| Dye-sensitized solar cell (DSC) regarded as the third generation solar cell is promising due to its low cost and high theoretical efficiency. Flexible DSC shows much more potential for its lightweight and flexibility. However, up to date the preparation of TiO2 film of flexible DSC at low temperature is complex and the efficiency is poor because of the poor connections between TiO2 nano-particles. Graded structure composed of different sized nano-particles without any organic binder is a porous structure and has good mechanic performance. When chemical bonds are used as the connection between nanoparticles, the electron transport in this graded structure will be fast enough for DSC. Such graded structure is promising for flexible photoanodes of DSC if prepared at low temperature. In addition, there are some defects on TiO2 surface which would lead to the electron recombination at TiO2/electrolyte surface. Passivating these defects with some adsorbents may keep oxide species away from the defects and reduce the electron recombination, which will improve the photovoltaic performance and long term stability of DSC. In this thesis, the preparation of binder-free paste, low-temperature sintering technique and a new flexible photoanode with graded-particle-structure will be developed. The effect of the structure of the photoanode on the performance of DSC, such as the transport and the recombination of electrons, would be studied. New coadsorbents would be designed and synthesized to improve the I-V performance and long term stability of DSC.Different sized nano-particles were synthesized by hydrothermal method and binder-free paste was prepared. Flexible graded TiO2 film was fabricated by doctoral blade method and the sintering method were explored. The effect of the ratio of nano-particles on the photovoltaic performance was scrutinized. What is more, the effect of the structure properties, such as porosity, specific surface area and mean pore size, on the operation of DSC was also determined. The optimum film was obtained and the highest efficiency was 4.54%. The effect of carboxyl coadsorbents, pivalic acid and 3, 3-dimethylbutanoic acid, on DSC was studied. The results showed that different coadsorption conditions affect the performance obviously. The coadsorption of the carboxyl acids can improve the photovoltaic performance of DSC greatly. The transient spectra results revealed that the coadsorption of carboxyl acid can passivate the TiO2 surface and shift the band edge of TiO2 negatively. In addition, the pivalic acid improved the long term stability a little bit.Based on the research on carboxyl acids, phosphinic acids, dimethylphosphinic acid and dineohexylphosphinic acid, were also synthesized and applied to DSC as coadsorbents. The results presented that phosphinic coadsorbents can improve the photovoltaic performance greatly even better than carboxyl acids. The transient experiments proved that phosphinic acids could passivate the TiO2 surface and shift up the band edge of TiO2 in the same way that carboxyl acids could. More importantly, the DSCs coadsorbed with phosphinic acids show excellent long term stability than the DSCs with carboxyl coadsorbents. It is exiting for the application of DSC in the near future. In addition, dineohexylphosphinic acid was also used in flexible photoanodes and better photovoltaic performance was obtained.
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