Light effects on graphene/tungsten disulfide nanotubes/graphene heterostructure

In this study, we present a hybrid optoelectronic device consisting of tungsten disulfide nanotubes (NTs) deposited on graphene electrodes, forming ohmic contacts that enable efficient charge transport. The heterostructure is fabricated on a flexible polyethylene terephthalate substrate. Comprehensive electrical and optoelectronic characterizations are conducted under various environmental conditions, with a focus on photocurrent response and the photovoltaic effect. The device shows a broadband photoresponse from 405 to 900 nm, reaching its best performance at 880 nm, where it delivers a peak responsivity of 0.07 mA W^-1, a specific detectivity of 2.3 × 10⁷Jones and rise/decay constants of 1.6 s/1.5 s, measured under 405 nm illumination at an incident power of 0.19 mW. A long-time tail of 23 s is also observed, attributed to trap-assisted processes. The long-wavelength cut-off (∼ 880 nm) corresponds to an indirect bandgap of 1.4 ± 0.1 eV for the NTs. Under 520 nm illumination, the heterostructure generates an open circuit photovoltage of ∼15 mV and a short-circuit photocurrent of ∼0.08 nA, confirming the presence of a photovoltaic effect. Illumination at 405 nm reveals a photocurrent response that is sensitive to changes in environmental pressure. These results highlight the multifunctionality of the heterostructure, which can be optimized for photovoltaic conversion, wearable photodetectors, and sensing applications.