Effect of morphology on electron drift mobility in porousTiO2

摘要

Porous titanium dioxide is an attractive material for solar cell application on account of itsstability, electron transport properties, and the possibilities for controlling surface morphology as well asfor its ease of fabrication and low cost. NanostructuredTiO2has been intensively studied for applicationsto dye sensitised solar cells. The performance of the titanium dioxide based solar cells is influenced, amongother factors, by the electron mobility of the porous titanium dioxide. Different fabrication processes forporous titanium films result in different film morphology, which in turn affects the electron transport. Wehave employed three different techniques namely, electrostatic spray assisted vapour deposition (ESAVD),D.C. reactive sputtering, and doctor blading of sol-gel dispersions to deposit thinTiO2films onto indium tinoxide (ITO) coated glass substrates. All these films exhibited only the anatase phase as confirmed by X-raydiffraction analysis. Using the time-of-flight technique, the electron drift mobility in the porousTiO2films was measured. The results show that in the low field region (<55,000 Vcm?1) the mobility, in all the films, were in the range of10?7to10?6cm2Vs?1. The drift mobility in the films prepared by reactive sputteringwas consistently higher than in the films prepared by the two other techniques. Sputter deposited films hadlower porosity (～10% and 36% for normal-, and oblique (60°)-angle deposited films) compared to～50% for films deposited by the two other techniques. The relationship between the drift mobility and film morphologyis discussed with the aid of scanning electron microscopy studies.