Application Research Of Fluorine-containing Additives In Mesoscopic Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells（PSCs）are one of the most promising materials to replace silicon-based photovoltaic devices,the power conversion efficiency（PCE）of PSCs increased from 3.8%to 25.7%.The characteristics of perovskite materials,such as adjustable band gap,high absorption coefficient,low density of defect states,high carrier mobility and large carrier diffusion radius,will contribute to the industrialization of PSCs.Although organic-inorganic perovskite materials have outstanding application ad-vantages,they have some limitations due to their inherent properties.First,they are highly sensitive to water and heat,which can easily lead to material decomposition and device fail-ure.Secondly,the crystallization process may produce many defects.Third,highly efficient PSCs are usually prepared under dry nitrogen conditions,such as nitrogen-filled glove boxes,which complicates the preparation process,increases costs,and is not conducive to commer-cial applications.To simplify the device manufacturing process and promote the commercial application of PSCs,Hongwei Han et al have developed printable mesoscopic perovskite solar cells（MPSCs）that can be prepared using screen printing technology,MPSCs not only have low cost and can be processed in large area,but also have good stability under environ-mental conditions or illumination conditions.Up to now,additive engineering has been proven to improve perovskite mesoporous filling and perovskite film quality by adjusting crystallization behavior and passivation defects,thus improving device performance,this is one of the most effective methods to improve the performance and stability of MPSCs.In order to solve these problems,this paper focuses on the modification of perovskite active layer.To improve the photovoltaic performance and stability of mesoscopic perovskite solar cells,fluorinated compounds were introduced as additives.The research of this paper mainly includes the following two aspects:（1）The preparation of highly effective and stable MPSCs using fluorinated compound Potassium hexafluorophosphate（KPF₆）as additive.The introduction of KPF₆ improved the filling of perovskite in mesoporous media,enhanced the crystallization of perovskite,de-creased the density of defect states in perovskite films,and improved the hydrophobicity of MPSCs.After introducing KPF₆ into MPSCs,the optimal device PCE was 15.39%,which was significantly higher than that of the control device（14.15%）by about 10%.After 50days of storage in air（25±5℃@50±5%RH）,unpacked MPSCs with KPF₆maintained 95%of their initial PCE,while MPSCs without KPF₆ maintained only 80%of their initial PCE.This work provides an effective passivation strategy to improve the PCE and stability of MPSCs.（2）Tetrabutylammonium tetrafluoroborate（TBABF₄）was used as an additive to pre-pare highly efficient and stable MPSCs.TBABF₄ can passivate positively charged halide vacancies by BF₄^-through electrostatic interaction and passivate negatively charged MA va-cancies by TBA⁺,TBABF₄effectively passivates the defects in perovskite films.At the same time,the long alkyl chain and fluorine atom in TBABF₄ have strong hydrophobicity,so the hydrophobicity of perovskite film is enhanced,and its stability is improved.In addition,TBABF₄ enhances the built-in electric field of MPSCs,which facilitates the electron-hole pair dissociation and carrier transport.The PCE of MPSCs was significantly increased from13.88%to 15.78%by elevating the open circuit voltage(V_OC)and fill factor（FF）.Unencap-sulated devices with TBABF₄ addition showed better stability than control devices,with PCE retaining 95%of its initial PCE after 60 days of storage in（25±5°C@50±5%RH）environment,the PCE of the control device only retaining 75%of the initial PCE.