From biased cells to artificial leaves: A device-centric review of solar chemical transformations

Photoelectrochemical (PEC) systems are rank among the most promising platforms for converting solar energy into storable fuels such as hydrogen, formate, and ammonia. Unlike suspension-based photocatalysis or photovoltaic-electrolysis hybrids, PEC devices integrate light absorption and catalytic conversion within a single architecture, offering unique advantages in system simplicity and cost potential. Yet despite impressive laboratory advances, widespread deployment of PEC remains limited by photovoltage deficits, sluggish reaction kinetics, materials instability, and the absence of standardized benchmarking protocols. This review provides a comprehensive overview of the state-of-the-art in PEC performance, organized by system architecture—ranging from single absorbers and PV-assisted tandems to monolithic artificial leaves. Key performance metrics are defined and compared across applications including water splitting, CO 2 reduction, and paired organic/nitrate valorization. The review also outlines typical testing protocols and device configurations used in the field. Through this architecture- and metric-based perspective, we identify the critical trade-offs and technological bottlenecks that must be addressed to realize scalable, bias-free PEC fuel production.