Highly Tunable, Broadband, and Negative Photoresponse MoS₂ Photodetector Driven by Ion-Gel Gate Dielectrics

Revealing the light-matter interaction of molybdenum disulfide (MoS₂) and further improving its tunability facilitate the construction of highly integrated optoelectronics in communication and wearable healthcare, but it still remains a significant challenge. Herein, polyvinylidene fluoride and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PVDF-EMIM-TFSI) ion-gel are employed to replace the oxide to fabricate a MoS₂-based phototransistor. The high capacitance enables a large tunability of the carrier concentration that results in ambipolar transport of MoS₂. It is found that the photoelectrical effect of the MoS₂ ion-gel phototransistor can be greatly tuned by the gate voltage including its photoresponsivity, detectivity, and response wavelength. An abnormal negative photoelectrical effect in both the electron branch and the hole branch is observed which is due to the adsorption/desorption of the C₂F₆NO₄S₂^- ion. By tuning the carrier concentration, the photoresponse can be extended from the visible region to the short infrared region. At 1200 nm, the photoresponse and detectivity can be tuned as large as 0.90 A/W and 1.88 × 10¹¹ Jones, respectively. Ultimately, by combining the tunability of gate voltage and wavelength, it is demonstrated that the photoelectrical effect is dominated by the photogating effect in the hole carrier, while it is coregulated by a photogating and photothermal effect in electron carrier. This study provides new insights for developing a highly tunable broadband photodetector with low consumption.