Effect of different dye baths and dye-structures on the performance of dye-sensitized solar cells based on triphenylamine dyes

A series of triphenylamine dyes were designed and synthesized as photosensitizers for the application of organic dye-sensitized solar cells (DSSCs). Different substituted phenylene units, 2,2';5',2 ''-terthiophene (TT) and dithieno[3,2-b;2',3'-d]thiophene (DTT) serve as the pi-spacers, and the electron acceptors employ the cyanoacrylic acid or rhodanine-3-acetic acid units. Detailed investigation on the relationship between the dye structure, and photophysical, photoelectrochemical properties and performance of DSSCs is described here. By substituting the phenylene group with electron-withdrawing units as pi-spacers or replacing the cyanoacrylic acid with rhodanine-3-acetic acid units as electron acceptors, the bathochromic shift of absorption spectra are achieved. The significant differences in the redox potential of these dyes are also influenced by small structure changes. Furthermore, the different dye baths for semiconductor sensitization have a crucial effect on the performance of the DSSCs due to the different absorbed amount, absorption spectra and binding modes of anchored dyes on TiO2 surface in various solvents. On the basis of optimized dye bath and molecular structure, TPC1 shows a prominent solar-to-electricity conversion efficiency (eta), 5.33% (J(SC) = 9.7 mA.cm(-2), V-OC = 760 mV, ff = 0.72), under simulated AM 1.5G irradiation (100 mW.cm(-2)). Density functional theory has employed to study the electron distribution and the intramolecular charge transfer (HOMO -> LUMO) of the dyes. From the calculation results of the selected dyes, we can also find the cyanoacrylic acid unit is better than the rhodanine-3-acetic acid unit as electron acceptor. Also, the electron-withdrawing groups on phenylene units as pi-spacers show the negative effect on the performance of the organic DSSCs.