  We present the results of XPS measurements (core levels and valence bands) of
solution processed TiOx thin films prepared from titanium butoxide (C16H36O4Ti)
diluted in isopropanol which is a common sol-gel route for fabricating TiOx
electron selective contacts for ITO/TiOx inverted organic photovoltaics bottom
electrodes. XPS Ti 2p and valence band spectra show the presence of additional
features which are absent in spectra of titanium butoxide deposited on Si and
are attributed to appearance of Ti^{3+} valence states in ITO/TiOx. This
conclusion is confirmed by density functional theory electronic structure
calculations of stoichiometric TiO2 and oxygen deficient TiO_{2-1/8}. XPS C 1s
measurements show the formation of C-O and O-C=O bonds which evidence the
presence of residual carbon which can draw oxygen from the film network and
induce the formation of fraction of Ti3+ states in TiOx films.
