Pressure-induced phase transitions and broadband photoresponse in layered 2D MoO3

This work investigates the pressure-dependent structural evolution and optoelectronic behavior of MoO3 under high pressure to 37.8 GPa, combining in situ Raman spectroscopy, x-ray photoelectron spectroscopy, photocurrents, electrical conductivity, and theoretical calculations. Two distinct phase transitions in α-MoO3 were observed: first to the MoO3-II phase at about 10.1 GPa, followed by conversion to the high-pressure MoO3-III phase at about 25.3 GPa. This structural evolution correlated with exceptional optoelectronic enhancement, demonstrating a 434-fold increase in the photocurrent density (from 0.0628 to 29.10 mA cm−2) and the corresponding responsivity (from 1.366 to 632.7 mA W−1) under 365 nm illumination at 37.8 GPa, relative to the corresponding values at 1.2 GPa. These enhancements arise from pressure-induced increases in electrical conductivity, bandgap narrowing, and improved light absorption. Notably, the high-pressure MoO3-II and MoO3-III phases exhibit photodetection extending into the near-infrared band (980 nm). These anomalous phenomena can be attributed to the formation of oxygen vacancies, which introduce in-gap states positioned below the conduction band minimum, thereby facilitating efficient carrier excitation across both visible and infrared spectral regions. The findings highlight high-pressure engineering as an effective approach to optimize the optoelectronic performance of MoO3, advancing its potential utility in photodetector systems.