Study On Synthesis And Photoelectric Devices Of Quasi-two-dimensional Lead-free Perovskites

Organic-inorganic halide perovskites have attracted increasing interest because of their advantages such as simple fabrication process,low cost,premium optoelectronic properties and so on.Among these perovskites,quasi-2D layered organic-inorganic perovskites showed the tunable bandgap,larger exciton binding energy and high carrier mobility characteristics,and could be potentially used in different optoelectronic devices.However,quasi-2D perovskites still face some typical challenges to fulfill their commercial applications.Especially for the high toxicity of the traditional lead-based hybrid perovskites materials,it needs to be solved urgently.In this respect,exploring the environmentally friendly and efficient quasi-2D perovskites will promote their commercial applications.In this paper,the quasi-2D perovskites（PEA）₂（MA）_n-1Sn_n I_3n+1（n=1,2,3,5,∞）have been synthesized based on phenylethylamine（PEA）and methylamine（MA）organic components with tin（II）iodide（SnI₂）inorganic component.Changing the number of inorganic layers in these perovskites will result in the various crystal structures and optoelectronic properties.Moreover,we fabricated the light-emitting diodes and photodetectors base on these perovskites and study the devices’performances.The main research are listed as follows:1.IodophenethylamineandIodmethylaminearesynthesizedwithβ-phenylphenethylamine,methylamine and hydroiodic acid respectively.The quasi-2D（PEA）₂（MA）_n-1Sn_nI_3n+1（n=1,2,3,5,∞）with different inorganic layer numbers are synthesized by solution cooling method.The structure and morphology of the perovskites are tested by a series of test instruments.The valence bands of perovskites are measured by ultraviolet photoelectron spectroscopy（UPS）.2.The synthesized quasi-2D perovskites are dissolved in N,N-dimethylformamide（DMF）solution.Then the perovskites films are prepared by spin-coating method and tested by scanning electron microscopy（SEM）,ultraviolet-visible absorption spectroscopy（UV-Vis）,and transient photoluminescence spectroscopy（TR-PL）.Through tests and analysis,it can be found that with the increase number of the inorganic layers,perovskites films present the red-shift absorption peaks and photoluminescence peaks with decreased band gaps and shortened carrier transient lifetime.Based on these perovskites films,we have fabricated the redlight-emittingdiodeswiththestructureof ITO/PEDOT:PSS/PVK:NPB/Perovskite/TPBi/LiF/Al.TheLEDsexhibitthe electroluminescence（EL）peaks at 624 nm（n=1）,712 nm（n=2）and 780 nm（n=3）,respectively.The optimal device（n=1）presents a turn-on voltage of 3 V,a maximum luminance of 6.64 cd/m² and a maximum current efficiency of 0.019 cd/A.Moreover,the devices’performances have been analyzed based on the AC impedance measurements.3.Based on（PEA）₂（MA）_n-1Sn_nI_3n+1（n=1,2,3）perovskites films,we have fabricated the photodetectors with the structure of ITO/PEDOT:PSS/Perovskite/PCBM/Ag.Firstly,the surface photovoltage spectrum tests are performed,and then the devices are tested for performances based on UV-Vis selected excitation light at a specific wavelength.The optimal device（n=3）shows a light response rate of 1.36×10⁴ mA/W,a light detection rate of5.44×10¹33 cmHz^1/2/W and a light on-off ratio is 1.39×10⁴ under the bias of 0 V and 682 nm（0.2 mW/cm²）illumination.Meanwhile,the rise time and fall time of the device’s light response are 8 ms and 7 ms,respectively.