A new perspective on WO3: Bridging ultrafast terahertz spectroscopy and photoelectrochemical characterization

Abstract

The efficient conversion of solar energy into chemical fuel remains a critical challenge in renewable energy research. Photoelectrochemical cells (PECs) offer a promising route by directly using sunlight to drive water splitting. However, their widespread implementation is limited by the insufficient efficiency and stability of available semiconductor materials. Rapid discovery and optimization of high performance PEC photoelectrodes require advanced screening methods capable of providing deep insights into charge transport, carrier dynamics and interfacial processes. Herein we propose a novel characterization strategy that integrates optical pump terahertz probe (OPTP) spectroscopy with electrochemical impedance spectroscopy (EIS) to investigate structure–property relationships in WO₃ thin films. By employing silicon substrates to simulate semiconductor depletion layers, we establish a new approach for bridging in situ electrochemical techniques with ex situ time-resolved THz spectroscopy, leading to a more comprehensive understanding of the PEC relevant properties. Our methodology allows the rapid evaluation of charge-carrier dynamics, transport efficiency and interfacial charge transfer processes, providing critical insights into material performance. Using WO₃ as a well established system, we demonstrate that synthesis temperature plays a pivotal role in shaping the morphology, crystallinity and electronic properties of the films. A significant increase in photocurrent and charge-carrier mobility is observed for WO₃ annealed at 700 °C, which is attributed to enhanced crystallization and reduced charge recombination. Additionally, a conductive interfacial layer, identified through independent X-ray photoelectron spectroscopy (XPS) and EIS measurements, further influences charge transport behavior. Moreover, the results highlight the intricate relationship between processing conditions, electronic structure and PEC efficiency, offering new perspectives for designing optimized photoelectrodes. In this study we propose a high throughput, AI compatible framework for PEC material screening, leveraging OPTP spectroscopy as a rapid, non-destructive technique for evaluating carrier dynamics. The proposed methodology may not only accelerate the discovery of next generation PEC materials but also of fundamental insights into semiconductor–electrolyte interactions, paving the way for more efficient and stable PEC devices.