Synthesis of Fluorine-containing Polymers and Its Application in Perovskite Solar Cells
Author:Liu Hong Zhu
Supervisor:bian ji ming
The energy crisis has been the root issue hampering the development of human society,while the effective development of new energy sources such as solar cells is one of the effective methods to solve the energy crisis.In recent years,the represented MAPbI3-based metal halide perovskite materials has been regarded as a kind of ideal solar cell materials due to the advantages of the simple growth process,wide spectral absorption range and high defect tolerance.Perovskite solar cells(PSCs)based on the perovskite materials have a huge application prospect.In the past few years,the photoelectric conversion efficiency of PSCs increases from 3.8%to over 23.0%,which was comparable to the efficiency of currently commercial polycrystalline silicon solar cells.Whereas,the stabilities of this kind of battery are very poor under the environment of high temperature,high humidity and UV light,which become the biggest obstacle to restrict its application.Some traditional polymers could improve the stability and efficiency of PSCs when used in the interface of battery as modification layer,but the material itself remains unstable and limit its prospect.Fluoropolymers possess many excellent properties,such as water-repellent,oil-repellent,heat resistance,and chemical corrosion resistance,and fluoropolymer film can be easily formed by spin coating,compatiable with regular PSCs process.So the fluoropolymer can be expected to significantly increase the photoelectric conversion efficiency and long-term stability of PSCs device by interface modification and protection for the perovskite active layer.This paper carried out a series of research about the synthesis of new fluorinated polymers and their related application issues in PSCs,the main research contents and results were as follows:(1)The fluoropolymers with excellent properties are especially suitable for the modification materials of PSCs,but the related applications were seldom reported.The fluoropolymers used theoretically in PSCs should have higher hydrophobicity and heat resistance.Therefore,the hydrophobic organic fluoropolymers(HOFP)of three different types(low-fluorine,containing quarterary ammonium salt emulsifier,high-fluorine)were synthesized by semi-continuous emulsion polymerization with fluorine monomer of chlorotrifluoroenthylene and fluorine-containing acrylic monomers.The relationships of polymer composition,monomer proportion,structure and polymer physical properties were investigated systematically.The kinetics of emulsion polymerization was also analyzed and studied.The hydrophobicity and heat resistance of the different kind of fluoropolymers were emphatically studied for exploring more adoptable HOFP for PSCs.(2)MAPbI3-base perovskite solar cells(PSCs)was fabricated througth two-step spin coating method,while the fluoropolymer as functional layer was inserted into the different interface layers of PSCs for modification.The influence of HOFP introduced between different functional layers on integrated photovoltaic properties of PSCs was investigated systematically,and then the optimal structure of the modified PSCs by use of HOFP was obtained.The results established that the fluoropolymer could promote the efficiency of the cells when inserted between perovskite active layer and hole transport layer(HTL),and battery efficiency can be improved by more than 10%compared to the unmodified battery.The hysteresis effect of the cells has also been inhibited obviously.(3)Based on above research results,hybrid(FAMA)Pb(IBr)3-based perovskite solar cells were grown by anti-solvent method,and a novel-structure PSCs device was obtained througth inserting HOFP between perovskite layer and HTL.The influence of thickness of HOFP layer on integrated photovoltaic characteristics and environmental stabilities was studied,and so the optimal photoelectric conversion efficiency and stability were achieved.The results showed that the modified PSCs device by optimized HOFP process obtained photoelectric conversion efficiency(PCE)of 16.9%,open circuit voltage(Voc)of 1.14 V,short circuit current(Jsc)of 22.47 mA cm-2,and fill factor(FF)of 66%without encapsulation.Especially,the device stability had been greatly increased,the photoelectric conversion efficiency could maintain more than 80%of the initial efficiency after 100 days airtight storage.In summary,this paper mainly dealt with the preparation methods of water-based fluoropolymer,polymerization kinetics and the related research on fluoropolymer used in PSCs.The research results provided a new strategy and method for improving the stability of the PSCs,and also gave the experimental and theoretical basis for the manufacture and application of waterborne fluoropolymer.However,the working stability of PSCs was far distant in industrial application,the poor stability was one of the main bottleneck of restricting further development of PSCs.The physical mechanism and the effective solution strategy of the weak PSCs stability still remained to be further in-depth study.