Multifunctional Photocatalytic Materials for Energy by Zhiqun Lin Meidan Ye Mengye Wang & Meidan Ye & Mengye Wang

Author:Zhiqun Lin,Meidan Ye,Mengye Wang & Meidan Ye & Mengye Wang
Language: eng
Format: epub
ISBN: 9780081019788
Publisher: Elsevier Ltd.
Published: 2018-03-19T16:00:00+00:00

Fig. 8.3 shows the TEM images of typical TiO2 NPs obtained by the sol-gel method [16].

Fig. 8.3 TEM images of synthesized (A) spherical, (B) rod-like, and (C) wire-like TiO2 nanocrystals; (D) HR-TEM image of wire-like TiO2. Reprinted with permission from S. Lee et al., Two-step sol–gel method-based TiO2 nanoparticles with uniform morphology and size for efficient photo-energy conversion devices. Chem. Mater. 22 (2010) 1958–1965.

8.2.1.2 Fabrication of TiO2 NRs/NWs

Because of their high electron diffusivity, large specific surface area, and their ability to restrain the redox reactions among carriers, TiO2 NRs/NWs have been widely used as one-dimensional (1D) photoanode materials in thin-film solar cells. Various techniques have been employed to fabricate 1D nanomaterials for thin-film solar cells, including chemical vapor deposition (CVD), electrodeposition, pulsed laser deposition (PLD), etching, and the hydrothermal method. Among these techniques, the hydrothermal method is the one most widely used to fabricate high-quality TiO2 NRs/NWs because of its low cost, its easy operation, the simplicity of the process and the equipment used in the process, and its suitability for mass production of nanomaterials. To obtain high-ordered TiO2 NWs/NRs on transparent conducting substrates (TCSs), a thin compact TiO2 layer is usually utilized as a seed layer to grow monocrystalline arrays. Grimes et al. first grew crystalline TiO2 NW arrays directly onto transparent conducting oxide (TCO) substrates via a nonpolar solvent/hydrophilic substrate interfacial reaction under mild hydrothermal conditions [17]. In this process, a compact TiO2 layer ~ 20 nm thick was coated on the F-doped SnO2 (FTO) glass by immersing it in a 0.2 M TiCl4 solution before growing the NWs. Such a layer not only prevented electrical shorting in DSSCs but also enhanced the density, and ultrafine square NWs ranging from 10 nm to 35 nm were obtained, as shown in Fig. 8.4. TiO2 NWs/NRs can also be grown on FTO glass without seed layers. Aydil and Liu developed a facile, hydrothermal method for the first time to directly grow oriented, single-crystalline rutile TiO2 NR films on FTO substrates (see Fig. 8.4) [18]. A seed layer is not necessary because there is a small lattice mismatch between the FTO substrate and rutile TiO2, which plays a key role in driving the nucleation and growth of the rutile TiO2 NRs on FTO.

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