Efficiency enhancement of ruthenium-based DSSCs employing A-π-D-π-A organic Co-sensitizers

A new bipyridyl Ru(ii) sensitizer incorporating triphenylamine and the 3,4-ethylenedioxythiophene (EDOT) ancillary ligand IMA5 was synthesized for dye-sensitized solar cells (DSSCs). The performance of these DSSCs has been enhanced via di-anchoring metal-free organic sensitizers, denoted IMA1-4, with structural motif A-π-D-π-A and incorporating phenyl-dibenzothiophene-phenyl (Ph-DBT-Ph) as the main building block but with different anchoring groups (A). These new organic sensitizers were well-characterized and used as efficient co-sensitizers. Their photophysical, electrochemical and photovoltaic properties were studied. Furthermore, molecular modeling studies using DFT calculations were used to investigate their suitability as effective sensitizers/co-sensitizers. The molecular orbital isodensity showed distinguishable delocalization of the intramolecular charge in the DBT moiety. The photovoltaic characterization showed that IMA3 had the best DSSC performance (η = 2.41%). In addition, IMA1-4 was co-sensitized in conjunction with the newly synthesized IMA5 complex to enhance light harvesting across expanded spectral regions and thus improve efficiency. The solar cells co-sensitized with IMA2, IMA3 and IMA4 exhibited improved efficiency (η) of 6.25, 6.19 and 5.83%, respectively, which outperformed the device employing IMA5 alone (η = 5.54%) owing to the improvement in the loading of IMA2, IMA3 and IMA4 in the presence of IMA5 on the surface of the TiO₂ nanoparticles, and charge recombination was suppressed.