Tunability of the Band Energetics of Nanostructured SrTiO₃ Electrodes for Dye-Sensitized Solar Cells

The flat band edges ( E fb ) of nanostructured SrTiO 3 electrodes have been determined in propionitrile (PN), acetylacetone (Acac), and PN/Acac with spectroelectrochemistry measurements. Specifically, a very negative E fb was measured when only tetrabutylammonium perchloride (TBAP) was used as supporting electrolyte, while addition of Li + ions shifts E fb positively. The trap state distribution was investigated by the measurements of time-resolved current. The total trap state densities of 5.51 × 10 16, 2.80 × 10 16, and 1.83 × 10 16 cm −2 were determined in PN, PN/Acac, and Acac (all containing 0.2 mol·L −1 TBAP), respectively, with trap distribution maximum located at −2.4, −1.6, and −1.5 V. The addition of Li + also reduced the trap state densities, and the total trap state densities were calculated to be 4.19 × 10 16, 2.38 × 10 16, and 1.19 × 10 16 cm −2 in PN, PN/Acac, and Acac (all containing 0.2 mol·L −1 TBAP and 0.5 mol·L −1 LiClO 4 ), respectively. Finally the nanostructured SrTiO 3 electrode was sensitized with dye N3 and its photovoltage−photocurrent curves were measured in three electrolytes with PN, PN/Acac, and Acac as solvents, respectively. The N3-sensitized SrTiO 3 showed the highest open-circuit voltage ( V oc ) and short-circuit current density ( J sc ) in Acac, in good agreement with the electrochemical measurements that the nanostructured SrTiO 3 electrode has the flat band edge well matching with the excited state of N3 and the smallest trap state densities in Acac.