Multiple heterojunction made of CuO nanocrystals building on ZnO scaffold buffered by an In2O3 inter layer is fabricated through simple wet chemistry. Scanning and transmission electron microscopy reveal this CuO/In2O3/ZnO heterojunction forming multi-core-shell nanostructure. X-ray photoelectron spectroscopy is performed to analyze the chemical compositions. Such system is further employed in sunlight-driven photoelectrochemical water splitting, wherein Mott-Schottky analysis demonstrates its flat-band potential negatively shifted. This originates from the lower electron affinity of CuO compared to that of ZnO, favoring photocurrent generation at early onset potential. More importantly, the entire gamut of visible-light is harnessed by CuO, as manifested in the photocurrent action spectrum. Last but not least, the charge-separation is promoted at the In2O3 interface, as reflected in the impedance measurement. The synergistic effect endows the CuO/In2O3/ZnO photoelectrode with the highest photocurrent of 1.22 mA.cm(-2) (at similar to 1.6 V vs. RHE) that outperforms those of the CuO/ZnO and ZnO photoanodes, respectively. (C) 2019 Elsevier Inc. All rights reserved.