Structural tuning of ancillary chelate in tri-carboxyterpyridine Ru(ii) sensitizers for dye sensitized solar cells

Abstract

Three distinct classes of ancillary chelates, namely: 2-(3-trifluoromethylpyrazol-5-yl)-6-(3-trifluoromethylphenyl)pyridine (L3, H₂pzppy), 4-(3-trifluoromethylpyrazol-5-yl)-2-(3-trifluoromethyl)phenylpyrimidine (L5, H₂pzppm) and 4-(6-(3-trifluoromethylpyrazol-5-yl)pyridin-2-yl)-2-trifluoromethylpyrimidine (L6, H₂pzpypm), which showed an identical skeletal topology, but with the more electronegative nitrogen atom replacing the isoelectronic methine group at the selected skeletal position, were obtained to investigate the photophysical and electrochemical properties and hence the associated Ru(II) sensitizers based DSCs. To increase the optical absorptivity we also strategically added thiophene (thienyl) or 3,4-ethylenedioxythiophene (EDOT) appendages to L6, for boosting the short-circuit photocurrent (J_SC) and the overall efficiency (η) of the fabricated DSC devices. Under AM 1.5G illumination, the best sensitizer showed performance data of J_SC = 18.11 mA cm⁻², V_OC = 0.66 V, FF = 0.729 and η = 8.72%, and a good cell stability at 60 °C for 1000 hours, being only decreased by ∼5% in the η value.