Synthesis Of Down Conversion Materials And Their Application In Novel Solar Cells

Perovskite solar cell(PSC)as a new type of solar cell has the advantages of low production cost,simple preparation,high mobility and absorption coefficient.It has become a major innovation in solar technology.Due to the limitation of the band gap width,the conventional PSC can only absorb about 44%of the total solar radiation spectrum in visible light,which leads to the energy loss of the incident sunlight and also the efficiency is limited.Moreover,the UV light with higher energy,will cause a damage to the structure of PSC,resulting in a decrease in photoelectric properties.Although the use of a UV cut-off filter could avoid the damage and improve the PSC stability,but it also causes the ineffective utilization of UV light,and reduces the efficiency of light collection.In order to improve the efficiency and stability of PSC,we use down-conversion material to extend the spectral response range of PSC and decrease the UV induced degradation.As a kind of excellent luminescent materials,rare earth complexes have the advantages of high luminous efficiency,wide absorption range and long fluorescence lifetime,which is good for improving the light utilization efficiency and performance of PSC.In this thesis,we tried to improve the luminescent properties of the complexes and systematically studied the relationship between the down-conversion luminescence of the complexes and the performance of PSC.In addition,the combination of Eu3+ ions with high quantum efficiency can be used to further reduce the UV induced degradation and improve the efficiency of the TiO2.In order to improve the luminescent properties of europium complexes,we employed different content of ethylenediamine in Phen-Eu(?)system to modify the coordination environment around Eu3+ ions.It was found that when the content was 0.2 mmol,the complexes showed great luminescent properties.However,excess ethylenediamine might hinder the coordination between Phen and Eu3+ ions,leading to the decline of luminescent.Luminescent properties of complexes with different substituents(5-nitro,5-methyl,4,7-dimethyl,4,7-dimethoxy and 4,7-diphenyl)connected on the benzene ring of Phen were discussed.The results showed that electron donating groups and the conjugated groups can improve the electron cloud density of the complexes,decrease the level of the electron transition,and increase the UV absorption coefficient of the complexes.Moreover,the substituent effect and conjugated effect is helpful to improve the matching degree between the level of luminescence center and ligand,effectively increase the intramolecular energy transfer efficiency,which laid a foundation for its application in PSC.According to the analysis on the luminescence properties of the complexes,complex with high UV absorption ability and strong luminous intensity was selected as the light down-conversion layer(LDL)to be used in PSC.The PSC with LDL showed 11.8%current gain and after 10 h UV irradiation,it still has 74%of initial efficiency.To improve the utilization rate of UV light and further reduce the UV induced degradation in PSC,we have prepared Eu doped TiO2down-conversion luminescent material(TiO2:Eu3+)as mesoporous layer in PSC.The results of SEM?XRD?XPS and PL showed that Eu3+ ions were not in the TiO2 lattice,but attached to the surface of the TiO2,which was help to suppress compound between electron and hole,causes the increase of open circuit voltage.In addition,TiO2 could induce the Eu3+ ion to emit red light and realize the effective UV light utilization of PSC.Meanwhile,the oxidation-reduction of electron hole pair caused by TiO2 was reduced,so that the PSC can obtain higher efficiency and UV stability.However,excessive doping of Eu can increase the grain boundary defects of TiO2,and the probability of electron-hole recombination in TiO2 and CH3NH3PbI3 becomes larger,which is not conducive to electron transport in TiO2.