Halide perovskite photoelectrodes for solar water splitting: Advances and stability challenges

Photoelectrochemical water splitting has emerged as one of the most promising strategies for direct production of green hydrogen, an energy carrier with high energy density and zero carbon emissions. Among recent developments, halide perovskite semiconductors have attracted significant attention due to their outstanding optoelectronic properties, including strong light absorption, high charge carrier mobility, and tunable bandgaps. The integration of halide perovskites as light-absorbing layers in synergy with charge transport, protective, and catalytic layers into photoelectrode architectures has yielded promising scalability, high photocurrent densities, and extended operational stability. This review examines the role of each material that constitutes photoelectrodes based on halide perovskites and summarizes key evaluation parameters, namely photocurrent density, overpotential, and operational stability. In addition, a framework for conducting the electrochemical characterization of the devices is discussed, and key strategies commonly employed for selecting materials that reach high photocurrent densities and extended operational stability are outlined. Although performance metrics are extracted at thermodynamic potentials of oxygen (1.23 V) and hydrogen (0 V) evolution reactions, stability studies show that even small deviations in applied bias accelerate degradation processes, such as hydration, halide migration, and interfacial corrosion. As a result, current tests duration typically ranging from minutes to hundreds of hours remain as the main bottleneck, outweighing the already demonstrated high photocurrents and efficiencies. Key challenges include photocurrent retention, chemical and structural stability under prolonged operation, and the need for more robust transport layers and encapsulation strategies capable of mitigating degradation mechanisms induced by voltage, light, as well as water contact.