Highly‐Conductive and Micro‐Structured Transparent Glass Substrates for Efficient and Scalable Photoelectrochemical Applications

ABSTRACT Photoelectrochemical (PEC) cells use semiconductor‐based photoelectrodes to directly convert sunlight into storable electrochemical fuels like hydrogen. Recent advances in material efficiency and stability have sparked interest in scaling this technology for industrial implementation. This work identifies key upscaling challenges that hinder the performance of large‐area PEC devices, specifically: (1) ohmic losses in the electron‐conductive substrate of the photoelectrode; (2) inhomogeneities of the photoabsorber; (3) ionic transport limitations in the electrolyte; (4) (photo)active area losses from bubble accumulation; and (5) concentration polarization and pH gradient losses at the photoelectrode–electrolyte interface. The first two challenges were addressed using a laser‐ablation lithography‐assisted spray pyrolysis procedure to produce uniform, conductive, stable, and high‐surface‐area transparent glass substrates. Micrometer‐thick fluorine‐doped tin oxide current collectors enhanced conductivity, while surface texturization maximized surface area. Device architecture (PortoCell), electrolyte concentration, and flow rate were optimized to mitigate the remaining limitations. The final optimized system, tested using a conformal hematite (α‐Fe ₂ O ₃ ) thin film with ca. 49 cm ² of photoactive area, displayed a photocurrent density of ca. 0.63 mA cm ⁻² (1.45 V _RHE , 100 mW cm ⁻² ); the same performance of a reference photoelectrode with ca. 0.28 cm ² . Furthermore, the proposed optimized large‐area photoelectrode demonstrated an operational long‐term stability of ca. 1000 h.