Titanium Dioxide Nanoarray And Its Application In Flexible Dye-sensitized Solar Cells

Owing to the long-term use of fossil fuels, the crises of environmental pollution and resource depletion have becoming severely. The worldwide demand for clean energy is very urgent. As the origins of everything, solar energy has advantages such as powerful, sustainable, inexhaustible, etc. Photovoltaic is the important form of solar energy utilization. Dye-sensitized solar cells（DSSCs） have been regarded as one of the most promising alternatives for silicon-based solar cells due to their low manufacturing cost, great stability and outstanding power conversion efficiency（PCE）. Moreover, flexible and wearable electronic devices will be predominating in modern electronics. Therefore, lightweight and flexible DSSCs have attracted extensive scientific research interests in recent years. On this basis, this paper has studied the TiO₂ nanoarray and its application in flexible dye-sensitized solar cells.Firstly, oriented single-crystalline rutile TiO₂ nanowires（NWs） were converted to TiO₂ nanotubes（NTs） by a hydrothermal selective etching strategy. The surface area of the obtained TiO₂ NTs is several times more than that of the initial TiO₂ NWs. Within DSSCs application, the as-prepared TiO₂ NTs have achieved 112.5% enhancement in PCE than the initial unetched NWs.Secondly, a novel bi-layered TiO₂ nanostructure made of hierarchical NT（HNT） array as the bottom layer and P25 nanoparticles（NPs） as the top layer has been fabricated. Such bi-layered photoanode exhibits complementary and synergistic properties, in which the HNT bottom layer can provide the direct electron transport pathway, and the P25 top layer offer large surface area to adsorb more dye molecules. In addition, this bi-layered photoanode with a thickness of ²2 μm can more effectively harvest incident light. Therefore, the DSSC based on such a bi-layered photoanode achieved a remarkably enhanced PCE of 7.25% compared to the DSSC solely composed of P25 NPs（5.50%） or HNT arrays（5.08%）.Thirdly, a thin, lightweight and flexible mesh based DSSC has been developed by using anatase TiO₂ hierarchical NW（HNW） arrays as photoanode. A two-step hydrothermal method is used to synthesize the TiO₂ HNW arrays, which achieved a higher PCE of 1.76% within DSSC than generally electrochemical anodized TiO₂ NT arrays（1.52%）. The as-fabricated DSSC has good flexibility and fatigue resistance. It can be integrated to light up a group of green-light emission diodes, which demonstrated that the mesh based DSSCs are promising candidates for wearable energy supply devices.