Electrochemical synthesis of cuprous oxide on highly conducting metal micro-pillar arrays for water splitting

•The metal micro-pillar arrays were synthesized by Ni electroless deposition.•The Cu2O absorber layer was electrodeposited on the Ni micro-pillar arrays.•The micro-pillar arrays decreased minority carrier diffusion length.•The photocurrent of the micro-pillar array was two times larger that of the plate.

Three-dimensional (3D) metal/cuprous oxide (Cu2O) micro-pillar arrays were fabricated by electroless deposition of Ni on Si micro-pillars followed by the electrochemical deposition of Cu2O on the metal micro-pillars. The metal micro-pillars with heights of 16 μm and diameters of 1–1.5 μm showed low reflectance and conductance values similar to Cu2O plates, indicating that the 3D metal/Cu2O micro-pillars are good current collectors. The photocurrent of the 3D metal/Cu2O micro-pillar arrays was more than twice that of the Cu2O plates. This high photocurrent for the 3D metal/Cu2O micro-pillar results from its large surface area, long optical absorption depth (micro-pillar length) and short carrier diffusion length (thin Cu2O absorber).