The yield and mobility of charge carriers in smooth and nanoporous TiO2 films

The product of the quantum yield, eta, and the mobility, Sigma mu, of charg e carriers formed on flash-photolysis (7 ns, 308 nm) of thin films of TiO2 has been measured as a function of intensity from ca. 0.5 to 2000 mu J/cm(2 ) using the time-resolved microwave conductivity technique (TRMC). For a sm ooth, 78 nm film formed by electron-beam evaporation (EBE) eta Sigma mu was 1.9 cm(2)/Vs for the lowest intensity used and remained close to constant up to approximately 10 mu J/cm(2). Above this intensity eta Sigma mu decrea sed gradually to 0.35 m(2)/Vs at 2000 mu J/cm(2). For nanoporous films of D egussa P25 and Solaronix TiO2 eta Sigma mu increased with increasing intens ity up to approximately 10 mu J/cm(2) above which it decreased gradually. T he maximum values attained (0.08 and 0.3 cm(2)/Vs respectively) were more t han an order of magnitude lower than for the EBE film.