Computational, spectrophotometric and photoelectrochemical studies of eco-friendly synthetic ions of novel 3’,4’-dihydroxy-7-(N,N-diphenylamino)flavylium (JAD90) and its analogues as sensitizers in dye-sensitized solar cells.

Ilaria Citro^a, Giuseppe Calogero^a, Gaetano Di Marco^a, Stefano Caramori^b, Carlo Alberto Bignozzi^b, João Avò^c, A. Jorge Parola^c, Fernando Pina^c

^aCNR-IPCF, viale F. Stagno D'Alcontres 37, MESSINA I- 98158, Italy

^bUniversity of Ferrara, Italy, Via Fossato di Mortara, 17, Ferrara, Italy

^cREQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal

International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)

Ecublens, Switzerland, 2014 May 11th - 14th

Organizers: Michael Graetzel and Mohammad Nazeeruddin

Poster, Ilaria Citro, 305
Publication date: 1st March 2014

We present a complete study on four synthetic flavylium salts employed as sensitizers for dye-sensitized solar cells (DSSCs). The effect of several donor groups in the flavylium molecular structure was investigated (1). The theoretical evaluation of the electron density in the HOMO and LUMO of the dye molecules and the vertical electronic excitations were calculated using the time-dependent density functional theory (TDDFT) with B3LYP functional and the same basis set above-mentioned (2). The oxidation potentials and the excitation energies for the investigated dyes were determined from TDDFT analysis. The molecules ground state geometries and the frontier orbital plots of HOMO and LUMO were drawn and calculated by Gaussian 09 software. The computation indicated that these molecules can interact strongly with the TiO₂ surface by a single OH group of the catechol, and can inject efficiently into the TiO₂. The Electron Density Difference Maps (EDDM) maps of the four dyes confirm the substantial π-π* character of the lowest singlet excited states, with the first, and most intense lowest energy transition exhibiting a stronger charge transfer (CT) character, involving a substantial shift from the dihydroxybenzene unit to the benzopyrylium ring.The interaction of selected dye models (B and G) with an anatase surface slab (101) consisting of 108 atoms (Ti₃₆O₇₂) was explored by ONIOM multilayer methods, where the molecule and the Ti-O atoms to which was attached was treated by ab-initio methods (DFT-B3LYP-LAN2DZ), while the remaining part of the TiO₂ cluster was optimized at the Molecular Mechanics (MM) level employing the Universal Force Field (UFF) with charge embedding.The dyes B-D-G and F were found to be luminescent in fluid solution where, in the case of D and G a structured emission was observed.The electrochemical behaviour of these flavylium dyes is generally characterized by irreversible processes. Calculations indicated that JAD90 (F) displays an higher exciton binding energy which may be responsible for a lower charge injection quantum yield. Moreover, aggregation involving πinteractions or a less favorable interplay with I^- could cause incomplete dye regeneration, observed with laser flash-photolysis.

We gratefully acknowledge PON– Industria 2007-2013: Progetto FotoRiduCO2 (prot. PON01_02257), ENERGETIC (prot. PON02_00355_3391233) and TESEO (prot. PON02_00153_2939517). Furthermore this research was finacial supported by “CNR-EFOR” Project and by Project “SAGRO” supported by Regione Siciliana (PO-FESR 2007/2013 linea d’intervento 4.1.1.1) and by Fundação para a Ciência e Tecnologia through the National Portuguese NMR Network, grant PEst-C/EQB/LA0006/2011 and project PTDC/QUI-QUI/119932/2010.

Fig. 1 Scheme of molecular structures of the four investigated flavylium
(1) F. Pina et al. Chem Soc Rev 2011, DOI: 10.1039/c1cs15126f (2) G. Calogero et al. Photochem. Photobiol. Sci. 12 (2013) 883

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