• LINGAMALLU GIRIBABU

      Articles written in Journal of Chemical Sciences

    • Carbazole-based sensitizers for potential application to dye sensitized solar cells

      Naresh Duvva Ravi Kumar Kanaparthi Jaipal Kandhadi Gabriele Marotta Paolo Salvatori Filippo De Angelis Lingamallu Giribabu

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      Two push-pull molecules employing carbazole and alkyl thiophene (CAR-THIOHX) or carbazole and triphenylamine (CAR-TPA) as donor moieties, with the cyanoacrylic group as the acceptor, have been designed and synthesized by simple organic transformations. Photophysical and electrochemical studies revealed the potential of these two systems in dye sensitized solar cells (DSSC). Under standard irradiation conditions, CAR-TPA and CAR-THIOHX exhibited 2.12 and 1.83% of overall power conversion efficiencies respectively. The moderate photovoltaic efficiency of the sensitizers has been attributed to the poor light absorption of the sensitizers in the visible region. Density functional theory (DFT) calculations have shown a strong intramolecular charge transfer character, with the HOMOs of both the sensitizers exclusively localized on the corresponding donor moieties and LUMOs on the cyanoacrylic acid acceptor. On the other hand, the calculated high dihedral angle between the carbazole donor and the phenyl bridge for these sensitizers impedes the conjugation along the dyes backbone, and thus leads to less extended and intense absorption spectra in the visible region.

    • Triphenylamine corrole dyads: Synthesis, characterization and substitution effect on photophysical properties

      KOLANU SUDHAKAR LINGAMALLU GIRIBABU

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      We present our results on the effect of substitution on the photophysical properties of donoracceptor (D-A) systems in which triphenylamine is the donor and substituted corroles i.e., 5,15-phenyl-10- triphenylaminecorrole TPACor 1, 5,15-di(3,5-ditertbutylphenyl)-10-triphenylaminecorrole TPACor 2, and5,15-(4-nitrophenyl)-10-triphenylaminecorrole TPACor 3 is the acceptor. All three dyads have been characterized by elemental analysis, MALDI-MS, cyclic voltammetry, UV-Vis and fluorescence (steady state and timeresolved)spectroscopies. Both Soret and Q bands of TPACor 3 are red-shifted when compared to other two dyads due to the presence of electron withdrawing nitro group. Similarly, redox properties of TPACor 3 are altered, when correlated to TPACor 1 and TPACor 2 dyads. However, the fluorescence emission of triphenylamine in all three dyads was quenched significantly (>90%) compared to its monomeric unit. The presence of either electron releasing or electron withdrawing group on corrole moiety has not much effect on the photophysicalproperties. The quenched emission was attributed to intramolecular excitation energy transfer and the photoinduced electron transfer reactions contested in these dyads.

    • Triphenylimidazole Based Dye-Sensitized Solar Cells for Efficient Solar and Artificial Light Conversion using Iodide/Triiodide Redox Electrolyte

      PALIVELA SIVA GANGADHAR ANOOJA JAGADEESH ANDREW SIMON GEORGE SURAJ SOMAN LINGAMALLU GIRIBABU

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      Though metal complex-based redox couples showed promising results in test cell devices of dye sensitized solar cells (DSSCs), it hampers the scale-up of modules/panels due to mass transport and recombination issues. Copper (II/I) redox couple-based DSSCs have dispensed exceptional results at diffused/artificial indoor light conditions as potential candidates for Internet of Things (IoT) applications. Recently,our group have reported triphenylimidazole based metal-free organic dyes (LG-P series) with [Cu(tmby)2]2+/+ (tmby = 4,4',6,6'-tetramethyl-2,2'-bipyridine) redox couple realizing device efficiency of ~10% under low-light conditions. In the present study, we extended the work using iodide-triiodide (I-/I3-)redox couple with LG-P series of sensitizers and measured the device efficiencies under both full sun(100 mW/cm2) and low-light conditions (1000 lux indoor illumination). Under full sun condition, LG-P3 hasdelivered a power conversion efficiency (PCE) of 2.15%, whereas at 1000 lux daylight, LED LG-P1 showed aPCE of 10.53%, and at 1000 lux daylight CFL LG-P3 showed PCE of 9.19%, which we observed with I-/I3 redox electrolyte. We have adopted charge extraction (CE), open-circuit voltage decay (OCVD) and electrochemicalimpedance spectroscopy (EIS) to explain the efficiency differences in LG-P series of dyes.

      Mass transport and recombination are two hurdles for metal complex-based redox couples for dye-sensitized solar cells. We have fabricated DSSC devices using triphenylimidazole-based organic dyes with I/I3 redox electrolyte and measured its device efficiency under full sun and artificial/indoor light conditions and the potential for the Internet of Things (IoT) applications.

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