Tungsten oxide-coated copper gallium selenide sustains long-term solar hydrogen evolution

This work demonstrates that ultrathin (4 nm) tungsten oxide (WO₃) coatings on copper gallium selenide (CuGa₃Se₅) photocathodes have the potential for long-term solar hydrogen evolution. With a combination of a robust 1.84 eV CuGa₃Se₅ absorber layer, a WO₃ protective coating, and a Pt catalyst, we obtain a new durability milestone for any non-silicon photoelectrochemical hydrogen-producing device by passing 21 490 C cm⁻² of charge across six weeks of continuously-illuminated chronoamperometric testing under applied bias.