The Influence Of Fluoride Modification On Perovskite Solar Cell Performance

In recent years,organic-inorganic hybrid perovskite film solar cells（PSCs）have been developed rapidly as the most promising photovoltaic technology.However,the poor stability of PSCs has hampered the commercialization process.In this paper,the PSCs structure of FTO/TiO₂dense layer/TiO₂mesoporous layer/MAPbI₃active layer/carbon electrode was prepared in air,improving the photovoltaic performance and long-term stability of PSCs,the main contents are as follows:Firstly,the mesoporous layer of TiO₂was treated with NaF and LiF and LiF+NaF solution,and the effect of alkali metal fluoride modified TiO₂mesoporous layer on the properties of PSCs was studied.It was found that Li⁺,Na⁺and F^-ions were adsorbed on the surface of TiO₂,and the adsorption of H₂O,O₂and N₂on the surface was reduced,the substitution of hydroxyl groups（OH^-）on the surface of TiO₂mesoporous layer by F^-optimizes the crystallization and growth environment of perovskite crystals,and enhances the crystallinity and grain size of perovskite polycrystalline films,the quality of the active layer of MAPbI₃perovskite was improved.The effect of LiF+NaF mixed alkali metal fluoride modified TiO₂mesoporous layer is better than NaF and LiF single alkali metal fluoride,and the best PCE is achieved when the annealing holding time is 20 min after LiF+NaF mixed solution treatment.The PSCs were assembled with the multi-layer film electrode and the carbon electrode.The PSCs were tested under the irradiation of AM1.5 G with the radiation intensity of 100m W/cm².The PCE of the best device was 10.74%.The unencapsulated device was stored in the natural environment and kept 95%of the initial PCE after 92 days,showing long-term stability.Secondly,the effect of NaF modified MAPbI₃perovskite polycrystalline film on perovskite active layer and PSCs properties was studied.It is found that the highly electronegative F atom partially displaces the I atom in the crystal structure of perovskite by adding NaF to the precursor solution of MAPbI₃perovskite,thus forming a stronger chemical bond with cations,enhancing the stability of perovskite crystal structure.At the same time,highly symmetric Na⁺ions enter the lattice to replace asymmetric MA⁺ions,which reduces the lattice distortion of perovskite crystals and optimizes the crystal structure of perovskite to grow large grains along[110]orientation,improving the crystallization quality of perovskite films.It was found that the concentration of NaF was 0.5 mmol/L,the best crystallization effect was obtained by modifying MAPbI₃crystal,and the quality of perovskite films was the best.The multi-layer film electrode was combined with carbon electrode to form PSCs.The PSCs were tested under 100 m Wcm^-2,AM1.5G simulated sunlight irradiation.The optimal device obtained 11.26%PCE.As the NaF modification improves the moisture resistance of the MAPbI₃perovskite polycrystalline film and the hydrophobic carbon electrode prevents water vapor erosion,the PSCs show good long-term stability.The unpackaged PSCs were evaluated for their stability in air aging,and it was found that after 100 days,the device maintained more than 95%of the initial PCE.