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Solution-Processed Anatase Titania Nanowires: From Hyperbranched Design to Optoelectronic Applications Wu-Qiang Wu, Yang-Fan Xu, Hong-Yan Chen, Dai-Bin Kuang,* and Cheng-Yong Su MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, Lehn Institute of Functional Materials, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, P. R. China
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CONSPECTUS: The utilization of solar energy and the development of its related optoelectronic devices have become more important than ever. Solar cells or photoelectrochemical (PEC) cells that require the design of light harvesting assemblies for efficiently converting solar light into electricity or solar fuels are of particular interest. Semiconductor TiO2, serving as the photoelectrode for photovoltaic devices (e.g., dye- or quantum dot-sensitized solar cells (DSSCs/QDSSCs) or perovskite solar cells (PSCs)) and PEC cells, has aroused intense research interest owing to its inherent characteristics of wide band gap and promising optical and electrical properties. TiO2 nanowires (TNWs) have been widely used in optoelectronic devices due to their unique 1D geometry and salient optical and electrical properties. However, the insufficient surface area resulting from the relatively large diameter of NWs and considerable free space between adjacent NWs restricts their optoelectronic performance. Hence, it is desirable to explore every feasible aspect of TNWs in terms of structural design and optical management, aiming to further improve the performance of optoelectronic devices. In this Account, we present a brief survey of strategies for designing branched or hyperbranched TNW-based photoelectrodes and their applications in solar cells and PEC cells. The general strategies (e.g., alkaline/acid hydrothermal method, lift-off transfer, and self-assembly approach) are discussed to address the challenges associated with fabricating TNWs on transparent conducting oxide (TCO) substrates. A series of strategies to fabricate judiciously designed 3D branched array architectures, including length tuning and sequential surface branched or hyperbranched modification, are proposed. The versatile implantation of the TNWs onto other backbones (nanosheets, nanotubes, hollow spheres, or multilayered electrodes) and substrates (fiber-shaped metal wire or mesh, flexible metal foil, or plastic sheet) is demonstrated to construct a new class of the TNW-embedded composite electrode materials with desired morphological characteristics and optoelectronic properties, for example, favorable energy level alignment for cascade charge transfer and rational homogeneous/heterogeneous interfacial engineering. The functionalities of TNW-based electrodes include enlarged surface area and superior light scattering for maximized light harvesting, as well as facilitated charge transport and suppressed charge recombination for enhanced charge collection, which are promising in optoelectronic fields such as solar cells, photocatalysis, and PEC cells. Beyond TNWs, one can also integrate other types of semiconductor (e.g., Fe2O3 or WO3) NWs into rationally designed structures for preparing novel photocatalytic materials with panchromatic absorption, efficient charge transfer, and excellent catalytic properties. Finally, an insightful perspective for rational design of advanced NW-based materials is provided. highly required.8 To date, most of the TiO2 nanowire (TNW) arrays fabricated on fluorine-doped tin oxide (FTO) glass were reported to be rutile TiO2 because of the very small lattice mismatch ( 17% Efficiency. Nano Energy 2017, 32, 187−194. (31) Wu, W.-Q.; Chen, D.; Huang, F.; Cheng, Y.-B.; Caruso, R. A. Sub-100 °C Solution Processed Amorphous Titania Nanowire Thin Films for High-Performance Perovskite Solar Cells. J. Power Sources 2016, 329, 17−22. (32) Butburee, T.; Bai, Y.; Wang, H.; Chen, H.; Wang, Z.; Liu, G.; Zou, J.; Khemthong, P.; Lu, G. Q. M.; Wang, L. 2D Porous TiO2 Single-Crystalline Nanostructure Demonstrating High Photo-Electrochemical Water Splitting Performance. Adv. Mater. 2018, 30, 1705666. (33) Wu, W.-Q.; Huang, F.; Chen, D.; Cheng, Y.-B.; Caruso, R. A. Thin Films of Dendritic Anatase Titania Nanowires Enable Effective Hole-Blocking and Efficient Light-Harvesting for High-Performance Mesoscopic Perovskite Solar Cells. Adv. Funct. Mater. 2015, 25, 3264−3272. (34) Wu, W.-Q.; Feng, H.-L.; Rao, H.-S.; Kuang, D.-B.; Su, C.-Y. Rational Surface Engineering of Anatase Titania Core−Shell Nanowire Arrays: Full-Solution Processed Synthesis and Remarkable Photovoltaic Performance. ACS Appl. Mater. Interfaces 2014, 6, 19100−19108. (35) Wu, W.-Q.; Feng, H.-L.; Rao, H.-S.; Xu, Y.-F.; Kuang, D.-B.; Su, C.-Y. Maximizing Omnidirectional Light Harvesting in Metal Oxide Hyperbranched Array Architectures. Nat. Commun. 2014, 5, 3968. (36) Rao, H.-S.; Wu, W.-Q.; Liu, Y.; Xu, Y.-F.; Chen, B.-X.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y. CdS/CdSe Co-Sensitized Vertically Aligned Anatase TiO2 Nanowire Arrays for Efficient Solar Cells. Nano Energy 2014, 8, 1−8. (37) Wu, W.-Q.; Chen, D.; Cheng, Y.-B.; Caruso, R. A. ThreeDimensional Titanium Oxide Nanoarrays for Perovskite Photovoltaics: Surface Engineering for Cascade Charge Extraction and Beneficial Surface Passivation. Sustainable Energy Fuels 2017, 1, 1960−1967. (38) Wu, W.-Q.; Xu, Y.-F.; Rao, H.-S.; Feng, H.-L.; Su, C.-Y.; Kuang, D.-B. Constructing 3D Branched Nanowire Coated Macroporous Metal Oxide Electrodes with Homogeneous or Heterogeneous Compositions for Efficient Solar Cells. Angew. Chem., Int. Ed. 2014, 53, 4816−4821. (39) Xu, Y.-F.; Wu, W.-Q.; Rao, H.-S.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y. CdS/CdSe Co-Sensitized TiO2 Nanowire-Coated Hollow Spheres Exceeding 6% Photovoltaic Performance. Nano Energy 2015, 11, 621−630. (40) Wu, W.-Q.; Wang, L. 3D Branched Nanowire-Coated Macroporous Titania Thin Films for Efficient Perovskite Solar Cells. Adv. Funct. Mater. 2018, 28, 1804356.
