Effect of Different Dye Baths and Dye-Structures on the Performance of Dye-Sensitized Solar Cells Based on Triphenylamine Dyes

Triphenylamine dyes were designed and synthesized as photosensitizers for dye-sensitized solar cells (DSSCs). Different substituted phenylene units, 2,2';5',2''-ter-thiophene (TT) and dithieno[3,2-b;2',3'-d]thiophene (DTT) serve as the π-spacers - the electron acceptors use cyanoacrylic acid or rhodanine-3-acetic acid units. A detailed study on the relation between the dye structure, and photophys., photoelectrochem. properties and performance of DSSCs is described here. By substituting the phenylene group with electron-withdrawing units as π-spacers or replacing the cyanoacrylic acid with rhodanine-3-acetic acid units as electron acceptors, bathochromic shift of absorption spectra is achieved. Significant differences in the redox potential of these dyes are due to small structure changes. The different dye baths for semiconductor sensitization have a crucial effect on the performance of the DSSCs due to the different absorbed amt., absorption spectra and binding modes of anchored dyes on the TiO2 surface in various solvents. From optimized dye bath and mol. structure, TPC1 shows a prominent solar-to-electricity conversion efficiency (η), 5.33% (JSC = 9.7 mA/cm2, VOC = 760 mV, ff = 0.72), under simulated AM 1.5 G irradn. (100 mW/cm2). DFT showed the electron distribution and the intramol. charge transfer (HOMO→LUMO) of the dyes. From the calcn. results of the selected dyes, the authors can also find the cyanoacrylic acid unit better than the rhodanine-3-acetic acid unit as electron acceptor. Also, the electron-withdrawing groups on phenylene units as π-spacers show the neg. effect on the performance of the org. DSSCs.