Expanded light-absorption and efficient charge-separation: bilayered thin film nano-hetero-structures, CuO/Cu–ZnO, make efficient photoanode in photoelectrochemical water splitting

High efficiency photoelectrochemical water splitting is achieved, using uniquely evolved bi-layered nano-hetero-structured (BNHS) thin films, CuO/Cu–ZnO, grown over ITO (In:SnO 2 ) glass substrate by spray-pyrolysis and sol–gel spin-coating. Films were characterized by X-ray diffractometry, scanning electron microscopy, atomic force microscopy, UV–visible spectrometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Significant gain in photocurrent and applied bias photon-to-current efficiency, with 3% Cu incorporated BNHS films yielding maximum photocurrent ~ 2.98 mA cm −2 , is attributable to favourable changes in material microstructure and electrical properties. CuO nanparticles existing as dispersed phase in ZnO overlayer and tendering a possible mechanism for the transfer of photogenerated holes from the underneath CuO layer to electrolyte is a highlighting proposition of this report. Graphic abstract