Efficiency improvement of DSSC photoanode by scandium doping of mesoporous titania beads

Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (?650 nm) and rice-grain-shaped at the nanoscopic level (?20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m2 g–1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with ScTi substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0–1.0 at. % of Sc, the flat band energy changes from ?4.15 to ?4.07 eV, whereas the band gap height increases by 0.03 eV. The presence of Sc modifies heavily the cathodoluminescence spectrum of anatase at the lowest concentration too. Several DSSCs with photoanodes at different Sc doping were tested both under solar simulator and in the dark. The maximum efficiency of 9.6% was found at 0.2 at. % of Sc in anatase that is 6.7% higher with respect to the DSSCs with pure anatase.