Emission spectra and strain-dependent properties of flexible inkjet printed WSe2–graphene heterostructure photodetectors

Abstract

Heterostructures of WSe₂, a two-dimensional (2D) layered material, offer exciting opportunities for development of optoelectronics and sensors, including in flexible, conformal modalities. In this work, few layer WSe₂ was synthesized via liquid-phase exfoliation (LPE), where all inkjet printed WSe₂–graphene heterostructure photodetectors were assembled on flexible polyimide substrates and their optoelectronic transport properties were characterized. Molecular vibrational spectra were gathered using Raman spectroscopy as a function of temperature from 80 K to 573 K for the few-layer LPE processed WSe₂ membranes, from which we infer behaviors related to electron–phonon interactions and phonon lifetimes. The Raman-active E¹_2g and A_1g modes experienced a red-shift as temperature was raised, attributed to the lattice potential anharmonicity. The subsequent integration of the LPE-synthesized WSe₂ into photodetectors led to the validation of photoresponse toward incoming broadband white-light radiation, where the capacitance–frequency response was also measured. Here, the photoresponsivity was calculated to be ∼0.70 A W⁻¹, and other parameters such as detectivity and the linear dynamic range were also deduced. Temporal measurements revealed the rise and decay times of the photocurrent with respect to the power density, where the rising and falling edge time constants were within the hundred millisecond range. Strain-dependent measurements conducted with bending showed the photocurrent to decrease with increasing bending and strain, as expected. Finally, strain-dependent Raman measurements revealed a blue-shift and increase in emission intensity for both the in-plane and out-of-plane vibrational modes. Our results indicate the promise of heterostructure WSe₂ devices for large format photoabsorbers printed on flexible substrates using additive manufacturing approaches, where such devices will be attractive for light-weight wearable and airborne applications.