Time-resolved terahertz (THz) spectroscopy and open-circuit photovoltage measurements were employed to examine the size-dependent charge carrier dynamics of tungsten(VI) oxide (WO3) particles for their use as the photoanode in photoelectrochemical cells. Specifically, films of commercially available WO3 nanoparticles (NPs) and granular particles (GPs) with diameters of 77 ± 34 and 390 ± 260 nm, respectively, were examined in air and while immersed in 0.1 M Na2SO4 electrolyte (pH = 2). Examination of the frequency-dependent transient photoconductivity at short and long time scales indicates the presence of both photoinduced high net transport charge carriers at early times and in some cases low net transport charge carriers at later times. The high net transport charge carriers dominate the photoconductivity signal for ∼100 ps after photoexcitation. Depletion of the short-lived high net transport carriers due to trapping leads to the detection of longer-lived low net transport photoinduced charge carriers that likely contribute to surface chemistry.
