Impact of substituent's position on the DSSC performances of new 1,1′-bis-(diphenylphosphino)ferrocene appended nickel(ii) methoxy cyanodithiolates

Three new isomeric 1,1′-bis-(diphenylphosphino)ferrocene (dppf) appended nickel(II) dithiolates o-NiL, m-NiL and p-NiL (disodium 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 a distorted square planar geometry arising from the bidentate chelating coordination of two sulfur centers of the dithiolate ligand and two phosphorus centers of the dppf co-ligand. The distortion in geometry is because of the strained four membered NiS2C chelate ring formed from 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 from the 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 the 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 a short circuit current (Jsc) of 7.10 mA cm−2, open circuit voltage (Voc) of −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 which indicates that such a type of molecular system can be used as an apt sensitizer for DSSC fabrication.