Study On Interface Optimization Of Perovskite Solar Cells

With the rapid development of economy and society,the demand for energy is increasing day by day.Solarenergy,an inexhaustible clean energy,has aroused people’s wide attention.Attributed to the simple fabrication method,low manufacture cost and high power conversion efficiency（PCE）,perovskite solar cells（PSCs）have become a rising star of the third generation of solar cells,but PSCs still have the problems such as the poor stability and high interface recombination.In this paper,our work focus on decreasing the trap density,suppressing the carrier recombination and optimizing the interface between perovskite and hole-transporting layer.We improve the performance of PSCs by replacing acetonitrile（ACN）in Spiro-OMeTAD solution and passivating surface defects under the action of cyclohexane methylamine（CMA）and cyclohexane methylamine iodide（CMAI）.The main research contents and results are as follows:（1）The most common hole-transporting material is spiro-OMeTAD,which requires bis（trifluoromethane）sulfonimide lithium salt（LiTFSI）and4-tert-butylpyridine（TBP）as additives to fix its poor conductivity and hole mobility instead of applying to PSCs directly.ACN,the solvent of LiTFSI,is known as a polar solvent and it can cause the corrosion of perovskite layer,thus the use of ACN challenges the efficiency and stability of PSC.In attempt to abate the degradation of perovskite,a series of alcohols with smaller polarity were introduced as an alternative to dissolve LiTFSI.When we replaced ACN with isopropanol（IPA）,the quality of the perovskite film was higher,the carrier recombination and trap density were reduced,and a PCE of 19.43%was finally obtained.（2）We applied cyclohexane methylamine（CMA）solution on the perovskite film and found that CMA would react with excess lead iodide（PbI₂）.The remaining PbI₂was distributed at the grain boundary of perovskite,which passivated the defects on the surface of perovskite,reduced the trap density of the film,and inhibited carrier recombination.Compared with blank device,the passivated device showed an enhanced open-circuit voltage(V_OC)and thus a higher efficiency of 20.30%.In addition,the passivated device showedgreatly improved long-term stability,maintaining 87.27%of its initial efficiency after 45 days exposure in air（30±5%RH%,25℃）.（3）The cyclohexane methylamine iodide（CMAI）solution was spin-coated on 3D perovskite layer,resulting in an in situ formation of 2D perovskite CMA₂PbI₄ layer by the following reaction of CMAI with surplus PbI₂.2D perovskite could be uniformly coated on 3D perovskite to form 2D/3D perovskite stacking layer.On the one hand,the 2D capping layer acted as a passivation layer that can effectively reducing the trap density at the 3D perovskite surface and suppressed the carrier recombination.Compared with 3D device,the PCE of 2D/3D device increased from18.76%to 21.05%,with a decreased hysteresis effect.On the other hand,owing to the superior hydrophobicity of 2D perovskite film,the 2D/3D device showed aimmenselyenhanced durability,maintaining 80.77%of its original efficiency after 52days exposure in air（30±5%RH%,25℃）.