Novel heteroleptic ruthenium sensitizers containing carbazole linked 4,5-diazafluorene ligand for dye sensitized solar cells

Abstract

Two novel heteroleptic ruthenium (II) sensitizers S1 and S2 containing an ancillary ligand 9,9-bis(9-ethylcarbazol-3-yl)-4,5-diazafluorene and 9,9-bis(9-phenylcarbazol-3-yl)-4,5-diazafluorene respectively, have been synthesized and characterized by 1H NMR, UV–Vis absorption spectroscopy, mass spectrometry, elemental analysis and cyclic voltammetry, and used as sensitizers in dye sensitized solar cells. The results show that for the two ruthenium sensitizers, the introduction of carbazole via sp3 hybridized C9 atom of the 4,5-diazafluorene unit produces significant changes in their optical absorption spectra and subsequently alters the intra-molecular charge transfer processes that influence the photovoltaic performance of the solar cell device. The power conversion efficiency of dye sensitized solar cells fabricated using sensitizers S1 and S2 are 0.36% and 0.42% respectively, while N719 exhibits 3.6% under the same device fabrication and measuring conditions.