Deciphering the carrier dynamics enhancement in WO3-containing composites: an ultrafast transient reflectance investigation

Abstract

In recent years, the quest for WO₃-based composites with expanded optical absorption and elevated photocatalytic and photoelectrochemical performance has intensified. Despite these pursuits, a clear mechanistic understanding of the efficiency gains has been a missing piece, hindering further optimization. This study uses the transient reflectance (TR) technique to probe the intricacies of carrier dynamics in WO₃, Li_0.1WO₃, and the FeOOH/Li_0.1WO₃ composite, and found that under near-ultraviolet (NUV) illumination, the FeOOH/Li_0.1WO₃ system demonstrates a photo-carrier lifetime that is approximately twofold and tenfold longer than that of Li_0.1WO₃ and WO₃, respectively. Moreover, under near-infrared (NIR) irradiation, the FeOOH/Li_0.1WO₃ composite sustains carriers for nearly four times longer than the Li_0.1WO₃ counterpart. Our in-depth analysis points to the hole-filling effect from lithium intercalation and the FeOOH-mediated passivation of oxygen vacancies as the dual drivers behind the significantly extended carrier lifetimes, which favor processes such as charge separation, transfer, extraction, and storage. By employing femtosecond TR measurements to dissect the photo-carrier behavior in these systems, this study sheds light on the intrinsic mechanisms that have been obscured using traditional approaches. This work aims to contribute pivotal insights, potentially paving the way for the next generation of high-performance WO₃ composites in energy conversion technologies.