Photoeffects at Polycrystalline Tin Oxide Electrodes

The electrochemical behavior of thin‐film polycrystalline tin oxide electrodes under subbandgap energy photoexcitation has been investigated. Photocurrents were dependent on the intensity of the light, wavelength, and the applied potential. The photocurrent spectrum showed a sharp decrease near the bandgap energy. This photocurrent is due to the oxidation of water in the electrolyte by holes at the permitted energy levels in the bandgap region. These energy states are formed by the presence of impurities, which are largely halides remaining from the preparation steps, grain boundaries, and adsorbed foreign molecules. A superficial hydrogen bonding interaction between oxide layers of and water molecules is proposed for the hydrated surface of tin oxide.