Solution processed tandem solar cells for water electrolysis

Abstract

Green hydrogen production via solar-driven water splitting stands as a pivotal technology for transitioning to a carbon-neutral economy. While photovoltaic-electrochemical (PV-EC) systems offer a promising pathway by driving water electrolysis as a practical route to solar hydrogen production, single-junction solar cells typically fail to provide the sufficient photovoltage required to drive water electrolysis without external bias. Tandem solar cells, particularly utilizing solution-processable materials, have emerged as a viable solution to overcome this thermodynamic barrier while offering the benefits of low-cost fabrication and mechanical flexibility. This review critically examines recent advancements in solution-processed tandem architectures for unassisted solar water splitting, classifying them into three primary categories: all-organic, all-halide perovskite, and perovskite-organic hybrid tandem systems. We elucidate how bandgap engineering and spectral splitting strategies in these architectures enable high open-circuit voltages (>1.6 V) and improved solar-to-hydrogen efficiencies, reaching up to 17.8%. Beyond material optimization, this article highlights the importance of system-level integration, including the engineering of interconnecting layers, geometric area matching between PV and catalysts, and the development of earth-abundant electrocatalysts for minimizing kinetic overpotentials. Finally, we provide a forward-looking perspective on overcoming critical bottlenecks such as long-term stability in aqueous environments and scalability, aiming to guide future research toward practical and economically viable solar fuel production.