Optimizing the photovoltaic performance of thiocyanate-free ruthenium photosensitizers by structural modification of C^N cyclometalating ligand in dye-sensitized solar cells

Five new thiocyanate-free ruthenium(II) complexes with different electron-donating functionalized cyclometalating ligands C^N were synthesized, characterized and applied as photosensitizers in dye-sensitized solar cells (DSSCs). Their photophysical, electrochemical, thermal and photovoltaic properties have been investigated and density functional theory (DFT) calculations have been carried out on these dyes. These dyes exhibit good thermal stability with the onset decomposition temperature at 5% weight-loss (Td) of around 330 °C. The DSSC device using the Ru(II) dye with the 9-tolylcarbazole chromophore exhibited the highest power conversion efficiency (η) up to 3.39%, with a short-circuit photocurrent density (Jsc) of 8.06 mA cm-2, an open-circuit photovoltage (Voc) of 0.62 V and a high fill factor (ff) of 0.68 under illumination of an AM 1.5 solar cell simulator.