Vibrational spectroscopy on solution-dispersed MoS2for inkjet-printed photodetectors

Two-dimensional (2D) layered materials have shown promise for a wide range of semiconducting devices formed not only on rigid Si substrates, but also on low-cost, flexible substrates. Here, we present the temperature-dependent (similar to 80 K to 573 K) frequency shifts of the Raman-active E-2g(1) and A(1g) modes of multilayer molybdenum disulfide (MoS2), which exhibited a red shift with increasing temperature. The full-width-at-half-maximum (FWHM) for the E-2g(1) and A(1g) modes was found to increase with temperature allowing us to compute a reduction in phonon lifetime for our liquid-exfoliated multilayer MoS2 due to the greater disorder. After these spectroscopic studies, the semiconducting dispersion of MoS2 was then integrated with graphene ink, to create an integrated inkjet-printed heterostructure photodetector onto flexible substrates. The photodetector was photo-responsive to broadband incoming radiation in the visible regime, where the photo-responsivity R similar to 0.11 A/W and conductivity sigma similar to 5.9 x 10(-2) S/m were achieved at room temperature. This high sigma is due to the MoS2 flakes that provided a coherent film through additional rotary evaporator densification leading to less-trap density of the photo carrier. The detectivity D was calculated to be similar to 1.7 x 10(10) Jones at a low light intensity of 3.2 mW/cm(2), while the external quantum efficiency EQE was determined to be similar to 25% at wavelength lambda similar to 550 nm. The linear dynamic range (LDR) indicates the high sensitivity and low-phase noise of a photodetector which was also calculated to be similar to 11 dB at room temperature, while the gain G was similar to 0.469 at 0.8 mW/cm(2). With increasing intensity of the broadband incoming light source, the rise time and decay time of the photocurrent were measured for the first time for our inkjet-printed MoS2-graphene photodetector, setting the stage for future innovations in solution-processed 2D inorganic semiconductors.