Research On Dye Sensitized Solar Cell Co-sensitization System And Photoanode Material

In order to alleviate the problems of air pollution and energy shortage, researchers have begun to take attention to clean solar cells. Dye-sensitized solar cells （DSSCs） become an active field because of their easy fabrication process and low costs. The typical DSSC is consisted of three components:a photoanode （porous semiconductor oxide films with dyes）, an electrolyte, and a counter electrode. As the key components, which their performance have obvious influence on the power conversion efficiency of DSSCs. To date, DSSCs based on single dye sensitizer is difficult to provide better light-harvesting ability. In order to widen the light absorption range, two or more dyes sensitizers are used together to achieve DSSCs panchromatic light harvesting. However, much more factors should be thought to affect the power conversion efficiency in the co-sensitized systems, not only the the absorption spectra, but also the molecular sizes, the dye loading modes and the contribution of sensitizers and co-sensitizers on efficiencies of co-sensitized devices. In our work, comprehensive investigation has been realized.The photoanode has two main functions:loading dyes, which is the carrier of sensitizers; convoy electrons. So it is important for the DSSCs. Porous TiO₂ films have been used widely due to their superiorities. Such as extreme stable, inexpensive, simple preparation, larger specific surface area and so on. TiO₂ films have one shortage: the thickness of TiO₂ films increase to a degree, there are some influences on the transmission of electrons. In this paper, we preliminary study on improving the dye loading on TiO₂ films with limited thickness to improve the power conversion efficiency.Details are as the follows:（1） To improve the fabrication of DSSCs. Through screening the thickness of TiO₂ films, the different scattering layer and so on. Finally, the PCE of dye N719 from 6.50% to 7.80%, and AZ260 from 6.69% to 6.94%.（2） Two organic dyes （T-CO and D-0） with different molecular size as co-sensitizers have been investigated to fabricate co-sensitized solar cells （AZ260/T-C0 and AZ260/D-0）. Their match of molecular size, light absorption, and dye-loading modes were conducted by density functional theory （DFT）, UV-Vis absorption spectra and TGA/HPLC methods. All of the results were correlated with the PCE of the cells. We proposed an effectiveness of co-sensitizers （Ecs）, which could be ascribed by two dye-loading modes between sensitizer and co-sensitizer, i.e. side-by-side adsorption and complementary adsorption on the TiO₂ film. Calculated Ecs values show that T-CO molecules are predominant over a side-by-side mode as co-sensitizer while D-0 molecules are predominant over a complementary one and the excess of the dye molecules only act as co-adsorbents to fill up the blank of TiO₂ surfaces.（3） Making the pastes which contain P25 powder and carbon nanosphere with the different manufacture methods of photoanode, the PCE of dye N719 from 7.84% to 8.63%, finally.