PHOTOCURRENT LOSSES IN NANOCRYSTALLINE NANOPOROUS TIO2 ELECTRODES DUETO ELECTROCHEMICALLY ACTIVE SPECIES IN THE ELECTROLYTE/

The photoelectrochemical properties of nanostructured highly porous Ti O2 electrodes with different thicknesses (2 to 38 mu m) were investiga ted. The effects of electron accepters, such as oxygen and iodine, in the electrolyte were studied by action spectra measurements. The chang es due to oxygen and iodine were explained by increased loss oi photog enerated electrons over the nanostructured semiconductor electrolyte i nterface during the transport of the electrons to the back contact, pH had a pronounced effect on the spectral distribution. At pH 1.2 the p hotoresponse is high and independent of the presence oxygen. Front sid e illumination of a 38 mu m thick electrode measured in a stirred nitr ogen purged solution converts amazingly 10% of the photons to current indicating that the transport of electrons in these films can be extre mely good when the electrolyte composition is favorable. The efficienc y for back side illumination increases with film thickness, even up to 38 mu m, in stirred solutions. The investigation shows that one must consider the electrode and the electrolyte in the cavities as an integ rated nanostructured system. It also illustrates important parameters in three-electrode measurements on these kinds of systems.