Quality Control On FA_0.75MA_0.25SnI₃ Thin Films And Exploration Of Highly Efficient And Stable Solar Cells

As the most promising environment-friendly photovoltaic material of the next generation,organic-inorganic tin halide perovskites have suitable optical bandgap（1.2-1.4 e V）,high optical absorption coefficient,low exciton binding energy and advantages of extremely high carrier mobility.Therefore,this kind of material stands out from many non-toxic and environmentally friendly non lead perovskite materials and has attracted the attention of photovoltaic researchers around the world.With the joint efforts of scientific researchers at home and abroad,the highest photoelectric conversion efficiency of organic-inorganic tin halide perovskite solar cells has been increased to14.7%.Compared with the beginning of the research,although its performance has been significantly improved,there is still a certain distance from the requirements for commercial production applications.In addition,since Sn-based perovskite is easily degraded by water and oxygen erosion,research on improving the stability of Sn-based perovskite solar cells has gradually become the top priority of research in this field.In order to improve the photoelectric conversion efficiency and stability of Sn-based perovskite solar cells,this paper studies the rational preparation of precursor colloidal solution,the selection of passivation materials,and the passivation and post-treatment of Sn-based perovskite thin films.This paper has carried out four parts of the research in turn:1.Controlling colloidal nucleation size to fabricate high-performance FA_0.75MA_0.25Sn I₃perovskite solar cellsThe research work was carried out on the high-performance dicationic tin-based perovskite FA_0.75MA_0.25Sn I₃,and it was found that the precursor solution had a"colloid nucleation"phenomenon,and the size of the colloid changed with the stirring time.Based on this,we developed a method to control the colloidal core size by controlling the precursor stirring time.By simply adjusting the stirring time of the precursor colloid solution to control the colloidal size inside the precursor to less than 10 nm,it is helpful to obtain continuous,smooth and dense perovskite films with high crystallinity and low defect concentration.The best photoelectric conversion efficiency of 8.11%was obtained in the planar inverted solar cell using this thin film as the light-absorbing layer.This work provides a new perspective for the preparation of high-quality tin-based perovskite films.Based on this,the passivation process will be used as a basis to further improve the quality of perovskite films and device performance.2.Preparation of Efficient FA_0.75MA_0.25Sn I₃ Solar Cells Using Chloride Passivation Materials Containing–OH and–NH₃⁺Based on the problem of defects in the FA_0.75MA_0.25Sn I₃ film,we introduced the passivation material 2,5-diaminohydroquinone dihydrochloride（C₆H₈N₂O₂·2HCl）with–OH groups and–NH₃⁺groups into the FA_0.75MA_0.25Sn I₃ precursor colloidal solution.The FA FA_0.75MA_0.25Sn I₃ perovskite solar cell with a large grain size and higher photoelectric conversion efficiency was constructed through the synergistic effect of passivation groups and Cl^-.Here,we demonstrate that–OH and–NH₃⁺groups can passivate the defects of perovskite through the hydrogen bonding of OH···I and NH…I.And Cl^-can affect the crystallization process so that the film can produce large-sized grains that are more favorable for solar cell during the growth process.The research results show that the use of C₆H₈N₂O₂·2HCl effectively improves the morphology of perovskite films,promotes light absorption,increases film crystallinity,reduces defect state density,reduces unnecessary non-radiative recombination,and also inhibits oxidation of Sn²⁺.The application of the C₆H₈N₂O₂·2HCl-doped FA_0.75MA_0.25Sn I₃ composite film to the inverted planar PSC achieved a champion PCE of9.17%,showing an enhancement factor of 13.1%compared to the control device without C₆H₈N₂O₂·2HCl.In addition,with the improvement of film quality,the storage stability of perovskite films and devices has also been improved to a certain extent.3.Preparation of ordered crystalline FA_0.75MA_0.25Sn I₃ solar cells using passivation materials containing F hydrophobic groupsThe F group has good hydrophobicity and surface segregation properties,and is suitable for the preparation of perovskite films to guide ordered crystallization and improve film stability.In this chapter,we used a material 