The deficiencies in the separating photogenerated electrons/holes in the bulk and driving them across the interface of semiconductor/electrolyte are the major issues that limit the photoelectrochemical (PEC) performance of hematite (alpha-Fe2O3) photoelectrodes. In this work, a Z-scheme planar heterostructure of n-Si and alpha-Fe2O3 was designed and constructed by a facial ion-beam assisted deposition technique with the best match of the optical absorption depth, the film thickness and the space charge region thickness. A thin ITO layer (similar to 10 nm) was sandwiched in-between in order to achieve the optimal carrier separation capacity, and the IrOx cocatalysts were introduced to improve the surface reaction kinetics. The results demonstrate a significant improvement of alpha-Fe2O3 PEC performance: a photocurrent density was improved to 1.987 mA cm(-2) (1.23 V vs. RHE), similar to 100 times larger than that of bare alpha-Fe2O3, whereas the onset potential was dropped by 0.57 V over unmodified alpha-Fe2O3, due to the enhanced photovoltage by n-Si and the improved surface reaction kinetics. This work advances planar alpha-Fe2O3-based photocatalytic cells to a new performance record for water splitting. (C) 2019 Elsevier Inc. All rights reserved.