The Research Of Photoelectron Transmission And Artificial Modulation In Nanocrystalline Titania Solar Cells

Dye-sensitized nanocrystalline solar cells have attracted more and more attention in academic and industrial areas, due to its high conversion efficiency, low cost, simple technology and environmental advantages. Nanoporous crystalline TiO₂ film electrodes are the crucial composition of dye-sensitized solar cells （DSCs）, which affect the adsorption of dye sensitizers, the transmission of sunlight, the diffusion and transport of photoelectrons.Currently, the international researches of dye-sensitized nanocrystalline solar cells mainly focus on TiO₂ and the new wide band gap semiconductor materials for replacement of ordinary TiO₂. Other semiconductor materials such as ZnO, SnO₂ and Nb2O5, also can be prepared as DSCs, however, their photoelectric conversion efficiency are far less than the conventional nano-TiO₂ solar cells. To improve the electronic transmission performance in the films and the efficiency of DSCs, a variety of methods for surface modification and cationic dopings are researched. Carbon nanotubes （CNTs） are frequently report to improve photoelectric conversion materials and devices as a new carrier transmission nano-material, because of the unique electrical properties caused by their electron quantum confinement effect, good electrical conductivity, chemical stability and absorb light.In this paper, it is demonstrated that the preparation process of TiO₂ photoanode on the DSCs photoelectric can affect the conversion efficiency. A unique parallel electric field treatment in addition to chemical surface modification are processed to improve the photoelectric conversion performance of the DSCs,. The main contents and results are as follows:1) By XRD, SEM, EIS and other testing methods, the effect of heat treatment on TiO₂ thin film is studied, and the influences of the photoanode thickness on the photoelectric conversion efficiency and the photoelectron recombination process are discussed with emphasis. The importance of the TiCl4 and large particles treatment in increasing the efficiency of DSCs is clarified. By optimizing the heat treatment process and film thickness, the high photoelectric conversion efficiency of obtained samples increase by 38.7% than the traditional pure TiO₂ thin films.2) By XRD, SEM, UV-visible absorption spectra and other testing methods, the characteristics of electrode materials after doping are clarified, and the effect of doping on the performance of DSCs is studied in detail by IMPS/IMVS and flatband potential measurement. The results show that CNTs don’t broaden the absorption spectrum and is also difficult to change the Fermi level of TiO₂. However, the efficiency of DSCs used by carbon nanotubes / TiO₂ composite thin film with appropriate doping （e.g. 0.05%） is improved, and then the conversion efficiency gradualy declines with the increase of doping content, because the doped CNTs enhances the electron transport, reduces the electron recombination rate. 3) The effect of parallel electric field treatment on the efficiency of DSCs doped 0.05% MWNCTs is studied by I-V measurement. It is demonstrated that the Jsc and FF increased significantly, and it improve the efficiency of DSCs from 4.28% to 5.15%, by an increase of 20%.4) By SEM, IMPS/IMVS, EIS and other testing methods, the physics mechanism of parallel electric field treatment is studied. It reveals that the electric field causes MWCNTs orientation order enhancement along the direction of electric field in the composite films. The electron transfer time becomes shorter, while the electronic life expectancy becomes longer. At the same time, the dyes | electrolyte | TiO₂-MWCNTs interface impedance becomes larger, and the charge recombination rate decreases. The dark current decreases, and the corresponding recombination rate becomes smaller as well.