Study On The Structural Phase Transition And Photoelectric Properties Of Two-dimensional Organic-inorganic Hybrid Perovskite

Organic-inorganic hybrid perovskite materials with unique properties and structural diversity.Not only the structure combines the characteristics of organic and inorganic parts,but also has the advantages of organic parts and inorganic parts in physical properties.So that it has the characteristics of high thermal stability,strong plasticity,semiconductivity and optical performance etc.Therefore,it has received extensive attention and has a very broad application prospect.In recent years,organic-inorganic hybrid perovskite phase change materials have been continuously developed.Among them,the hybrid perovskite with ferroelectric phase transition has attracted great interest from researchers.In addition,with the advent of the high-performance organic-inorganic hybrid perovskite photovoltaic device,it shows great potential in the field of optoelectronic devices,and has made breakthroughs in a series of optoelectronic devices.In this paper,seven organo-inorganic hybrid perovskites were synthesized with 1,6-hexamethylenediamine,cyclohexylmethanamine,2-chloroethylamine,2-iodiethylamine and dimethylamine.The main research contents of this paper are as follows:（1）The compound(H₃NC₆H₁₂NH₃)（CH₃NH₃）Pb₂Br₇（1）was synthesized with 1,6-hexamethylenediamine.We conduct a dielectric test on compound 1,the results show that the dielectric constant began to show obvious abnormality when the temperature rose to around 325 K,and the ladder-shaped dielectric anomaly is clearly observed,which indicated that its structure changed during the process of temperature change.In addition,differential scanning calorimetry（DSC）test results confirmed that compound 1 underwent structural transformation in the process of temperature rise and drop.We further confirmed that the order-disorder transformation of organic cations was the main reason for the induction of phase transition through single crystal structure analysis.In addition,using cyclohexylmethanamine and 2-chloroethylamine as the organic element to assemble and synthesize two cases of organic-inorganic hybrid perovskite materials with ferroelectric phase transition:（ClCH₂CH₂NH₃）PbBr₃（2）and(C₆H₁₁CH₂NH₃)₃Bi₂Br₉（3）.The pronounced dielectric anomaly peaks,suggesting the possible ferroelectric activity of compounds 2 and 3,and we also further confirmed the phase change of compounds 2 and3 by DSC（near the temperature of 300 K and 333 K）,respectively.We found that the crystal space group respectively from the C2/c into Cc and Pnma into Pna2₁,belongs to the ferroelectric phase transition space group change through the crystal structure analysis.（2）Four two-dimensional layered perovskite compounds were synthesized with 2-iodiethylamine,dimethylamine and 1,6-hexandiamine:（ICH₂CH₂NH₃）₂PbBr₄（4）,（BrCH₂CH₂CH₂NH₃）₂（CH₃NHCH₃）Pb₂Br₇（5）,（CH₃CH₂CH₂CH₂CH₂NH₃）₂（CH₃NHCH₃）Pb₂I₇（6）,(H₃NC₆H₁₂NH₃)CsPb₂Br₇（7）.The optical band gap,conductivity and photoelectric response of compounds 4,5,6 and 7 were tested.We found that all of them have relatively excellent photoelectric detection performance.We successfully designed the first DJ-type 2D hybrid perovskite 1,which contains both the inorganic alkali metal and organic cations,and applied to the polarized light detection.Its unique polarization response stems from its own structural anisotropy.In addition,the compound 1 shows excellent photoelectric response and stability,and has potential application value in field of photoelectric detection and polarized light detection.