Triple-Cation Perovskite Photoanodes for Solar Water Splitting: From Photovoltaic-Assisted to Immersed Photoelectrochemical Operation

Mixed-halide perovskite solar cells with the composition Cs0.1(MA0.17FA0.83)0.9Pb(I0.83Br0.17)3 were fabricated obtaining solar cells as glass/ITO/SnO2/triple cation perovskite/HTL/Au, subsequently used as photoanodes for efficient solar-driven water splitting by applying commercial catalytic nickel foils onto the Au back-contact pads of devices. To enable operation under alkaline media the de-vices were encapsulated using commercial PET–EVA multilayer films, providing a ro-bust barrier while leaving the Ni foils exposed as the electrochemically active interface. Two operating configurations were investigated and compared: (i) an outside configu-ration, where the perovskite solar cell powered an external electrochemical cell, and (ii) an immersed configuration, in which the encapsulated device was directly integrated into the electrolyte. In particular, the oxygen evolution reaction onset shifted from ~1.32 V vs RHE, when the Ni electrode was not powered by the perovskite absorber, to ~0.34 V vs RHE when the perovskite device powered the nickel foil for both immersed and outside configurations. The IS device achieved a maximum Applied Bias Photon-to-Current Ef-ficiency of ~20% under AM 1.5G illumination (100 mW cm⁻²), among the highest reported for perovskite-based photoanodes.