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 ligandIMA5was synthesized for dye-sensitized solar cells (DSSCs). The performance of these DSSCs has been enhancedviadi-anchoring metal-free organic sensitizers, denotedIMA1-4, with structural motif A-pi-D-pi-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 thatIMA3had the best DSSC performance (eta= 2.41%). In addition,IMA1-4was co-sensitized in conjunction with the newly synthesizedIMA5complex to enhance light harvesting across expanded spectral regions and thus improve efficiency. The solar cells co-sensitized withIMA2,IMA3andIMA4exhibited improved efficiency (eta) of 6.25, 6.19 and 5.83%, respectively, which outperformed the device employingIMA5alone (eta= 5.54%) owing to the improvement in the loading ofIMA2,IMA3andIMA4in the presence ofIMA5on the surface of the TiO(2)nanoparticles, and charge recombination was suppressed.