Abstract
We report on a new series of Ru(II) sensitizers TFRS-61 -66 suited for high performance dye sensitized solar cells (DSCs). The molecular design incorporates novel dianionic bipyrazolate or bitriazolate ancillaries to replace the dual thiocyanates in N3 (or N719) with the aim of improving device stability. These newly designed dianionic biazolate ligands make feasible the fine-tuning of the ground state oxidation potential. This, together with the synergistic incorporation of electron-donating thiophene or thiophene-containing appendages to one bipyridine for harvesting the spectral coverage, leads to the achievement of DSC with a prominent JSC of 17.4 mA∙cm-2 and hence a high photon conversion efficiency of 9.6% using TFRS-63, which is comparable with the N3 control device (9.5% in this study) but with leaping improvement in device stability. Comprehensive electrochemical impedance, charge extraction, transient photovoltage and transient absorption spectroscopy measurements have been carried out to gain insight into the fundamental of these new dyes and the associated device properties. These biazolate substituted Ru(II) sensitizers add another dimension for replacing thiocyanate containing Ru(II) sensitizers en route to high performance DSC.