Unassisted Water-Splitting with Perovskite-Perovskite Tandem Photocathodes at 18% STH Toward Commercially Relevant $2/kg H₂

Integrated photoelectrochemical devices have been proposed as a long-term, low-cost alternative to PV-electrolyzer systems for solar fuel production, but have historically lagged in performance metrics including efficiency, lifetime, and notably cost. We report technoeconomic analysis showing the critical role of photoabsorber and electrocatalyst cost in PEC devices, highlighting perovskite-perovskite tandems with low-PGM electrocatalyst loading as a platform capable of reaching $2/kg H₂. We demonstrate a technoeconomically-informed approach to PEC system design using a perovskite-perovskite tandem device encapsulated by a conductive adhesive-barrier. Through optimization of reactor design, electrolyte composition, and catalyst content, we show that the cost of unassisted PEC water-splitting can be reduced without compromising on stability or efficiency, ultimately reaching 18% STH with 10 µg Pt/cm² HER catalyst loading and an Ir-free anode in acidic media. These findings show that device cost can be decreased without compromising, or even with improvement, on performance parameters in PECs.