Theoretical Studies of Photoinduced Electron Transfer in Dye-Sensitized TiO 2

Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
Annual Review of Physical Chemistry (Impact Factor: 16.84). 02/2007; 58(1):143-84. DOI: 10.1146/annurev.physchem.58.052306.144054
Source: PubMed


This review describes recent research into the properties of the chromophore-TiO2 interface that forms the basis for photoinduced charge separation in dye-sensitized semiconductor solar cells. It focuses particularly on an atomistic picture of the electron-injection dynamics. The interface offers an excellent case study, pertinent as well to a variety of other photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. The differences between chemists' and physicists' models for describing molecules and bulk materials, respectively, create challenges for the characterization of interfaces that include both of these components. We give an overall picture of the interface by starting with a description of the properties of the chromophores and semiconductor separately, and then by discussing the coupled system, including the chromophore-semiconductor binding, electronic structure, and electron-injection dynamics. Explicit time-dependent modeling is particularly valuable for an understanding of the ultrafast electron injection because it shows a variety of individual injection events with well-defined dynamical features that cannot be made apparent by an average reaction-rate description.

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Available from: Oleg Prezhdo, Jan 01, 2015
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    • "In the indirect injection mechanism , dyes are excited from the ground states and then the excited electron is injected into the CB of the semiconductor [46] [50] [51]. Furthermore, Duncan and coworkers [46] reported the electronic behavior of some dye molecules were in between of the two injection mechanisms, which are related to the relative energy level of the molecule LUMO to the bottom of the semiconductor conduction band and the electronic coupling between semiconductor and dye molecule [48]. For different F atom substitution, there were great differences about energy levels. "
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    ABSTRACT: Based on titanium dioxide model and LJBs sensitizers (triphenylamine as the donor, 3,4-ethylene dioxy thiophene plus various functionalized phenylenes as the π-spacer, and cyanoacrylic acid as the anchoring group) with different connection types on TiO2 substrate, the reasonable dye-TiO2 connection has been located. The results show that the dissociative adsorption of LJBs is more thermodynamically favorable than the neutral molecule bound configurations. LJBs adsorb onto TiO2 via interaction between 3d orbital of surface Ti atom and 2p orbital of N/O atoms in the acceptors. This result is confirmed in both neutral and dissociation forms of LJBs molecules. According to our calculations, adding a meta-fluorine substituent to the phenyl group of cyanoacrylic acid (LJB-Fm) may damage the planarity and conjugation. Consequently, the light harvesting efficiency decreased, and that is particularly unfavorable for the DSSCs application. The Ortho F-substituted dye (LJB-Fo), however, exhibited enhanced light absorption and more efficient intra-molecular charge transport. The bigger Jsc, Voc values of LJB-Fo system predicts its superior DSSC performance. Additionally, LJBs anchored on TiO2 surface via group –COO (LJB-H and LJB-Fo) lead to an indirect mechanism for electron injection. While LJB-Fm preferred to direct electron injection mechanism due to the strong orbital-coupling between sensitizer and the TiO2 substrate.
    Full-text · Article · Sep 2015 · Computational and Theoretical Chemistry
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    • "Dye sensitized solar cells (DSSCs) [1] [2] [3], one of the most promising environmentally friendly molecular photovoltaics, have gained immense interest over the past several decades because of their low cost, easy fabrication, flexibility and relatively high efficiency [4] [5] [6] [7]. Up to now, a record power conversion efficiency (PCE) of 13.0% has been reported recently based on the panchromatic porphyrin sensitizer and cobalt (II/III) redox shuttle [7]. "
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    ABSTRACT: The structural and electronic properties of four phenothiazine-based sensitizers (TMH-CNcis, TMH-CNtrans, TMH-COOH, and TMH-2COOH) have been examined by means of density functional theory (OFT) and time-dependent DFT calculations. And the periodic DET method is used to investigate the adsorption of dyes on the TiO2 anatase (1 0 1) surface within the DMo1(3) code. The results promise that anchor dyes with strong withdrawing CN group can effectively injected electrons to the conduction band of semiconductor TiO2 surface implying that TMH-CNcis and TMH- CNtrans will show better performance among four dyes. Particularly, the adsorption energies and charge density difference maps are calculated to investigate the possible adsorption modes of the dye on the TiO2 surface. After establishing the preferred anchoring configurations, we performed a detailed analysis on the electronic structures of the dye-TiO2 complexes to explore the absorption spectra, charge distribution and the composition of the density of states (DOS), providing a quantitative description of the variation in electronic coupling induced by the different anchoring group. The results show that after binding to the semiconductor, the absorption spectra of four dyes-TiO2 complexes are all red-shifted significantly as compared to that of the isolated dyes, and the TMH-CNtrans-TiO2 will transfer more electrons during the photoexcitation, showing an obvious charge transfer characteristic.
    Full-text · Article · Oct 2014 · Computational and Theoretical Chemistry
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    • "The bottlenecks lie in either the low electron injection efficiency or the limited broadening of absorption spectra. Hydroxy is another promising anchoring group because it can form a strong chromophores-semiconductor coupling with least spatial arrangements [32]. Hemicyanine dyes with a hydroxy group were investigated by Yao et al. [33] and Chen et al. [34] they have found that electron injection rate increases which gave better efficiency as compared to carboxy group alone. "
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    ABSTRACT: Two novel organic dyes containing hydroxy and octyloxy substituents onto a phenothiazine skeleton were synthesized and their effects on the photovoltaic performance were studied. Hydroxy acts as an ancillary anchoring unit along with the carboxylic group, while the phenothiazine modified moiety acts as an electron donor. The photophysical and electrochemical studies revealed that maximum absorbance of the dye with the hydroxy group in the solution was blue shifted and its band gap increased, indicating that donor acceptor strength was reduced as compared to the octyloxy substituted dye. Furthermore, electron lifetime of the organic dye with the hydroxy moiety was shorter due to smaller resistance of electron recombination. Contrarily the dye with octyloxy moiety exhibited higher electron lifetime and open-circuit photovoltage leading to an overall power conversion efficiency of 6.32% under standard AM 1.5G illumination. The IPCE was over 80% in the region between 450 and 500 nm.
    Full-text · Article · Nov 2013 · Dyes and Pigments
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