Further Understanding of the Adsorption Mechanism of N719 Sensitizer on Anatase TiO₂ Films for DSSC Applications Using Vibrational Spectroscopy and Confocal Raman Imaging

Abstract

Vibrational spectroscopic studies of N719 dye-adsorbed TiO(2) films have been carried out by using SERRS, ATR-FTIR, and confocal Raman imaging. The high wavenumber region (3000-4000 cm(-1)) of dye adsorbed TiO(2) is analyzed via Raman and IR spectroscopy to investigate the role of surface hydroxyl groups in the anchoring mode. As a complementary technique, confocal Raman imaging is employed to study the distribution features of key dye groups (COO-, bipyridine, and C=O) on the anatase surface. Sensitized TiO(2) films made from two different nanocrystalline anatase powders are investigated: a commercial one (Dyesol) and our synthetic variety produced through aqueous synthesis. It is proposed the binding of the N719 dye to TiO(2) to occur through two neighboring carboxylic acid/carboxylate groups via a combination of bidentate-bridging and H-bonding involving a donating group from the N719 (and/or Ti-OH) units and acceptor from the Ti-OH (and/or N719) groups. The Raman imaging distribution of COO(-)(sym) on TiO(2) was used to show the covalent bonding, while the distribution of C=O mode was applied to observe the electrostatically bonded groups.

Vibrational Spectroscopy of Complex Synthetic and Industrial Products

“…To verify such types of results the use of stearic acid was also investigated in parallel . Most previous works over the last decades on this system have largely focused only on the dye IR and Raman vibrational structure (1000-2600 cm -1 ); in our investigations Lee et al, 2010Lee et al, , 2011aLee et al, , 2011b, the use of the higher wavenumber region in the pure photosensitzer dye, pure nano-crystalline anatase substrates and after sensitization was investigated. As will be shown below, the analysis of the higher wavenumber region contributed greatly to the results gathered in this study.…”

“…ATR-IR spectra (Hydroxyl region) and corresponding images of the pure TiO 2 substrates (Dyesol and Aqueous) and that of the adsorbed N719-TiO 2 system. (Lee et al , 2011b One of the main aspects of our work Lee et al, 2010Lee et al, , 2011aLee et al, , 2011b was to compare how two similar nano-crystalline anatase TiO 2 substrates (a commercial_Dyesol and our own synthetic Aqueous product) behaved in terms of their bonding properties (via vibrational spectroscopy), distributions (via vibrational imaging) and later from an electronic interaction perspective (Lee et al, 2011b) not only from the photosensitzer (N719_Dye) perspective but also from the substrate point of view. From Figure 12 above, it became apparent to us that the synthetic product produced under different conditions then the commercial TiO 2 substrate (Dyesol) contained a large number of surface OH/H 2 O groups in comparison to the commercial product.…”

“…New Binding mechanism for the N719-TiO system based on our vibrational spectroscopic and imaging data. Therefore, based on the vibrational spectroscopic and imaging data gathered we proposed a new modified structure for the binding mechanism of N719 dye on TiO 2 which has now become the standard accepted model by all the leading experts/pioneers in the field (see citations of Lee et al, 2010). Although Bazzan et al 2011 recently published an article that stated that "there is as yet no commonly accepted understanding of the biding mechanism", in their published work, they used our proposed concepts and binding mechanism to explain the binding mechanism in their work.…”

Effect of neodymium on the photoconversion efficiency of TiO2 based dye sensitized solar cells

“…Among these, Titanium dioxide and/or titanate nanotubes have gained promising and important place after the innovative work of Kasuga et al [12]. Much work has been done and reported on the phase dependent properties of TiO 2 with emphasis on anatase phase resulting in stable material with less electron recombination probability [13][14][15][16][17][18][19]. The recent trend is use of composite metal oxides as a suitable material for photoconversion.…”

Nanostructured Dye Sensitized Solar Cells

“…After a decade long debate on the interaction of the N719/TiOx system, [16][17][18][19][20] these anchoring mechanisms has been finally described by Lee and coworkers in 2010, who found that the N719 molecules interact via both electrostatic (Hbonding) and covalent (bidentate-bridging) interactions [31]. In detail, one of the two carboxylic groups (COO-or COOH) of N719 seems to bind to TiOx using bidentate bridging for chemisorption (i.e.…”