Light effects on graphene/tungsten disulfide nanotubes/graphene heterostructure

Abstract

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.

Keywords: disulfide; graphene; heterostructure; nanotubes; tungsten.