Improvement of photovoltages in organic dye-sensitized solar cells by Li intercalation in particulate TiO2 electrodes

Harima, Yutaka; Kawabuchi, K.; Kajihara, Shiho; Ishii, Ayako; Ooyama, Yousuke; Takeda, Kazuhiko

doi:10.1063/1.2711659

Cited by 28 publications

(23 citation statements)

References 15 publications

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“…4,5 They thus become ideal candidates as dye photosensitizers. [6][7][8][9][10][11] In addition, these dye molecules have other applications in laser dyes, 4, 5 solvation and fluorescence probe molecules. [12][13][14][15][16][17][18][19][20][21][22] Coumarin 343 (C343, see Fig.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

Cao

Zhao

2012

The Journal of Chemical Physics

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The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications.

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Section: Introductionmentioning

confidence: 99%

“…1) is one of 7-amino coumarins and has been already used in DSSC. 7,[9][10][11] It has a rigid julolidine structure and was first reported in 1975 with a high quantum yield of fluorescence in ethanol. 4 Its crystal was first prepared from a chloroform solution by slow evaporation in 1996.…”

Section: Introductionmentioning

confidence: 99%

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

Cao

Zhao

2012

The Journal of Chemical Physics

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“…Adding lithium to the electrolyte allows control of the electron injection yield from the dye to the TiO 2 electrodes [20][21][22][23] and the rate of interfacial charge recombination, 24 as well as increasing both the conductivity of the electrodes, 25 and resultant photovoltages. 26 Although surface polarization is likely to play a large role, 25 given the ease with which Li intercalates into anatase TiO 2 some interstitial Li is expected to be present. It has been suggested that interstitial lithium modifies the distribution of charge traps within the TiO 2 substrate, [26][27][28] with a consequential effect on the dynamics of charge carriers diffusing through the electrode.…”

Section: Introductionmentioning

confidence: 99%

“…26 Although surface polarization is likely to play a large role, 25 given the ease with which Li intercalates into anatase TiO 2 some interstitial Li is expected to be present. It has been suggested that interstitial lithium modifies the distribution of charge traps within the TiO 2 substrate, [26][27][28] with a consequential effect on the dynamics of charge carriers diffusing through the electrode. This interaction between intercalated lithium and electrons resident within the Ti sublattice has theoretical support from interatomic forcefield calculations of Olson et al 27 who predicted strong binding between interstitial Li and a neighboring Ti in a +3 oxidation state.…”

Section: Introductionmentioning

confidence: 99%

GGA+Udescription of lithium intercalation into anataseTiO2

2010

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We have used density-functional theory ͓generalized gradient approximation ͑GGA͔͒ to study lithium intercalation at low concentration into anatase TiO 2 . To describe the defect states produced by Li doping a Hubbard "+U" correction is applied to the Ti d states ͑GGA+ U͒. Uncorrected GGA calculations predict Li x TiO 2 to be metallic with the excess charge distributed over all Ti sites, whereas GGA+ U predicts a defect state 0.96 eV below the conduction band, in agreement with experimental photoelectron spectra. This occupied defect state corresponds to charge strongly localized at a single Ti 3d site neighboring the intercalated lithium with a magnetization of 1 B. This polaronic state produces a redshifted optical absorption spectrum, which is compared to those for the native O-vacancy and Ti-interstitial defects. The strong localization of charge at a single Ti center lowers the symmetry of the interstitial geometry relative to that predicted by GGA. The intercalated lithium sits close to the center of the octahedral site, occupying a single potential energy minimum with respect to displacement along the ͓001͔ direction. This challenges the previous interpretation of neutron diffraction data that there exist two potential energy minima separated by 1.6 Å along the ͓001͔ direction within each octahedron. Nudged elastic band calculations give barriers to interoctahedral diffusion of ϳ0.6 eV, in good agreement with experimental data. These barrier heights are found to depend only weakly on the position of the donated electron. The intercalation energy is 2.14 eV with GGA and 1.88 eV with GGA+ U, compared to the experimental value of ϳ1.9 eV. Li-electron binding energies have also been calculated. The ͓Li i• -Ti Ti Ј ͔ complex has a binding energy of 56 meV, and a second electron is predicted to be bound to give ͓Li i• -2Ti Ti Ј ͔ with a stabilization energy of 30 meV, indicating that intercalated lithium will weakly trap excess electrons produced during photoillumination or introduced by additional n-type doping.

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“…Photovoltages of nanoporous TiO 2 based DSSCs were improved by up 200 mV with negligible decrease in photocurrent by treating TiO 2 electrodes with an intercalation of Li + . 53 The enhancement of photovoltage is explained in terms of the formation of a dipole layer due to adsorption of Li + on the TiO 2 surface generated by the reaction of intercalated Li atoms with moisture in the air. Addition of lithium salt Li[(CF 3 SO 2 ) 2 N] to the spin coating solution of the hole conductor also resulted in a strong performance increase in the final device.…”

Section: Electrochemical Photovoltaic Cells Without Dyesmentioning

confidence: 99%

Electrochemical photovoltaic cells—review of recent developments

Wei

Andrew

Ryhänen

2010

J of Chemical Tech & Biotech

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Photoelectrochemistry is attracting extensive attention from scientists worldwide for its use in converting light energy into electricity in electrochemical photovoltaic cells, the most common form of which, dye sensitized solar cells (DSSCs), can offer both flexibility and transparency. Their efficiencies are now comparable with amorphous silicon solar cells but at a much lower cost. This review covers not only the fundamentals of electrochemical photovoltaic cell operation but also recent advances in research and development for industrial applications. The most recent research topics relating to DSSCs, for example, applications of nanostructured n-type semiconducting electrodes, ionic liquid electrolytes and graphene and carbon nanotube electrodes are all included. In addition, the storage of electrochemical energy by electrochemical photovoltaic cells has also been reviewed.

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Improvement of photovoltages in organic dye-sensitized solar cells by Li intercalation in particulate TiO2 electrodes

Cited by 28 publications

References 15 publications

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

GGA+Udescription of lithium intercalation into anataseTiO2

Electrochemical photovoltaic cells—review of recent developments

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