Inorganic Ions Link 2D Layers To Fabricate Efficient And Stable Quasi-2D And 3D/2D Perovskite Solar Cells

Perovskite solar cells(PSCs)are twinkling star in the field of photovoltaics,the power conversion efficiency(PCE)increased from 3.8%to 25.2%repaidly,with the advantages of high absorption coefficient,strong photoluminescence,low electron-hole composite rate and long carrier diffusion length,etc.However,the three-dimensional(3D)PSCs is unstable in the environment of ultraviolet radiation,humidity and high temperature,which restricts its application in commercial.Of these,moisture damages the perovskites crystal structure severely,and the PSCs react with water to produce irreversible decomposition.Two-dimensional(2D)perovskite has long-term environment stability than 3D perovskite,because the bulky organic cations in 2D perovskite can effectively suppress water intrusion.In most cases,2D perovskite is usually not a good choice as a absorption layer for PSCs,due to the large optical band gap and limited charge transport.At the same time,3D perovskite materials have a relatively high density of bulk defects and form trap states at the interfaces with electron transport layers(ETLs)and hole transport layers(HTLs).Therefore,2D perovskite is often used to modify the surface of 3D perovskite to reduce the influence of interface defects,increase the crystallinity of the 3D perovskite film,and improve the surface properties of the film.In this paper,a novel 2D and quasi-2D perovskites are synthesized by adjusting the ionic radius,and this 2D perovskite is further used to passivate the 3D perovskite to improve the PCE and stability of solar cell devices.The research results are as follows:(1)Compared with 3D perovskite,the radius size of the cation in 2D perovskite is not limited by the Goldschmidts tolerance factor(TF),so chemical engineering can be used to adjust the structure of 2D perovskite.The ionic radius controls whether the perovskite lattice can accommodate foreign cations.In this paper,combined with the tolerance factor theory of perovskite and the experimental analysis of defect passivation,we designed to use the monovalent cation SrBr+composed of inorganic alkaline earth metal element(Sr)and halogen(Br)as the spacer cation of 2D perovskite to prepare(SrBr)₂PbI₄ film.X-ray diffractometer(XRD)test results show that the film has a characteristic peak of two-dimensional structure at a small angle(6.4°),the corresponding layer spacing is 13.78(?),and the optical band gap is 2.88 e V.In the experiment,the annealing temperature of the film forming process was further adjusted to precisely control the growth of the(SrBr)2PbI4film.When the annealing temperature was 110°C,the crystallinity of the(SrBr)2PbI4 film was the highest.(2)In the experiment,according to the 2D perovskite general formula(A')₂(A)_n-1B_nX_3n+1,the stoichiometric ratio of the solvent of the precursor solution was adjusted,and the strontium bromide(SrBr₂)and strontium iodide(SrI₂),iodoformamidine(FAI)and lead iodide(PbI₂)are mixed in the precursor solution.The quasi-2D perovskite thin film and solar cell devices with n=20,40,60 were respectively prepared.Among them,the highest efficiency of the cell device with n=60 was 18.46%,and it still maintained 95%of the initial efficiency after 1000 h.The carrier lifetime analysis of quasi-2D perovskites with different layers by time luminescence spectroscopy(TRPL)shows that the non-radiative recombination of carriers in this structure is reduced and the carrier lifetime is improved.(3)Further,(SrBr)⁺were used to passivate the surface of 3D perovskite to obtain a 3D/2D hybrid perovskite solar cell under ambient atmosphere.The corresponding solar cells with FAPbI₃/(SrBr)₂PbI₄ 3D/2D structure achieved a PCE of 22.14%and over 90%retention of the original PCE at 1000 h under air humidity(55%)..In short,this work provides an example of inorganic complex cations that can form 2D perovskites and achieve perovskite solar cells with high PCE and stabilization at the same time.Alkaline earth metals can be synthesized into two-dimensional perovskite,which improves the efficiency of the PSCs,prolongs the service life,and promotes the industrialized development of the perovskite solar cell.