-light photodetector exhibits an ultra-fast response time of 4.1 μs at 530 nm, a responsivity of 86 mA W⁻¹ at 550 nm and excellent visible-light selectivity. Besides, the graphene/Cu₂O/Cu device maintains high responsivity even after being bent thousands of times to a radius of curvature of 30 mm. Cross-sectional TEM and EDX measurements indicate that the ratio of copper to oxygen in the Cu₂O film increased gradually from the surface to the inside, which induces an inherent built-in electric field along the normal direction of the Cu₂O absorption layer and consequently a rapid separation of photo-generated carriers. Our research provides a new approach for developing self-powered flexible visible-light photodetectors with low cost, high efficiency and quick response.