Over 17% efficiency stand-alone solar water splitting enabled by perovskite-silicon tandem absorbers

Realizing solar-to-hydrogen (STH) efficiencies close to 20% using low-cost semiconductors remains a major step toward accomplishing the practical viability of photoelectrochemical (PEC) hydrogen generation technologies. Dual-absorber tandem cells combining inexpensive semiconductors are a promising strategy to achieve high STH efficiencies at a reasonable cost. Here, a perovskite photovoltaic biased silicon (Si) photoelectrode is demonstrated for highly efficient stand-alone solar water splitting. A p⁺nn⁺ -Si/Ti/Pt photocathode is shown to present a remarkable photon-to-current efficiency of 14.1% under biased condition and stability over three days under continuous illumination. Upon pairing with a semitransparent mixed perovskite solar cell of an appropriate bandgap with state-of-the-art performance, an unprecedented 17.6% STH efficiency is achieved for self-driven solar water splitting. Modeling and analysis of the dual-absorber PEC system reveal that further work into replacing the noble-metal catalyst materials with earth-abundant elements and improvement of perovskite fill factor will pave the way for the realization of a low-cost high-efficiency PEC system.