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Three new isomeric 1,1'-bis-(diphenylphosphino)ferrocene (dppf) appended nickel(II) dithiolates o-NiL, m-NiL and p-NiL (2-cyano-2-(2-methoxyphenyl)ethene-1,1-dithiolate (o-L), disodium 2-cyano-2-(3-methoxyphenyl)ethene-1,1-dithiolate (m-L) and disodium 2-cyano-2-(4-methoxyphenyl)ethene-1,1-dithiolate (p-L)) have been synthesized and characterized. The single X-ray analyses revealed that in all three complexes, nickel(II) adopts distorted square planar geometry arising because of the bidentate chelating coordination of two sulfur centers of dithiolate ligand and two phosphorus centers of dppf co-ligand. The distortion in geometry is arising because of the strained four membered NiS2C chelate ring formed by the dithiolate ligand as well as small variation in Ni-S and Ni-P bond lengths. The weak interactions existing in these newly synthesized sensitizers have been addressed with the help of Hirshfeld surface analysis. The electronic absorption spectra of all three compounds display absorption bands between ~400-500 nm and ~500-600 nm arising due to d-d transition of ferrocene and Ni(II), respectively. These compounds have been used as photo-sensitizers in dye sensitized solar cells (DSSCs). The experiments revealed that amongst all three sensitizer based DSSC set-ups, the assembly fabricated using p-NiL exhibited best photovoltaic performance due to stronger electronic coupling between the sensitizer and the semiconductor resulting in enhanced electron injection with 3.40 % efficiency (η) with short circuit current (Jsc) 7.10 mA.cm-2, open circuit voltage (Voc) -0.748 V and incident photon to current conversion efficiency of 63%. Also, the ageing experiment for the DSSC cell set-up fabricated using p-NiL revealed that after 700 h the set-up retained 93% of its efficiency that indicates that such class of molecular system can be used as apt sensitizers for DSSC fabrication.
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