2-amino-4-fluorophenol（C₆H₆FNO）with F group to reduce the surface energy of the solution-air surface to further precisely control the crystallization process（making crystals from the solution-air surface start orderly growth）,and anchor it on the surface of the perovskite film to enhance the resistance of the film to water intrusion.By this method,we have prepared highly oriented high quality perovskite thin films with longer charge carrier lifetime.The tin-based perovskite solar cell prepared with the film has a high efficiency of 9.75%.In addition,due to the hydrophobic effect of the F group,the resistance to water and oxygen erosion of the film was well improved.As a result,the PSC with C₆H₆FNO-treated perovskite acquires outstanding long-term stability of over 800 hours to retain 80%of its initial efficiency in N₂ environment.To clarify the role of F groups,we also introduced another material,2-aminophenol（C₆H₇NO,which has a similar structure to C₆H₆FNO,but does not contain F groups）into the perovskite precursor colloidal solution as a control group.The solar cells doped with C₆H₇NO also obtained better performance than the original control cells,it was verified that the structures containing–OH and–NH₃⁺functional groups in the previous work generally have passivation effects.Although the solar cells doped with C₆H₇NO also obtained better performance than the original control cells,their efficiency and stability were inferior to those of the devices doped with C₆H₆FNO.The work in this chapter provides a new idea for the controlled growth of FA_0.75MA_0.25Sn I₃ perovskite surface:choose the passivation material with F group,and use its unique characteristics to finally design and manufacture orderly,efficient and stable Sn based perovskite solar cells.4.Preparation of Efficient and Stable FA_0.75MA_0.25Sn I₃ Perovskite Solar Cells Using Multi-F Hydrophobic Group Passivation MaterialsBased on the beneficial effect of the F functional group in the previous work,in this part,we introduce 3,4,5-trifluorophenol（C₆H₃F₃O）containing multiple F groups as an additive material,which is doped into the FA_0.75MA_0.25Sn I₃ precursor.At the same time,an appropriate amount of C₆H₃F₃O was doped into the anti-solvent chlorobenzene to double-treat the film,which further improved the stability of the FA_0.75MA_0.25Sn I₃ film and the battery while ensuring high efficiency.The presence of multiple fluorine groups in C₆H₃F₃O can both enhance the ability of the additive material to segregate to the gas-liquid surface,while the hydrogen bond（OH···I）formed between–OH and Sn I₆^4-can serve as a nucleation site to a greater extent Guiding ordered nucleation of FA_0.75MA_0.25Sn I₃ films from the solution-air surface.On this basis,the film quality has been significantly improved.In addition,C₆H₃F₃O,as an additive material,was simultaneously introduced in the perovskite precursor colloidal solution and the anti-solvent chlorobenzene.Under the premise of not affecting the film quality,the perovskite film was treated with chlorobenzene added with C₆H₃F₃O to maximize the water erosion resistance of the FA_0.75MA_0.25Sn I₃ perovskite film.The existence of multiple fluorine groups anchored outwards can better improve the hydrophobicity of the perovskite film,thereby further improving the stability of the film and solar cells.While ensuring the best photoelectric conversion efficiency of the device up to 10.47%,the solar cell with excellent performance can still maintain 80%of its initial efficiency after 1000 hours of continuous decay test,showing excellent stability.In summary,it is found that high-quality FA_0.75MA_0.25Sn I₃ perovskite films can be prepared by reasonably controlling the colloidal size inside the FA_0.75MA_0.25Sn I₃ perovskite precursor.Based on such thin films,Sn-based perovskite solar cells with excellent performance and good repeatability can be fabricated.Then,by using additive materials with passivation function and hydrophobic function,and using the synergistic passivation of its functional groups,the defects inside the perovskite film can be passivated,and the film stability can be improved,so that the film quality and the performance based on this can be improved.The photoelectric conversion efficiency of perovskite solar cells has been further improved,laying a solid foundation for its commercial application.Based on these studies,tin-based perovskite solar cells are expected to go out of the laboratory as soon as possible and achieve real commercial production applications.