Ravi Kumar Kanaparthi

Molecular engineering of sensitizers for dye‐sensitized solar cell applications

Dye-sensitized solar cells (DSSCs) have attracted considerable attention in recent years as they offer the possibility of low-cost conversion of photovoltaic energy. This account focuses on recent advances in molecular design and technological aspects of sensitizers based on metal complexes, metal-free organics and tetrapyrrolic compounds which include porphyrins, phthalocyanines as well as corroles. Special attention has been paid to the design principles of these dyes, and co-sensitization, an emerging technique to extend the absorption range, is also discussed as a way to improve the performance of the device. This account also focuses on recent advances of efficient ruthenium sensitizers as well as other metal complexes and their applications in DSSCs. Recent developments in the area of metal-free organic and tetrapyrrolic sensitizers are also discussed.

Phosphorus(V)corrole- Porphyrin Based Hetero Trimers: Synthesis, Spectroscopy and Photochemistry

Abstract‘Axial-bonding’-type hetero trimers have been constructed by employing a simple ‘inorganic’ reaction such as axial bond formation of main group element containing phosphorus corrole. The approach is simple and modular in nature. The architecture of these hetero trimers such that, while a phosphorus(V)corrole forms the basal scaffolding unit, either two free-base porphyrins [(H2)2–PCor] or ZnII porphyrins [(Zn)2–PCor] occupy the two axial sites via an aryloxy bridge. Both hetero trimeric species have been completely characterized by mass (FAB), UV/Vis, proton nuclear magnetic resonance spectroscopies and also by the differential pulse voltammetric method. Comparison of their spectroscopic and electrochemical data of these trimers with those of the corresponding reference compounds reveal that there is no apparent ring-to-ring interactions in these ‘vertically’ linked hetero trimers. Reduced fluorescence quantum yields were observed for [(H2)2–PCor] and [(Zn)2–PCor] when compared to corresponding monomeric chromophores. Finally, a comparison is made between the presently reported phosphorus(V)corrole based hetero arrays and the previously reported analogous arrays based on Ge(IV)corrole with regard to their spectroscopic properties and photochemical activities.

β-pyrrole substituted porphyrin–pyrene dyads using vinylene spacer: Synthesis, characterization and photophysical properties

AbstractWe have designed and synthesized donor–acceptor conjugates having donor pyrene at the pyrrole-β position of either free-base porphyrin or Zn(II) porphyrin using vinylene spacer. Both the dyads have been completely characterized by elemental analysis, MALDI-MS, UV-Vis., and fluorescence (steady state and time-resolved) spectroscopies as well as cyclic voltammetry. The absorption maxima of both dyads are red-shifted by 8–12 nm. The ground state properties showed that there exist minimum π–π interaction between the aromatic subunits of these D–A systems. Quenched emission was observed in both the dyads when excited at 290 nm. The quenched emission explained in terms of intramolecular excitation energy transfer competes with the photo-induced electron transfer reaction in these D–A system. Graphical AbstractDonor–acceptor systems in which a donor pyrene unit is connected at pyrrole-β position using a vinylene spacer of either free-base or Zn(II) porphyrin have been synthesized and characterized. The ground state properties showed that there exists minimum π–π interactions between pyrene and porphyrin macrocycle. Quenched emission was observed in both the dyads when excited at 290 nm. The quenched emission explained in terms of intramolecular excitation energy transfer competes with the photo-induced electron transfer reaction in these D–A system.

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

AbstractTwo 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. Graphical AbstractTwo push-pull carbazole based molecules, CAR-THIOHX and CAR-TPA, have been designed and synthesized by simple organic transformations. Photophysical and electrochemical studies revealed the potential of these two molecules 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.