Synthesis And Photoelectric Thermal Properties Of Low-Dimensional Diamine Metal Halide Perovskites

Low-dimensional organic-inorganic hybrid metal halide perovskite materials have attracted widespread attention due to their excellent properties.In this paper,a series of low-dimensional lead-free metal halide perovskite materials were synthesized by using diamine as organic component and antimony,bismuth and tin as inorganic components instead of lead.In the first part,1,7-heptanediamine was used as an organic template,and four metal halide perovskites[NH₃（CH₂）₇NH₃]₂[SbBr₆]Br（1）,[NH₃（CH₂）₇NH₃]SbI₅（2）,[NH₃（CH₂）₇NH₃]₂[BiBr₆]Br（3）,[NH₃（CH₂）₇NH₃]BiI₅（4）were synthesized by reaction with antimony halide and bismuth halide,respectively.The obtained samples were tested by Infrared and PXRD to confirm that the sample used for characterization is pure;Differential scanning calorimetry（DSC）test was performed on compounds 1-4,and the results showed that compounds 1-4 had reversible phase transitions,which occurred at about 238 K,315 K,365.5 K,380 K,and 351.7 K,respectively.The second harmonic generation（SHG）test of compound 1 showed that compound 1 had a reversible SHG signal,revealing that the space group of the crystal of compound 1 had undergone a transition from non-centrosymmetry to centrosymmetry near the phase transition point.In addition,cyclic testing over 5 cycles showed that compound 1 had nonlinear optical switching properties.Through crystal structure analysis,it can be seen that compounds 1 and 3 have a zero-dimensional structure,and compounds 2 and 4have a one-dimensional structure.The results of UV-Vis spectroscopic testing of compounds 1-4 showed that the band gap values were 2.54 eV,1.91 eV,2.66 eV,and1.89 eV,respectively.The smaller band gap value of 1.89 eV in Compound 4 is comparable to most hybrid organic-inorganic hybrid lead-halide-type ferroelectric semiconductors.This research work can provide ideas for the future development of low bandgap lead-free perovskite materials.In the second part,N,N′-dimethyl-1,3-propanediamine was used as an organic template,which reacted with antimony halide and tin halide,respectively,to obtain threeantimony-basedmetalhalideperovskitematerials[CH₃NH₂（CH₂）₃NH₂CH₃]SbCl₅（5）,[CH₃NH₂（CH₂）₃NH₂CH₃]SbBr₅（6）,[CH₃NH₂（CH₂）₃NH₂CH₃]SbI₅（7）and two tin-based metal halide perovskite materials[CH₃NH₂（CH₂）₃NH₂CH₃]SnCl₆（8）,[CH₃NH₂（CH₂）₃NH₂CH₃]SnBr₆（9）,infrared and PXRD testing of compounds 5-9 to determine the purity of samples for subsequent characterization;DSC tests on compounds 5-9 showed that compounds 6,8 and 9 had reversible phase transitions at approximately 285.8 K,335.3 K,301 K,and 359 K,respectively,while compounds 5 and 7 did not undergo phase transitions.SHG testing of the compound showed that compound 6 had a reversible SHG signal,revealing that the spatial group of crystals had undergone a transition from non-centrosymmetry to centrosymmetry near the phase transition point.In addition,cyclic tests within 5 cycles showed that compound 6 has nonlinear optical switching characteristics and is a good linear optical switch material.Through crystal structure analysis,it can be seen that three antimony-based materials have a one-dimensional structure,and the other two tin-based materials have a zero-dimensional structure.Moreover,the room temperature single crystal crystallization of compound 6 in the chiral P2₁2₁2₁ space group corresponds to the measurement results of SHG.The results of UV-Vis spectroscopic testing of compound 5-9 showed that the estimated values of the band gap were 2.73eV,2.62 eV,1.98 eV,3.18 eV and 2.69 eV,respectively,showing band gap controllability.In summary,nine kinds of low-dimensional lead-free metal halide perovskite materials were synthesized with antimonium halide,bismuth halide and tin halide,using diamine as organic components,and their properties were tested,which provided ideas for further exploration of low-dimensional metal halide perovskite materials.