A photoelectrochemical (PEC) water-splitting device integrates a photovoltaic cell and electrocatalysts into a single device to produce hydrogen fuel from water using solar irradiance. The major driving force behind PEC research is that it can potentially be a cost-efficient way to produce hydrogen in a renewable way, however, current PEC devices for hydrogen production are not economically viable yet. This review provides comprehensive discussions on the major challenges on practical solar hydrogen production by PEC from the standpoint of device structure and light absorber materials. We started by systematically classifying PEC device structures based on the electrical junctions on the light absorber materials. Based on the classification scheme, we showed that the choices of a device structure and light absorber materials are cross-linked in current PEC studies and affects electron/ion transport in a PEC device. The correlation between the device structure and materials underlines the necessity of reviewing the light absorber materials for the top and bottom cells in a tandem PEC device as a whole. We categorize the light absorber materials based on their crustal abundance because it is a major factor that determines device structure and scalability in TW-scale, and discuss their influence on the efficiency, stability, and scalability of a PEC water-splitting system.