Novel Nanoscale Conducting Counter Electrode For Quantum Dot Solar Cells

Quantum dot solar cells(QDSCs)have attracted extensive interest all around the world due to their great advantages of facile preparation, good flexibility and low-cost, and have become a new hot research. To date, the efficiencies of such devices are still low, and the development of QDSCs is still in its start-up stage. Most of reports based on quantum dot solar cells have still suffered low efficiency about 1%- 6%, typically around 3%, far less than the limit of single hetero junction solar cell efficiency. On the one hand, as a conventional method to fabricate metal counter electrodes, vacuum evaporation requires large amounts of energy, and what’s worse, the product prepared by vacuum evaporation can’t show fine mechanical properties or excellent crystal shapes due to the poor connection in the particle boundary, which leads to poor contact between the electrode and the photosensitive layer. On the other hand, quantum dots can’t match to the n-type semiconductor material best due to it’s narrow absorption band, which also limits the efficiency enhancement of QDSCs. Therefore, it is necessary to synthesis low-cost and good conductivity counter electrodes and broaden the absorption spectra of quantum dots. For these two problems, this paper has carried out the following innovative works.(1) A Cobalt-Ruthenium(Co-Ru) alloy nanofiber electrode has been successfully developed via hydrothermal method, which is a good way to synthesis electrodes with high specific surface area, excellent electrical performance, tight contact interface and good stability. Moreover, we successfully synthesize the CdS colloidal quantum dots with tunable absorption edge in aqueous phase. By optimizing the synthesis condition, high quality CdS quantum dot with high productivity and wide absorption band can be obtained. When evaluated as electrode materials of QDSCs, the photoelectric conversion efficiency of Co-Ru alloy electrode can reach 3.04%, much higher than that of Co(1.97%) or Ru(1.31%). This work indicates that the charge transfer resistance of Co-Ru alloy electrode is lower than that of pure Ru or Co metal electrodes. Additionally, alloy can significantly improve the photoelectric conversion efficiency of QDSCs due to its collaboration effect.(2) A Nickel-Ruthenium(Ni-Ru) alloy and pure Ni、Ru counter electrode have been successfully developed via hydrothermal reaction. The electrochemical properties of counter electrode and the efficiencies of fabricated QDSCs devices are studied systematically. Moreover we successfully synthesis the CdSe colloidal quantum dots via oil phase, and we obtain QDs with broad absorption spectrum and high quantum yield by optimizing the operation condition. The quantum dot solar cell was fabricated and the photoelectric property had been studied.(3) Graphene was synthesized by mechanical exfoliation approach. Graphene counter electrode was fabricated by a low-temperature spin-coating method. We research the influence of spin-coating process and grapheme film thickness on the photoelectric conversion efficiency of QDSCs by electrochemical method such as electrochemical impedance spectroscopy and Tafel polarization curves.