• G Rajkumar

      Articles written in Journal of Chemical Sciences

    • High spectral response heteroleptic ruthenium (II) complexes as sensitizers for dye sensitized solar cells

      M Chandrasekharam Ch Srinivasarao T Suresh M Anil Reddy M Raghavender G Rajkumar M Srinivasu P Yella Reddy

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      Heteroleptic ruthenium(II) bipyridyl complex, cis-Ru(II)(4,4'-bis(4-tert-butylstyryl)-2,2'-bipyridyl) (4,4'-dicarboxy-2,2'-bipyridyl) (NCS2) (H112) was synthesized and characterized by 1H-NMR, MASS, Spectrofluorometer and UV-Vis spectroscopes. The photo-voltaic performance of the sensitizer was evaluated in Dye Sensitized Solar Cell (DSSC) under irradiation of AM 1.5 G solar light and the photovoltaic characteristics were compared with those of reference cells of HRS1 and N719 fabricated under comparable conditions. Compared to N719, H112 sensitizer showed enhanced molar extinction coefficient and relatively better monochromatic incident photon-to-current conversion efficiency (IPCE) across the spectral range of 400 to 800 nm with solar energy-to-electrical conversion efficiency (𝜂) of 2.43% [open circuit photovoltage (VOC) = 0.631V, short-circuit photocurrent density (JSC) = 8.96 mA/cm2, fill factor (ff) = 0.430], while 𝜂 values of 2.51% (VOC = 0.651V, JSC = 9.41 mA/cm2, ff = 0.410) and 2.74% (VOC = 0.705 V, JSC = 8.62 mA/cm2, ff = 0.455) were obtained for HRS1 and N719 sensitized solar cells respectively. The introduction of 4,$4'$-bis(4-tert-butylstyryl) moieties on one of the bipyridine moieties of N719 complex shows higher light absorption abilities, IPCE and JSC.

    • Ruthenium(II)- bipyridyl with extended 𝜋-system: Improved thermo-stable sensitizer for efficient and long-term durable dye sensitized solar cells

      M Chandrasekharam G Rajkumar Ch Srinivasa Rao T Suresh P Y Reddy Y Soujanya

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      A new extended thermo-stable high molar extinction coefficient bipyridyl ruthenium(II) complex "cis-Ru(4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine)(Ln)(NCS)2 H101", where Ln = 4,4'-dicarboxylic acid-2,2'-bipyridine; was synthesized and characterized by 1H-NMR, FT-IR and ESI-MASS spectroscopes. The H101 sensitized solar cell constructed with an active area of 0.54 cm2 in combination with an ionic liquid electrolyte exhibited broader photocurrent action spectrum with solar-to-electric energy conversion efficiency (𝜂) of 5.89 (JSC = 12.14 mA/cm2, VOC = 690 V, fill factor = 0.699) under Air Mass (AM) 1.5 sunlight, while the reference `cis-Ru(4,4'-dinonyl-2,2'-bipyridine)(Ln)(NCS)2', Z907 sensitized solar cell exhibited 𝜂-value of 5.17% (JSC = 11.93 mA/cm2, VOC = 650 V, fill factor = 0.666). TGA analysis of H101 showed extended thermal-stability and under continuous light exposure and aging at 55°C, the DSSC retained 85% of its initial 𝜂-value, while under comparable conditions Z907 sensitized solar cell retained 88%. As compared to 4,4'-dinonyl-2,2'-bipyridine in Z907, the new ancillary bipyridyl ligand `4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine’ in H101 shifts the absorption bands remarkably towards blue. The Density Functional Theory (DFT) and Time-Dependent DFT excited state calculations of the new sensitizer show that the first three HOMOs have t2g character with sizeable mixing from the NCS ligands with 𝜋-bonding orbitals of 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine. The LUMO is a $\pi^\ast$-orbital localized on the 4,4-dicarboxylic acid-2,2'-bipyridine and higher un-occupied frontier orbitals have $\pi^\ast$-combinations with 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine.

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