In the present work, we report on a facile and effective approach to significantly enhance the photoelectrochemical activity of WO3. WO3 nanoflakes with hierarchical architecture prepared with a two-step hydrothermal method exhibits a significant enhancement of photocurrent density by a factor of 1.3 as compared with the pristine counterpart. The improved photoelectrochemical activity could be attributed to the enhanced light-harvesting capability induced by multiple light scattering and better interfacial charge transfer properties by facilitating the exposure of active sites benefited from the hierarchical architecture. An integration of the hierarchical WO3 electrode with a single-junction perovskite solar cell gives a solar energy conversion efficiency of 1.30% without external bias. (C) 2016 Elsevier Ltd. All rights reserved.