A Study On The Mechanism Of Multi-recombination Source In Dye-sensitized Solar Cells

As a new type of solar cell, Dye-sensitized Solar Cells(DSC)have attracted general attention for its unique structure and low manufacturing cost. The photoelectric conversion efficiency of DSC can approach to 13%, showing vast application prospects.The main reason of the cell energy loss is the recombination process occurring at the interface in DSC.The recombination process mainly occurs in the contact interface between TiO2 semiconductor film and electrolyte(Dyed-TiO2/EL interface) which includes several of electronrecombination sources. Additionally, DSC has another interface where the recombination process occurs. That is the interface between the conductive glass andthe electrolyte(TCO/EL interface).The recombination process occurred at the Dyed-TiO2/EL interface has been researched in depth. However, there are still a lot of controversies to the recombination process of TCO/EL interface and that whether the TCO/EL interface has significant effect on the overall recombination process of DSC.Therefore, this article intends to solve this controversial issue by investigating the recombination mechanism in depth from the perspective of two interfaces and multiple recombination sourcesand clarifying the recombination process of TCO/EL interface and reveling the influence of TCO/EL interface on the whole recombination process of DSC with the electron lifetime.Firstly, based on the equivalent circuit theory and Marcus theory, and in consideration of conduction band states, exponentially surface states and monoenergetic surface states in the Dyed-TiO2/EL interface, the article established the electron lifetime model of multi-recombination source on a single interface.Then, on the basis of this model,we establish a relatively complete electron lifetime model with multi-recombination source in two interfaces based on the Volmer-Buttler theory and in consideration of the characteristics of the TCO/EL interface and the microstructure of TiO2 film.Secondly,based on the electron lifetime model of multi-recombination source in single interface, the effects on electron lifetime of these parameters including the effective density of states N, the electron-transfer rate k and the recombination energyλare were investigated by changingthem in a wide range. The results reveal the formation law of the electron lifetime curve which recombination by the Dyed-TiO2/EL interface,the characteristics of the electron lifetime curve of each recombination source and its contribution to the electron lifetime curve.Thirdly, based on the electron lifetime model of multi-recombination source in two interface, we researched the effects of Dyed-TiO2/EL interface and TCO/EL interface on the recombination process of DSC.It turns out that due to the involvement of the TCO/EL interface, it would disturbthe characteristic curve of the recombination sources in the Dyed-TiO2/EL interface so that the electronrecombination source could not be judged by the characteristic of the electron lifetime curve, which solves the controversies in previous articles. Meanwhile, the article points out the view that the method of using deposit blocking layers in the reference could not simply eliminate the interference of TCO/EL interface.Finally, this article summarizes the full text and makes a prospect on the further that improvement of the electronic lifetime model with multi-recombination source in two interfaces.The research in this article provides a theoretical guidance in the understanding of the working mechanism of the DSC, improving the efficiency of the battery photoelectric conversion, and reducing the energy loss.