Interface engineering of the photoelectrochemical performance of Ni-oxide-coated n-Si photoanodes by atomic-layer deposition of ultrathin films of cobalt oxideElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ee01687h

Introduction of an ultrathin (2 nm) film of cobalt oxide (CoO x ) onto n-Si photoanodes prior to sputter-deposition of a thick multifunctional NiO x coating yields stable photoelectrodes with photocurrent-onset potentials of ∼−240 mV relative to the equilibrium potential for O 2 (g) evolution and current densities of ∼28 mA cm −2 at the equilibrium potential for water oxidation when in contact with 1.0 M KOH(aq) under 1 sun of simulated solar illumination. The photoelectrochemical performance of these electrodes was very close to the Shockley diode limit for moderately doped n-Si(100) photoelectrodes, and was comparable to that of typical protected Si photoanodes that contained np + buried homojunctions. Interfacial CoO x layers provide a route to stable, high-performance Si photoanodes for water splitting, without requiring np + homojunctions.