Preparation Of CuFeS₂ Nanocrystals And Its Application In Perovskite Solar Cells

Organic-inorganic hybrid perovskite materials have attracted extensive attention due to their advantages such as high absorption coefficient,low exciton binding energy and long carrier diffusion length.At present,the conversion efficiency of perovskite solar cells has increased from 3.8%to 25.7%,which is comparable to that of crystalline silicon solar cells.However,due to the low formation energy of perovskite materials,environmental conditions such as light,water and heat will degrade perovskite materials,leading to device performance attenuation.In addition,the stability of perovskite solar cells is also closely related to the charge transport layer.The main functions of the hole transport layer are to transfer holes,block electrons,prevent the back electrode from contacting perovskite directly,and reduce the influence of external factors such as humidity and oxygen on perovskite.At present,most high-efficiency perovskite solar cells use organic materials as the hole transport layer,but the organic hole materials have low conductivity,and must be used with additives,such as lithium salt or cobalt salt.These additives have hygroscopic properties,which affect the stability of devices.Therefore,the use of inorganic hole transport materials instead of organic hole transport materials is an effective way to improve the stability of perovskite batteries,because inorganic hole materials have good chemical stability.In addition,interface engineering is also an important way to improve the conversion efficiency and stability of perovskite solar cells.Surface modification can passivate surface defects of perovskite absorption layer,reduce photogenerated carrier recombination,improve battery conversion efficiency and enhance battery stability.In this paper,CuFeS₂ nanocrystals were synthesized by hot injection method,and CuFeS₂ nanocrystals were used as hole transfer materials to prepare perovskite solar cells,which can improve the stability of the cells.The CuFeS₂ nanocrystals were deposited on the surface of perovskite as modification layer,the surface defects of perovskite were passivated,the recombination probability of carrier was reduced,and the efficiency and stability of perovskite cells were improved.Specific research contents are as follows:（1）CuFeS₂ nanocrystals were prepared by hot injection method.XRD,UV-vis absorption spectrum,TEM and other characterization methods were used to demonstrate that the synthesized CuFeS₂ nanocrystals have chalcopyrite structure,and the nanocrystals have appropriate grain size and good dispersion.The energy band structure of CuFeS₂ was determined by UPS.The results show that the valence band of CuFeS₂ matches that of perovskite and can be used as hole transport material.The results of PL and TRPL show that CuFeS₂ can effectively extract and transport photogenic holes generated by perovskite.CuFeS₂ was used as hole transfer material to prepare perovskite solar cells,and the optimal efficiency of 14.6%was obtained.In addition,the CuFeS₂ nanocrystalline cell has higher stability than the cell based on organic hole material Spiro-OMe TAD.The results show that CuFeS₂ can be used as hole transport material to prepare efficient and stable perovskite solar cells.（2）CuFeS₂ nanocrystals were used as surface modification materials to modify the perovskite absorption layer.PL,TRPL,space charge-limited current（SCLC）,electrochemical impedance spectroscopy and other experimental results show that CuFeS₂ nanocrystals can passivate surface defects of perovskite and reduce photogenic charge recombination.The energy band structure of each layer of materials shows that the valence bands of perovskite,CuFeS₂ and hole transport materials form a stepped arrangement,which is more conducive to the separation and transport of holes.XPS test results show that there is strong interaction between CuFeS₂ nanocrystals and perovskite films.By optimizing the experimental conditions,the conversion efficiency of perovskite solar cells based on CuFeS₂ modification is increased to 20.17%,while that of perovskite cells without modification layer is 18.64%.Moreover,the addition of CuFeS₂ modification layer enhances the stability of perovskite solar cells.The results show that CuFeS₂ nanocrystals can be used as modification layer to improve the conversion efficiency and stability of perovskite cells.