Studies Of Dye-sensitized Solar Cells Based On Natural Dyes

Dye-sensitized solar cell (DSC) is a new class of green photovoltaic cell based on photosynthesis principle in nature. It has attracted much attention since 1991 for its simple preparation procedure, low cost, stable photo-to-electric performance and friendly environment action, which make it a good alternative to photo-to-electric devices. And it is considered a landmark in the research of solar cell. However, the photoelectric conversion efficiency of DSC is somewhat low in comparison with the silicon solar cells, who has taken up the most part of the current market. So it's very important to further improve the photo-to-electric conversion efficiency of DSC. In this paper, the selection of sensitizers and the optimization of the carbon electrode were investigated to improve the photoelectric conversion efficiency of DSCs.(1) We fabricated the DSCs using twenty natural dyes as sensitizers, which were extracted from the materials existing in nature and our life, such as flowers, leaves, fruits, traditional Chinese medicines and beverages. The extracted dyes were characterized by UV-Vis absorption spectra. The photoelectrochemical performances of the DSCs based on the dyes showed that the open circuit voltages (Voc) varied from 0.337 V to 0.689 V and the short circuit photocurrent densities (Jsc) were in the range of 0.14-2.69 mA cm-2. Especially, the Voc of DSC with mangosteen pericarp extract as sensitizer is 0.686 V, comparable with that of the Ru complex N719. The photo-to-electric conversion efficiency of the DSC sensitized by the mangosteen pericarp extract without any purification reached 1.17%. Moreover, the various components of mangosteen pericarp dye were extracted using different organic solvents step by step. The photoelectrochemical performance of the extracts exhibited that the main effective component as sensitizers for the DSCs was rutin.(2) As an important part of DSC, the counter electrodes have an important impact on the the photoelectric conversion efficiency of DSC. Pt is widely used in DSC as the material of counter electrode for its good and active catalysis as well as its stability in the electrolyte. The sputter method is widely used for preparing the Pt counter electrode. However, it is difficult to industrialize for the restriction of the equipment. Thereby, the optimumzation of the technics was carried out to get a higher conversion efficiency by using less load of Pt. The Pt counter electrodes were prepared by several different processes and the result shows that the performances of Pt counter electrodes prepared by our methods are similar to the Pt counter electrodes prepared by the sputter methods. Although the high efficiency was gotten, Pt is a precious metal and it will increase the production costs of DSCs by its high price. Carbon materials aroused people's interests for its good electronic conductivity, stable performance, high catalytic activity and low cost. In this paper, three different methods of preliminary preparation of carbon counter electrodes were introduced, and the performances were tested. Last, a better method with low cost to preparing the carbon counter electrode was confirmed.