Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO(2) Photoanode

By simple soaking titanium dioxide (TiO(2)) films in an aqueous Na(2)S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (V(oc)) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV–visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na(2)S modification led to the formation of anions on the TiO(2) surface, and thereby shifted the conduction band edge of TiO(2) in the negative (upward) direction, inducing an increase of 29 mV in the V(oc). It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.