https://phys.org/news/2018-10-solar-cell-duty-renewable-energy.html > Finding a way out for electrons > Most water-splitting devices are made of a stack of light-absorbing materials. Depending on its makeup, each layer absorbs different parts or "wavelengths" of the solar spectrum, ranging from less-energetic wavelengths of infrared light to more-energetic wavelengths of visible or ultraviolet light.