Study On Photoelectric Properties And Their Magnetic-field Regulation In Dye Sensitive Solar Cells With Perovskite Manganese Oxide Electrodes

In recent years,in order to improve the efficiency of Dye-sensitized solar cells（DSSCs）and reduce the cost of cell preparation,a variety of semiconductors with unique band structure have been used as alternative materials for Pt counter electrodes（CEs）.At the same time,the photoanode optimization method of new composite materials by doping and modification is also presented.In this paper,the material of perovskite manganese oxide was applied to DSSCs,and based on the ponton magnetoresistance effect（CMR）of its special mechanism,the response of the photoelectric performance of the battery under the action of external magnetic field was studied and the regulation mechanism of magnetic field on the DSSC was discussed.It is found that perovskite manganese oxide can be used as CEs material of DSSCs,and can also be used as doping modification material in photoanode,realizing the positive modulation of cells current and efficiency by external magnetic field,and improving the photoelectric performance of the cells.The specific works is as follows:First,the La_0.67（Ca Ba）_0.33MnO₃（LCBMO）counter electrodes were prepared by combining sol-gel method and pulsed laser deposition method,and the Photoelectric conversion efficiency of DSSCs up to 1.49%was obtained.The optoelectronic properties of DSSCs were tested under magnetic fields of 0T and 0.25T.When the applied magnetic field is 0.25T,the stability of short-circuit current density and photoelectric conversion efficiency of DSSCs is better than that of the DSSCs tested without external magnetic field.Further results showed that both the exchange current density and the limiting diffusion current density were larger than the corresponding parameters of the DSSCs without suffering external magnetic field treatment.Besides,the fitting results of electrochemical impedance spectroscopy also present that the interface impedance value of the DSSCs is smaller when under the external magnetic field.Therefore,the resistance of the LCBMO counter electrode can be reduced under external magnetic field,and the attenuation of photoelectric conversion efficiency can be slowed down by applying a magnetic field.Secondly,the material La_0.67Sr_0.33MnO₃（LSMO）,which can exhibit more obvious colossal magnetoresistance effect at room temperature,was selected as the counter electrode of DSSCs,in which more obvious response of the photoelectric performance to external magnetic field may be observed.Here,the LSMO counter electrode was prepared by PLD method,and the photoelectric conversion efficiency of the DSSCs up to 2.71%was obtained.Under a magnetic field of 0.25 T,the J₀ and J_lim of LSMO counter eletrode were significantly larger than those of the counter eletrode without suffering external magnetic field treatment,and the increase was more obvious than that of LCBMO counter eletrode under the same measurement conditions.Compared with those parameters obtained without external magnetic field,the fitting results of electrochemical impedance spectroscopy also show that the value of interface impedance decreases by 15.55Ω/cm².At this time,the attenuation degree of the short-circuit current density and the photoelectric conversion efficiency of cells became smaller,and the photoelectric properties of the DSSCs present more stability.In conclusion,the effect of external magnetic field on the resistance of LSMO counter electrode is more obvious than the effect in LCBMO counter electrode,and the optoelectronic properties of DSSCs with LSMO counter electrode can be optimized by external magnetic field.Finally,considering that the band gap of LSMO is in the range of 1.0～1.2e V,and the Fermi energy is about 4.8e V,which meets the requirement of energy level matching with dyes.The unique electronic structure and twisted rhombohedral perovskite structure in LSMO are beneficial to the separation of positive and negative charges,and moreover,LSMO can exhibit colossal magnetoresistance effect at room temperature,one can think that the application of LSMO to photoanode can provide a new idea for the regulation of the photovoltaic performance of DSSCs by an applied magnetic field.Here,The LSMO nanoparticles and TiO₂ particles were prepared into composite materials and applied to the photoanode,and then tested under the conditions of 0T and 0.25T external magnetic field.By changing the content of LSMO,the short-circuit current density and Photoelectric conversion efficiency of the dye-sensitized solar cells with a small amount of LSMO doped TiO₂ photoanode began to recover after 300s.However,the short-circuit current density and photoelectric conversion efficiency of pure TiO₂ photoanode in DSSCs continue to decline with time.Surprisingly,when the applied magnetic field is 0.25T,the short-circuit current density and photoelectric conversion efficiency of the DSSCs start to recover after200s,and even exceed the initial measured values after 400s.It can be seen that a small amount of LSMO is beneficial to slow down the efficiency decline caused by the long-term use of the cells,and an external magnetic field can realize the positive regulation of the photoelectric performance of the DSSCs with LSMO/TiO₂ as photoanode,and then improve the efficiency of the cells.