Interfacial Electron Transfer Behavior And Regulatory Mechanism Of Dye-sensitized Solar Cells

Solar energy is one of the renewnable power sources featuring asclean,cheap,green,and abundant.Nowadays solar energy is primarily harvested by using photovoltaic cells.Dye-sensitized solar cells?DSCs?are one of the“third generation”organic photovoltaic cells.The devices show the advantages of low cost,easy-fabrication.Researches on this issue are still going.However,charge separation and transport in dye-sensitized cell is so sophisticated,which makes the mechanism of charge separation behavior at the TiO₂ interface is not fully understood.Particularly,the effect of sensitizers on charge recombination reaction remains controversial.Therefore,this thesis focuses on elucidating the role of sensitizers in reducing the charge loss at TiO₂ surfaces by using dye desorption technique.At the same time,the feasibility of renewing the photovoltaic property of partly desorbed TiO₂ film is also investigated..Self-assembly of organic sensitizer layer in cobalt complex based DSCs was studied for uncovering its role in reducing the loss of charge recombination.The DSCs with various dye loading was fabricated by dye desorption without the help of basic solvent.The FT-IR and UV results indicate the deprotonation of the anchoring organic sensitizers,which influences the conduction band of TiO₂ remarkably via the variation of surface potential.Positive band edge shift and the decrease ofrecombination rate constantare demonstrated as the main factors for energy loss at open circuit.By contrast,the analyses on absorbed photon conversion efficiency?APCE?illuminate the crucial role of the packing of the anchoring sensitizer in reducing recombination loss at short circuit.This is further supported by the numerical simulations,which show the APCE is primarily dependent of the recombination rate constant rather than the band edge shift at short circuit.These results highlight the self-assembly of the sensitizers with insulating groups in retarding charge recombination by forming overlapping molecular layer.The TiO₂ films after desorbing a part of sensitizers are treated with chenodeoxycholic acid?CDCA?as well as a series of silane molecules.In this way,the recovery of cell performance for partly desorbed TiO₂ films is evaluated.It is shown that both CDCA and silane molecules are capable of retarding electron recombination and hence improving photocurrent and photovoltage at different dye loading.Comparing the current-voltage response curves at various light intensities and incident power conversion efficiency,we found that the vacancies at TiO₂ film originating from dye desorption can be occupied by CDCA molecules.As a result,power conversion efficiency is improved because of the reduction of recombination rate.Moreover,the photocurrent response under high illumination intensity is opposite to that under low light intensity.According to the results of electrochemical impedence measurements,the introduction of CDCA leads to the dissociation of the anchoring sensitizers due to their competitive adsorption.It follows that the channels in nanoporous TiO₂ film for transporting cobalt complexes becomes narrower.Such limited diffusion is then expected to engender the reduction of photocurrent output.In addition,surface modification using silane molecules is shown to suppress the recombination reaction in TiO₂ films considerably.And the diffusion limitation is absent even the devices work under strong illumination.It indicates there is no competitive adsorption between sensitizers and silane molecules.And silane treatment could be valid in improving photocurrent.