Tungsten trioxide (WO3) films were prepared by a solution-based method using ammonium metatungstate as the precursor and polyethylene glycol as the structure-directing agent. With the measurements of thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and ultraviolet and visible absorption spectroscopy, the effect of substrates and temperature on the crystal structure and crystalline formation of WO3 was investigated. The results show that the WO3 films were crystallized by sintering at over 400 degrees C, and the films prepared on fluorine tin oxide glass substrates were distorted cubic in crystalline phase. However, a monoclinic crystal was formed by coating films on graphite and quartz glass substrates. Photoelectrochemical activity was evaluated under visible light irradiation. The WO3 electrode calcined at 450 degrees C exhibited a photocurrent density of up to 2.7 mA/cm(2) at 1.4 V (vs. RHE) under incident 100 mW/cm(2) 500W Xe lamp and donor carrier density N-D = 2.44 x 10(22) cm(-3) in 0.5 M H2SO4 electrolyte. The photoanode was stable up to 90 min, and the photocurrent decreased 39% with continuous gas evolution. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.