Conversion Efficiency Versus Sensitizer for Electrospun TiO(2) Nanorod Electrodes in Dye-sensitized Solar Cells

The electrochemical and optical properties of three indoline dyes, namely C(35)H(28)N(2)O(2) (D131), C(37)H(30)N(2)O(3)S(2) (D102), and C(42)H(35)N(3)O(4)S(3) (D149), were studied and compared with that of the N3 dye. D131 has the largest bandgap and lowest unoccupied molecular orbital (LUMO) energies compared to the other dyes. A size-dependent variation in the absorptivity of the indoline dyes was observed-the absorptivity increased with increase in the molecular size. The dyes were anchored onto TiO(2) nanorods. The TiO(2) nanorods were obtained by electrospinning a polymeric solution containing titanium isopropoxide and polyvinylpyrrolidone and subsequent sintering of the as-spun composite fibers. Absorption spectral measurements of the dye-anchored TiO(2) showed blue shifts in the excitonic transition of the indoline dyes, the magnitude of which increased with decrease in the molecular size. Dye-sensitized solar cells (DSSCs) were fabricated using the indoline dyes, TiO(2) nanorods, and iodide/triiodide electrolyte. The D131 dye showed comparable energy conversion efficiency (η) to that of the N3 dye. A systematic change in the short circuit current density (J(SC)) and η of the indoline DSSCs was observed. The observed variation in J(C) is most likely originated from the difference in the electronic coupling strengths between the dye and the TiO(2).