Structural parameters controlling the performance of organized mesoporous TiO2 films in dye sensitized solar cells

Titanium dioxide films with organized mesoporous structure were investigated as photoanodes in dye sensitized solar cells. High-quality films were grown on FTO supports by implementing the protocol of supramolecular templating with an amphiphilic triblock copolymer, Pluronic P123. Thicker films were obtained by repeated dip-coating and calcination cycles of up to 10 layers. The TiO2 films were crack-free, optically transparent, and had thicknesses exceeding 2 mu m, while still preserving the organized mesoporous morphology. Their roughness factors, determined from Kr-adsorption isotherms, exceeded 500. The sorption of N-3 and N-719 dyes was fitted to a surface coverage of 0.31 molecules/nm(2), which is about one third of the ideal dye loading assumed for the ( 101) anatase face. The solar performance of multilayer films sensitized with N-945 dye scaled linearly for 1-3 layer films, but approached a plateau for thicker films. (c) 2007 Elsevier B.V. All rights reserved

Organized Mesoporous TiO2 Films Stabilized by Phosphorus: Application for Dye-Sensitized Solar Cells

A synthetic protocol was developed for the preparation of thin mesoporous TiO2 films with enhanced thermal stability. This objective was achieved by a modification of the procedure of supramolecular templating by a Pluronic P-123 copolymer by an addition of a small amount of phosphoric acid to the precursor solution. Thin mesoporous TiO2 films up to 2.3 mu m thick were prepared via layer-by-layer deposition. The roughness factor exceeding 1300 was achieved on these films. After annealing at 540 degrees C, well-developed 5-6 nm anatase nanocrystals were present in the pore walls of a still perfect mesoporous structure. The pore coalescence and structure collapse during heat-treatment were effectively hindered by the presence of phosphorus. Our P-modified mesoporous TiO2 films were sensitized with the N-945 dye and used as photoanodes of the dye-sensitized solar cells. They reached the conversion efficiency of 5.03 or 5.05% for the film thickness of 1.8 or 2.3 mu m, respectively. Whereas the roughness factor scaled linearly with the number of layers, the solar conversion efficiency reached a constant value for films consisting of eight or more layers. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3250958] All rights reserved

Multi-walled carbon nanotubes functionalized by carboxylic groups: Activation of TiO2 (anatase) and phosphate olivines (LiMnPO4; LiFePO4) for electrochemical Li-storage

Multi-walled carbon nanotubes functionalized by carboxylic groups, exhibit better affinity towards TiO2 (P90, Degussa) as compared to that of pristine nanotubes. Also the electrochemical performance of TiO2 is improved by nanotube networking, but the Li-storage capacity of TiO2 is unchanged. Whereas the composite of TiO2 with non-functionalized nanotubes demonstrates simple superposition of the behavior of pure components, the composite with functionalized nanotubes shows unique faradaic pseudocapacitance which is specific for this composite only. The surface functionalization of nanotubes enhances charge storage capacity and reversibility of a composite with LiMnPO4 (olivine), but mediates also the electrolyte breakdown at potentials >4.2 V. Whereas the electrochemical activation of LiMnPO4 (olivine) by functionalized nanotubes is quite modest, excellent performance was found for LiFePO4 (olivine) in composite materials containing only 2 wt% of functionalized nanotubes. (C) 2010 Elsevier B.V. All rights reserved

Electron Kinetics in Dye Sensitized Solar Cells Employing Anatase with (101) and (001) Facets

Two phase-pure nanocrystalline anatase materials differing in the exposed crystal facets (001) or (101) are studied by electrochemical impedance spectroscopy and by transient photovoltage and photocurrent decay in dye sensitized solar cells. A larger chemical capacitance, indicating larger density of states, is observed for anatase (001). The presence of deep electron traps in (001) nanosheets is further confirmed by optical (UV-Vis) and photoemission (XPS, UPS) spectra. The difference in chemical capacitance indicates a slower diffusion of electrons in the (001) anatase material, but also a higher electron lifetime compared to (101) anatase material. (C) 2015 Elsevier Ltd. All rights reserved

Voltage enhancement in dye-sensitized solar cell using (001)-oriented anatase TiO2 nanosheets

A nanocrystalline TiO2 (anatase) nanosheet exposing mainly the (001) crystal faces was tested as photoanode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO2 support from the TiO2 suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage characteristics of dye-sensitized solar cell