New heteroleptic 1,2-bis(diphenylphosphino)ethane appended cobalt(iii) ferrocene dithiocarbamates as sensitizers in dye-sensitized solar cells (DSSCs)

Three new heteroleptic 1,2-bis(diphenylphosphino)ethane (dppe) appended Co(iii) ferrocene dithiocarbamate complexes with the formula [Co(dppe)(Fcdtc)]PF₆ ((Fcdtc = N-benzyl-N-methylferrocene dithiocarbamate (Co-FcBz), N-2-methylpyridyl-N-methylferrocene dithiocarbamate (Co-FcPy) and N-ethanol-N-methylferrocene dithiocarbamate (Co-FcEtOH); dppe = 1,2-bis(diphenylphosphino)ethane) have been synthesized and characterized by microanalyses, FTIR spectroscopy, electronic absorption spectroscopy and single crystal X-ray diffraction. Single crystal X-ray diffraction revealed that the geometry around Co(iii) in the Co-FcBz and Co-FcEtOH complex cations is distorted octahedral and satisfied by four sulfur atoms of two dithiocarbamate ligands and two phosphorus atoms of the dppe ligand. The weak interactions existing in Co-FcBz and Co-FcEtOH have been addressed with the help of Hirshfeld surface analysis. The electronic absorption spectra of all three compounds display bands in the regions of ∼400-500 nm and ∼500-750 nm which are due to the d-d transition of ferrocene and Co(iii), respectively. These compounds have been used as photo-sensitizers in dye-sensitized solar cells (DSSCs). Experiments revealed that amongst all three sensitizer-based DSSC set-ups, the assembly fabricated using Co-FcEtOH exhibited the best photovoltaic performance with 3.89% efficiency (η), a short circuit current (J_sc) of 9.15 mA cm⁻², an open circuit voltage (V_oc) of −0.680 V and an incident photon-to-current conversion efficiency of 49%. Also, the ageing experiment for the DSSC set-up fabricated using Co-FcEtOH revealed that after 100 h, the set-up retained 97% of its efficiency, which indicates that such a class of molecular systems can be used as apt sensitizers for DSSC fabrication.