(41) Agosta, R.; Giannuzzi, R.; De Marco, L.; Manca, M.; Belviso, M. R.; Cozzoli, P. D.; Gigli, G. Electrochemical Assessment of the Band-Edge Positioning in Shape-Tailored TiO2-Nanorod-Based Photoelectrodes for Dye Solar Cells. J. Phys. Chem. C 2013, 117, 2574−2583. (42) De Marco, L.; Manca, M.; Buonsanti, R.; Giannuzzi, R.; Malara, F.; Pareo, P.; Martiradonna, L.; Giancaspro, N. M.; Cozzoli, P. D.; Gigli, G. High-Quality Photoelectrodes Based on Shape-Tailored TiO2 Nanocrystals for Dye-Sensitized Solar Cells. J. Mater. Chem. 2011, 21, 13371−13379. (43) Buonsanti, R.; Carlino, E.; Giannini, C.; Altamura, D.; De Marco, L.; Giannuzzi, R.; Manca, M.; Gigli, G.; Cozzoli, P. D. Hyperbranched Anatase TiO2 Nanocrystals: Nonaqueous Synthesis, Growth Mechanism, and Exploitation in Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2011, 133, 19216−19239. (44) Lee, D.; Rho, Y.; Allen, F. I.; Minor, A. M.; Ko, S. H.; Grigoropoulos, C. P. Synthesis of Hierarchical TiO2 Nanowires with Densely-Packed and Omnidirectional Branches. Nanoscale 2013, 5, 11147−11152. (45) Iacobellis, R.; Giannuzzi, R.; Grisorio, R.; Qualtieri, A.; Scarfiello, R.; Mannino, G.; Cozzoli, P. D.; Suranna, G. P.; De Marco, L. Tailoring the Nanostructure of TiO2 Photoanodes for Efficient Co(II)/Co(III)-Mediated Dye-Sensitized Solar Cells. Adv. Sustainable Syst. 2017, 1, 1700098. (46) Loiudice, A.; Grancini, G.; Taurino, A.; Corricelli, M.; Belviso, M. R.; Striccoli, M.; Agostiano, A.; Curri, M. L.; Petrozza, A.; Cozzoli, P. D.; Rizzo, A.; Gigli, G. Three-Dimensional Self-Assembly of Networked Branched TiO2 Nanocrystal Scaffolds for Efficient RoomTemperature Processed Depleted Bulk Heterojunction Solar Cells. ACS Appl. Mater. Interfaces 2014, 6, 5026−5033. (47) De Marco, L.; Manca, M.; Giannuzzi, R.; Belviso, M. R.; Cozzoli, P. D.; Gigli, G. Shape-Tailored TiO2 Nanocrystals with Synergic Peculiarities as Building Blocks for Highly Efficient MultiStack Dye Solar Cells. Energy Environ. Sci. 2013, 6, 1791−1795. (48) Ye, M.; Zheng, D.; Lv, M.; Chen, C.; Lin, C.; Lin, Z. Hierarchically Structured Nanotubes for Highly Efficient DyeSensitized Solar Cells. Adv. Mater. 2013, 25, 3039−3044. (49) Chu, L.; Li, L.; Su, J.; Tu, F.; Liu, N.; Gao, Y. A General Method for Preparing Anatase TiO2 Tree like-Nanoarrays on Various Metal Wires for Fiber Dye-Sensitized Solar Cells. Sci. Rep. 2015, 4, 4420. (50) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37. (51) Park, J. H.; Kim, S.; Bard, A. J. Novel Carbon-Doped TiO2 Nanotube Arrays with High Aspect Ratios for Efficient Solar Water Splitting. Nano Lett. 2006, 6, 24−28. (52) Cho, I. S.; Chen, Z.; Forman, A. J.; Kim, D. R.; Rao, P. M.; Jaramillo, T. F.; Zheng, X. Branched TiO2 Nanorods for Photoelectrochemical Hydrogen Production. Nano Lett. 2011, 11, 4978− 4984. (53) Pan, Z.; Qiu, Y.; Yang, J.; Liu, M.; Zhou, L.; Xu, Y.; Sheng, L.; Zhao, X.; Zhang, Y. Synthesis of Three-Dimensional Hyperbranched TiO2 Nanowire Arrays with Significantly Enhanced Photoelectrochemical Hydrogen Production. J. Mater. Chem. A 2015, 3, 4004− 4009. (54) Liu, C.; Tang, J.; Chen, H. M.; Liu, B.; Yang, P. A Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting. Nano Lett. 2013, 13, 2989−2992. (55) Xu, Y.-F.; Rao, H.-S.; Chen, B.-X.; Lin, Y.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y. Achieving Highly Efficient Photoelectrochemical Water Oxidation with a TiCl4 Treated 3D Antimony-Doped SnO2 Macropore/Branched α-Fe2O3 Nanorod Heterojunction Photoanode. Adv. Sci. 2015, 2, 1500049.
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DOI: 10.1021/acs.accounts.8b00476 Acc. Chem. Res. XXXX, XXX, XXX−XXX
