Study On Preparation And Properties Of Dye-Sensitized Solar Cells(DSSCs) Based On Nanorod Arrays

In recent years, great progress has been achieved in Dye-sensitised Solar Cells (DSSCs). To date, DSSCs employing porous titania nanoparticles have shown the highest power conversion efficiency value over11%. To overcome the limitation of TiO2nanoparticles induced by the trap sites at the surface and the countless contact among the nanopaticles, DSSCs based on one-dimensional (1-D) nanostructures including nanorod and nanowire have attracted much attention. So far, there are lots of reports about TiO2nanoparticles but only a few about TiO2nanorod arrays, hence it is necessary to research TiO2nanorod arrays-based DSSCs systematically. In addition, Due to the similarity of the energy band gap and the electron-injection process of ZnO to that of TiO2, and its higher electronic mobility and easier synthetic process, ZnO has been expected to be compatible with TiO2as a working electrode in DSSCs.In this paper, oriented TiO2nanorod arrays and ZnO nanorod arrays have been successfully prepared on FTO substrates, respectively, and ZnO nanorods/nanoparticales and TiO2/ZnO hygid nanorods have also been fabricated.The properties of these nanostructures were characterized by XRD, SEM, XPS, and ultraviolet-visible spectrophotometer, and the properties of the DSSCs were investigated by current-voltage characteristics, IPCE spectra and IMPS/IMVS analyses.The main results are as following:①The tetragonal rutile TiO2nanorod arrays were prepared by hydrothermal method firstly using the solution containing the mixture of hydrochloric acid and glacial acetic acid, the nanorods are oriented along the [001] growth direction. Ti, O and C elements are observed in the nanorod array films.②The effect of the HO Ac content, the volume of TTIP, growth time and growth temperature on the properties of TiO2nanorod arrays and DSSCs has systematically investigated. It is found that with increasing the HOAc content, the nanorods gets thicker and longer firstly and then becomes thinner and shorter. The increase in the volume of TTIP made the nanorod grow taller, and then the area for dye adsorption was increased. The nanarods gradually separate each other with increasing growth temperature. With increasing HOAc content, TTIP content, and growth temperature, the DSSCs all shows the trend that the Isc and η increase first and decrease afterward. Prolonging the growth time has little effect on the length of the nanorods and the Isc and η of the DSSCs; increased growth times induces thicker nanorod films, however, the A: and77decrease with increasing the growth times. Take full consideration of all kinds of factors, the optimum preparation parameter for oriented, uniform, dense and longer nanorod arrays is obtained:TTIP:HC1:HOAc:H2O volume ratio0.8:4:8:8, growth temperature150℃, and growth time5h. The conversion efficiency of the DSSC based on2.24μm-TiO2nanorod array films grown under the above parameter is3.43%, with the pretreatment of the FTO substrate, the conversion efficiency is enhanced to4.03%.③As compared to the TiO2nanorods obtained from a single acid system, the nanorods prepared from a solution containing the mixed acids exhibited faster electron diffusion and higher dye loading, resulting in higher short-circuit photocurrent and power conversion efficiency.④The ZnO nanorod arrays prepared by two-steps chemical process are hexagonal wurtzite ZnO phase, and the nanorods are oriented along the [001] growth direction. Zn, O, C and Si elements are observed in the nanorod array films.⑤The effect of growth times and PEI on the properties of ZnO nanorod arrays and DSSCs has been studied. With increasing the growth times, the ZnO nanorods become longer, but not well orientied. The PEI added in ZnO sol or growth solution has no effect on the structure of ZnO nanorod array films. With adding the PEI in ZnO sol, the as-prepared ZnO nanorods were sparser and more oblique; while with PEI in the growth solution, the nanorods became smaller in diameter and longer in length. A η of2.30%had been achieved on a DSSC based on a7.9μm-long nanorod array film prepared by a growth solution containing the PEI.⑥ZnO nanorods/nanoparticales and TiO2/ZnO hygid nanorods have been prepared. Comparing to the single ZnO nanorods electrode, the properties of the DSSC based on hybrid ZnO nanorods/nanoparticles are slightly improved. The Isc is increased13%. Furthermore, comparing to the single TiO2nanorods electrode, the Isc of the DSSC based on hybrid TiO2/ZnO nanorods is dropped by87%, the Voc and FF are down by5.2%and14.6%, respectively, which leading to a great decrease (90%) of the η. Further investigation of the influence and mechanism of hybrid nanostructrues on DSSCs is required.