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Anatase TiO2 Nanoparticles With Exposed {001} Facets for Efficient Dye-Sensitized Solar Cells

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Anatase TiO2 Nanoparticles With Exposed {001} Facets for Efficient Dye-Sensitized Solar Cells

Liang Chu et al. Sci Rep.

Abstract

Anatase TiO2 nanoparticles with exposed {001} facets were synthesized from Ti powder via a sequential hydrothermal reaction process. At the first-step hydrothermal reaction, H-titanate nanowires were obtained in NaOH solution with Ti powder, and at second-step hydrothermal reaction, anatase TiO2 nanoparticles with exposed {001} facets were formed in NH4F solution. If the second-step hydrothermal reaction was carried out in pure water, the H-titanate nanowires were decomposed into random shape anatase-TiO2 nanostructures, as well as few impurity of H2Ti8O17 phase and rutile TiO2 phase. Then, the as-prepared TiO2 nanostructures synthesized in NH4F solution and pure water were applied to the photoanodes of dye-sensitized solar cells (DSSCs), which exhibited power conversion efficiency (PCE) of 7.06% (VOC of 0.756 V, JSC of 14.80 mA/cm(2), FF of 0.631) and 3.47% (VOC of 0.764 V, JSC of 6.86 mA/cm(2), FF of 0.662), respectively. The outstanding performance of DSSCs based on anatase TiO2 nanoparticles with exposed {001} facets was attributed to the high activity and large special surface area for excellent capacity of dye adsorption.

Figures

Figure 1
Figure 1. XRD powder patterns and Raman spectroscopy.
(a) H-titanate nanowires corresponded well to H2Ti5O11·H2O phase (I), the obtained sample after the second-step hydrothermal reaction in pure water was indexed as mainly anatase TiO2 phase and few H2Ti8O17 phase and rutile TiO2 phase (II), the obtained sample in NH4F solution was indexed as pure anatase TiO2 phase (III). (b) Raman spectroscopy was taken to calculate the percentage of {001} facets as 34% by the peak intensity ratio of the Eg (at 144 cm−1) and A1g (at 514 cm−1) peaks.
Figure 2
Figure 2. SEM images of the as-prepared TiO2.
(a,b) Without NH4F, the obtained TiO2 nanostructures were random shapes. (c,d) With NH4F, regular TiO2 nanoparticles were obtained.
Figure 3
Figure 3. TEM and HRTEM images of the as-prepared samples.
(a,b) H-titanate nanowires, (c, d) random shape TiO2 nanostructures obtained in pure water, (e,f) truncated octahedron TiO2 nanoparticles obtained in NH4F solution.
Figure 4
Figure 4. Schematic illustration of the synthetic route of TiO2.
In pure water, random shape anatase TiO2 with few H2Ti8O17 and rutile TiO2 nanostrutures were formed. While in the present of NH4F, truncated octahedron TiO2 nanoparticles with exposed {001} facets were obtained.
Figure 5
Figure 5. Photovoltaic characteristics of the DSSCs based on random shape TiO2 nanostructures (noted “Without F”) and truncated octahedron TiO2 nanoparticles with exposed {001} facets (noted “With F”).
(a) I-V curves. (b) Nyquist plots by EIS measurements. (c) Open-voltage decay measurement upon turning off the illumination. (d) Electron lifetime determined from the data of (c).
Figure 6
Figure 6. N2 adsorption isotherms and absorption spectra.
(a) N2 adsorption isotherms of random shape TiO2 nanostructures (noted “Without F”) and truncated octahedron TiO2 nanoparticles (noted “With F”). (b) UV-Vis absorption spectrum of random shape TiO2 nanostructure films (without/with sensitizing, i/iii) and truncated octahedron TiO2 nanoparticle films (without/with sensitizing, ii/iv) on FTO substrates. The inset shows optical images of TiO2 films (without/with sensitizing) on FTO substrates.

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