Investigations Of Photophysical Processes For Organic Solar Cells

Because of the advantages of its clear, flexible and easy to be produced in large-scale, Organic solar cells become the focus in new energy area. But to make it to be a low cost, competitive, alternative green energy, a breakthrough in photoelectric conversion efficiency should be made first. In organic solar cells, the recombination of exciton is an important influence factor of photoelectric conversion efficiency. For insight into the photo-induced electron transfer mechanism in organic solar cells, in this work, based on Marcus theory on electron transfer, we investigate the photo-induced electron transfer from oligothiophenes to fullerenes via fluorescence quenching. The major research and innovative results obtained are as follows:(1) In our study, since the absorption spectra of oligothiophenes and fullerenes are overlapping, the inner-filter effect leads to an unrealistically high ratio of fluorescence quenching. Therefor, the experimental data can not be a true reflection of the degree of fluorescence quenching, and thus the efficiency of electron transfer in donor-acceptor system will cannot be properly analyzed. In order to obtain the quenching ratio which can reflect the efficiency of electron transfer realistically, an original correction method is developed via setting up a physical model of absoption of binary system, to remove the affects of the inner-filter effect. This study also provides a new way for solving the general problem of the inner-filter effect.(2) Fluorescence quenching is a macro phenomenon of electron transfer in donor-acceptor system, so, the efficiency of electron transfer from oligothiophenes to fullerenes can be studied by fluorescence analyzing. With our correction method, the fluorescence quenching of oligothiophenes(3T～7T) /fullerenes(C₆₀,C₇₀,C₈₄) mixtures in solution is studied systemly, and the results show that the electron transfer in oligothiophenes / fullerenes mixtures is clearly dependent on the chain length of oligothiophene and the electron affinity of the fullerenes. Meanwhile, according to Marcus theory on electron transfer, the change in Gibbs free energy for charge separation is also studied, and the results based on Weller equation are in full agreement with above conclusions.(3) To understand the influence of substituents on electron transfer, terthiophene with substituents (3P) is analyzed via fluorescence quenching, the results show that the efficiency of electron transfer from 3P to fullerenes also depends on the electron affinity of fullerenes. Compared with the reference material (5T), the fluorescence quenching ratios have risen, but the absorption and intrinsic fluorescence intensity decreased. This study has some significance to synthesis of organic photosensitive materials. (4) Manufacture technique of organic solar cells is the key to realizing the conversion from solar energy into electrical energy. In this paper, the preparation of organic solar cells based on oligothiophenes(6T,7T) and fullerenes(C₆₀,C₇₀) is explored, some interim progresses are obtained, and the practical experiences accumulated lay a foundation for further research..This research has been supported by the National Natural Science Fundation (No. 20573030).