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Structure–property relationship of hetero-aromatic-electron-donor antennas of polypyridyl Ru (II) complexes for high efficiency dye-sensitized solar cells



Three novel heteroleptic amphiphilic polypyridyl Ru-complexes, coded MH08–10, with hetero-aromatic electron-donor ancillary ligands containing N-benzylcarbazole (MH08), dibenzofurane (MH09) and benzothiophene moieties (MH10) were synthesized to study the influence of different heterocyclic electron donors on the interrelationship of photophysical and electrochemical properties, and device performances for dye-sensitized solar cells (DSSCs). MH08 showed a remarkably high molar extinction coefficient of 27,650 M−1cm−1. MH08–TBA was synthesized from MH08 by converted one COOH group into −COO−+N(C4H9)4 to investigate the effect of deprotonating one carboxylic group on the Fermi level and electron injection. When compared under the same experimental device conditions using 0.3M t-butylpyridine (TBP), the short-circuit photocurrent density (JSC) and total conversion efficiency (%η) of MH08–10 were MH08>MH09>MH10. The differences in %η and JSC of MH08–10 were ascribed to the conjugation length coupled with the electron donation and hole-transport strength of the ancillary ligands, which were in the following order N-benzylcarbazole>dibenzofurane>benzothiophene. Moreover, MH08–TBA showed JSC of 19.56 mAcm−2 and %η of 9.76% compared to 17.16 mAcm−2 and 9.12% of the benchmark dye N719. The superior performance of MH08–TBA was attributed to its better light harvesting and enhanced incident-photon-to-current efficiency (IPCE) conversion. DFT/TD-DFT calculations utilizing the energy functional B3LYP and the full-electron basis set DGDZVP were performed to calculate HOMO and LUMO energies, vertical electronic excitations, lowest singlet-singlet electronic transitions (E0-0), and excited state oxidation potentials. Excellent agreement was found between the experimental results and calculated data. Copyright © 2013 John Wiley & Sons, Ltd.