Atomic layer deposition of tungsten oxide thin films using bis(t-butylimido)-bis(dimethylamido)tungsten is investigated using various oxygen precursors. Significant amounts of unreacted nitrogen originating from the tungsten precursor are found in films deposited thermally using conventional oxygen sources like water, oxygen, and hydrogen peroxide. This problem is remedied using nitrogen dioxide as the oxygen source. Tungsten oxide films deposited using this rarely utilized precursor are shown to have minimal nitrogen content, an enhanced deposition rate, and a WO3 stoichiometry. The electrochemical and photothermal properties of films deposited using nitrogen dioxide are shown to be superior to films deposited using the other oxygen precursors.