Water-splitting devices and methods for manufacturing water-splitting devices or solar cells is disclosed. The method seeks to provide a relatively high-volume, low-cost mass-production method. In one example, the method facilitates simultaneous co-assembly of one or more sub-units and two or more polymer films or sheets to form a water-splitting device. According to another aspect, there is provided an improved water-splitting device. In one example form, there is provided a water-splitting device which includes a first electrode for producing oxygen gas and a second electrode for producing hydrogen gas from water. The first electrode and the second electrode are positioned between a first outer polymer layer and a second outer polymer layer, and at least one spacer layer is positioned between the first outer polymer layer and the second outer polymer layer.