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Two novel heteroleptic brominated-TPA-stilbazole based Ru (II)-sensitizers denoted as SD-11 and SD-11 mono were designed, synthesized and characterized for dye-sensitized solar cells (DSCs) in comparison to benchmarked dye N719. The molecular structures of SD-11 and SD-11 mono were confirmed using FTIR, 1 H-NMR and mass spectrometry. The aim was to systematically study the effect of mono (SD-11 mono) versus bis-brominated-TPA moiety (SD-11) on molar absorptivity, ground and excited state oxidation potentials, light harvesting efficiency (LHE), incident-photon-to-current conversion efficiency (IPCE), short-circuit photocurrent density ( J sc), and total solar-to-electric conversion efficiency ( η ) for DSCs. Optical results revealed that SD-11 and SD-11 mono have higher molar extinction coefficients, narrower HOMO−LUMO gaps compared to N719. Hence, it was found that SD-11 exhibited remarkably greater J sc than SD-11 mono and interestingly showed comparable extinction coefficients. However, in optimized conditions, SD-11 showed a higher J sc of 22.1 mA cm −2 , V oc of 0.68 V with (% η) of 8.7 compared to J sc of 14.4 mA cm −2 , V oc of 0.63 V and with (% η) of 5.8 for SD-11 mono whereas N719 attained a J sc of 15.9 mA cm −2 , V oc of 0.74 V with (% η) of 7.6 under the same experimental device conditions. It was concluded that SD-11 outperformed SD-11 mono in photovoltaic performance when anchored on TiO 2 , owing to better light-harvesting ability. These results clearly demonstrated that the enhancement of the photovoltaic performance in SD-11 can be attributed to the presence of more number of –Br group. [ABSTRACT FROM AUTHOR]

Structure-property relationships of four novel bipyridyl Ru(II) complexes, denoted as SD-22, SD-24, SD-26 and SD-28, are reported herein. The molecular structures of all four photosensitizers were confirmed using FT-IR, 1H NMR and mass spectrometry. Photovoltaic characteristics of the photosensitizers were evaluated under 1.5 a.m. standard illumination condition, in presence of deoxycholic acid as co-adsorbent, and subsequently compared to the performance of the benchmark, Z907. SD-22 showed an IPCE of 52% and 50% at 440 nm and 550 nm, respectively, a short-circuit photocurrent density (J SC) of 17.37 mA cm−2, open-circuit photovoltage (V OC) of 0.63 V and fill factor (FF) of 0.66, producing an overall conversion efficiency (η) of 7.31%, which outperformed Z907 (7.02%) under the same experimental device conditions. The η of the other photosensitizers is in the following order: SD-22 > SD-28 > SD-26 > SD-24. Photosensitizer SD-22 has N, N′ -dialkyl group attached to a benzene ring while SD-24 has N,N′-dialkyl without a benzene ring. The extended conjugation in SD-22 translated into higher overall solar-to-electric conversion efficiency. Substitution of dialkylamino-based ancillary ligands of Ru(II) dyes SD-26 and SD-28 with –OCH 3 and –OC 6 H 13 also demonstrated that the photovoltaic performance of polypyridyl ruthenium photosensitizers is a function of the donating power of ancillary ligands as well as the steric effect of alkoxy auxochromes at – ortho position. • Structure-property relationship of four bipyridyl Ru(II) complexes with N , N′ -diethyl group in ancillary ligand was studied. • Highlights the effect of extended conjugation on the photocurrent and photovoltage in DSSC. • SD-22 outperformed the rest of the dyes in photovoltaic performance due to better light-harvesting ability. • Enhancement of the photovoltaic performance in SD-22 is ascribed to the presence of aromatic ring and smaller alkyl chains. • Molecular modulations of electron donating N , N′ -diethyl based Ru(II) dyes was presented to further analyze the properties. [ABSTRACT FROM AUTHOR]