Self-powered semitransparent/flexible doped-graphene/WS2 vertical-heterostructure photodetectors

A combination of semi-metallic graphene and photosensitive two-dimensional (2D) transition metal dichalcogenide for heterostructures is ideal for high-performance optoelectronic device applications. Here, we first report semitransparent/flexible photodetectors (PDs) employing trifluoromethanesulfonyl-amide (TFSA)-doped graphene (GR) (TFSA-GR)/WS2 vertical heterostructures. The TFSA-GR/WS2 PDs show a delta-function-like photo-/dark-current (or on/off) ratio-vs-voltage behavior at zero bias, irrespective of wavelength (λ), meaning "self-powered", mainly resulting from the surface doping of GR. The photoresponse is very sensitive in a wide ultraviolet-to-visible λ range. Maximum key figures of merit obtained for the PDs: responsivity (R), external quantum efficiency, and detectivity are 0.14 AW−1, 40%, and 2.5 × 109 cm Hz1/2 W−1, respectively, comparable to or even larger than those of previously-reported self-powered and/or hetero-structured PDs. The average transmittance of the PDs in the visible region is about 40%, indicating their semitransparency. The PDs maintain 88% of the initial R even after bending tests at 4 mm bending radius for 3000 cycles, demonstrating the excellent flexibility.