Research On Electric Desorption Properties Of Dye Molecule Fixed On The Interface Of Nanoporous TiO₂ Film

Dye-sensitized solar cell?DSSC?has been a hot topic in new energy field since it is introduced.Dye-sensitized film inside the device is the core component of DSSC in photoelectric conversion process,and the adsorbed dye amount of film surface is the key factor influencing the quality of sensitized film.The traditional method of measuring or controlling the adsorbed dye amount is to wash or soak sensitized film in desorption solution and indirectly control desorption process by controlling the condition such as concentration,soaking time,etc.,which is difficult to precisely intervene the dye desorption rate.An important problem of hindering the DSSC marketization is the poor long-term stability,and a large number of research results indicate that DSSC instability is caused by Dyed-TiO₂/EL interface,but there is still no a conclusion.Based on this situation,the paper conducted researches on electric desorption kinetics,electric desorption mechanism,quantitative desorption of the adsorbed polypyridyl ruthenium based dye molecules under the electric field action,as well as cell stability and extending cell life by the reconfiguration of the Dyed-TiO₂/EL interface on the electric desorption technology.Firstly,we explored the impact of different applied voltage,film thickness and desorption solution concentration on electric desorption dye properties,and the results suggested that electric desorption was an effective means of accurately and directly controlling the adsorbed dye amount on film surface.According to the Langmiur isothermal adsorption theory and the quasi-first-order reaction kinetics equation,the dye desorption rate k_d was 6.92×10^-3 s^-1 under the effect of-0.6 V.Meanwhile,the two possible dye desorption mechanism were inferred by means of Cyclic voltammetry scanning and UV–Visible absorption spectroscopy test technology:one was the fracture of ester bond between the dye molecules and TiO₂ under negative potential;another was the electrostatic repulsion desorption mechanism.Moreover,dye desorption was more likely to occur if the deprotonation reaction happen simultaneously in the latter mechanism.Secondly,this paper used electric desorption technology to in-situ erase dye on the anode surface and re-sensitize it again,refurbishing light anode,and studied cell macroscopic photoelectric properties,microscopic surface state,electron transfer and transport performance under the condition of continuous electric erasing/re-sensitization.Results showed that after continuous electric erasing/re-sensitization,the photoelectric conversion efficiency still remained at around 90%compared to initially prepared cell.The slight drop of J_sc and V_oc was the main factor of causing efficient decline.Through EIS analysis,the increasing surface defects of the film and the decreasing electron transport by electric erasing process were the main reason for the decline of J_sc,while the decrease of the electron transfer impedance led to the decrease of V_oc.Finally,after the assembly of DSSC devices lasted for about 700 h,in-situ electric erasing method was used to reconstruct the Dyed-TiO₂/EL interface,and the results showed that the photoelectric conversion performance of cell could be regenerated.EIS analysis confirmed that the change of the Dyed-TiO₂/EL interface was the origin of performance attenuation.The work of this paper provides theoretical guidance for synthesizing new dyes,clarifying the self-assembly mechanism of dyes,enhancing cell stability and improving cell efficiency.In particular,it makes DSSC no longer a disposable cell and the cell life is expected to be multiplied,which has certain practical significance.