Photocurrent study of all-printed photodetectors on paper made of different transition metal dichalcogenide nanosheets

We have inkjet-printed in-plane ‘metal–semiconductor–metal’ type photodetectors on paper, one of the cheapest flexible substrates, which is also recyclable and foldable, in contrast to traditional plastic substrates. The photodetectors are made by using graphene as electrodes and various transition metal dichalcogenides(TMDs) as photoactive component. In particular, we have tested MoS₂, WS₂, MoSe₂ and MoTe₂. Large differences in responsivity and sensitivity were observed for all of the TMDs measured, with MoS₂ showing the highest sensitivity and MoTe₂ producing the largest response. However, photodetectors made of MoTe₂ show a large decrease in responsivity after one week of exposure to air. The wavelength dependence of the responsivity in MoS₂ based devices was further analyzed using a supercontinuum photocurrent spectroscopy setup, with the results suggesting a bolometric or photoelectric origin of the signal. We also report some simple approaches to enhance the device performance and tune the energy range at which the maximum in responsivity or sensitivity is observed.