Direct solar to hydrogen conversion enabled by silicon photocathodes with carrier selective passivated contacts

Direct solar hydrogen generation using systems based on low-cost materials is a potential pathway to achieve low-cost renewable hydrogen at large scale, and photoelectrodes that leverage well-established silicon (Si) technology are a particularly promising approach. Two key requirements to achieve highly efficient and stable Si photoelectrodes are electronic passivation to reduce recombination losses at the Si/catalyst interface, and chemical protection of Si from corrosion in the alkaline electrolyte. In this work, Si photocathodes are fabricated by employing a carrier selective passivation layer consisting of an ultrathin SiOx (∼1.4 nm) capped with n+ polycrystalline Si (∼70 nm), and a compact NiMo/Ni bilayer catalyst. The Si photocathodes integrated with Earth abundant catalyst and state-of-art charge selective passivation layer achieve an applied bias to photon conversion efficiency of 10.5%, and high stability above 60 hours. Importantly, the NiMo/Ni catalyst is developed using the industry-relevant sputter deposition method presenting vertically aligned, rod-like nanostructures with a low overpotential of 89 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER). Finally, a remarkable overall unassisted water splitting efficiency of 17% is achieved for an all-low-cost materials-based system, by combining the Si photocathode with a high bandgap perovskite PV top cell in tandem configuration, and a high-performance NiFe electrode for oxygen evolution reaction.