Performance Research Of Photovoltaic Devices Based On 2D CsPbI₃ Films

Compared with organic-inorganic hybrid perovskites,inorganic Cs Pb I₃ perovskite shows better thermal stability,and has been widely studied.So far,Cs Pb I₃-based perovskite solar cells（PSCs）has achieved a power conversion efficiency（PCE）of21.0%.However,the too small Cs⁺ionic radius（1.81（?））makes Cs Pb I₃ exhibit phase instability at room temperature.Improving phase stability has become a major challenge and an urgent problem for Cs Pb I₃ PSCs.Recently,two-dimensional（2D）or quasi-2D layered perovskites have been commonly used to stabilize the black-phase Cs Pb I₃.Hydrophobic organic cations in layered perovskites can not only prevent the destruction of crystal lattice from water and oxygen molecules,but also generate steric hindrance effect,thus improving the phase stability.However,insulating interlayer organic cations hinder the effective extraction and transport of charge,which greatly reduces the photovoltaic performance of 2D PSCs.In order to improve the PCE of 2D PSCs,we use solvent engineering and additive engineering to improve the films quality of 2D layered perovskite formed by different cations and the photovoltaic performance of the corresponding devices.The specific work is as follows:1)2D Ruddlesden-Popper（RP）Cs Pb I₃ exhibit enhanced phase stability compared with three-dimensional（3D）Cs Pb I₃.However,the issue of uncontrollable crystallization process makes the film quality poor,and limits its photovoltaic performance.Here,the influence of binary-mixed-solvent on the film quality and photovoltaic properties of（PEA）₂Cs_n-1Pb_nI_3n+1（n=5）based on phenylethylammonium cation（PEA⁺）are studied in detail.It is demonstrated that crystallization rate and crystal growth process can be controlled by adjusting the amount of dimethyl sulfoxide（DMSO）.Adding 10%DMSO in the pure dimethyl formamide（DMF）to optimize the solvent composition can obtain perfect coverage,larger flaky 2D grains,reduced grain boundaries as well as better vertically oriented films relative to the substrate due to the formation of more stable intermediate phase.This can form good interface contact,which is beneficial to charge transport/extraction between Ti O₂（electron transport layer,ETL）and perovskite,and finally improving device performance.Compared with the reference device based on pure DMF,the enhancement of PCE for the optimized device based on DMF:DMSO（9:1 v/v）is 3.57%.This work illustrates the effect of crystallization kinetics on RP Cs Pb I₃ film growth process and provides a simple and effective method for the preparation of high-performance 2D Cs Pb I₃ solar cells.2)2D perovskites stabilized by alternating cations in the interlayer space（ACI）show great potential in PSCs,and have attracted more and more attention.Adjusting the solvent composition of the precursor solution is critical to the photovoltaic performance of 2D RP Cs Pb I₃ PSCs.However,the effect of solvent properties on the morphology/photoelectric properties of ACI perovskite films and the final photovoltaic performance is still poorly understood.Here,we reports an 2D ACI PSCs with chemical formula（GA）Cs_nPb_nI_3n+1（n=5）via solvent engineering,and the PCE reaches 10.49%.Using mixed solvent with DMF:DMSO（6:4 v/v）to prepare（GA）Cs_nPb_nI_3n+1（n=5）films can eliminate phase segregation,improve morphology,reduce defect density and enhance carrier mobility,thus improving device performance.This work first reports2D ACI PSCs based on Cs Pb I₃,and provides preliminary guideline for achieving higher-performance 2D PSCs in the future.3)The additives have an important effect on the photovoltaic performance of2D/3D PSCs,methylammonium chloride（MACl）is one of the commonly used additives to improve the photovoltaic performance.Here,we introduces MACl additive into the precursor solution to prepare the（1-NA）₂Cs₄Pb₅I₁₆ perovskite film based on 1-naphthylamine（1-NA）.when the concentration of MACl is 1%,the film quality can be improved.It is found that such improvement is further demonstrated by the photoelectric properties,including suppressed non-radiative recombination and enhanced carrier mobility.Consequently,we finally realize a high-performance 2D RP PSCs,the PCE reaches 12.92%.