Synthesis, Characterization Of Lead Iodide-based Layered Perovskite Organic-inorganic Hybrids Materials

Layered perovskite-type organic-inorganic hybrids can integrate usefulcharacteristics organic and inorganic compounds by self-assembly on a molecularlevel. Layered perovskite-type organic-inorganic hybrids have novel optical andelectrical properties. Owing to the two-dimensional quantum confinement effects, theexciton binding energy is substantially enhanced as large as a few hundreds meV,which makes strong photoluminescence and electroluminescence occur even at roomtemperature and make it is possible for using in optical devices. However, theessential relationship between structures and properties is not clear, especially thebilayed hybrids are difficult to synthesis so that there are only a few papers. So thisarticle researched on the synthesis of monolayered and bilayered hybrids to explorethe law of ingredient–structure–energy band-properties.This dissertation focuses on the synthesis and the structures of the hybrids withchemical formula [CnH2n+1NH3]2(CH3NH3)m-1PbnI3m+1(n=5-12， m=1,2) in theory,which is expected to have pure monolayered and bilayered perovskite-type structurehybrids. Research on synthesis process systematically and summary the continuousincrease of carbon atoms how to affect the structures and performance of hybrids.When monolayered hybrids were synthesized via solution method, the kinds ofsolvents did not affect the products structure. When the bilayered hybrids in theorywere synthesized, the best products are under alcohol and HI solvents heated at90℃for2hours. The ratio could affect crystallization of products, more thanstoichiometric ratio of PbI2and alkylamine salts is not good for bilayered hybrids, butadd more methylamine to ingredients can prevent composing monolayered hybridsand get bilayered hybrids effectively.The results demonstrate that the XRD of the product powder have a high degreeof preferred orientation along(002l)direction，all hybrids feature layered structures,which is agree with SEM. The calculated interlayer distance differences between thebilayered and the monolayered hybrids are almost the height of a [Pbl6]2-octahedron.The number of carbon atoms of straight-chain alkanes amine has linear relation withinterlayer distance, the increase of interlayer distance with adding a carbon inmonolayered and bilayered, which means that increasing organic layers can’t bringmore distortion of inorganic octahedron. The TG-DSC curves show that the organic part will first decompose for hybrid with heating. As the growth of the carbon chain,hybrids thermal stability will enhance, except the long carbon chain (n>10) hybridswhich have different conformations; Adding more layers of hybrids will decreasethermal stability. From the UV-vis spectrum of the products indicate that the numberof layers of the inorganic perovskite layer has a greater impact to the bandgap than theincrease of arbon atoms，the bandgap of bilayered structure is significantly less thanthe band gap of monolayered structure．From PL emission spectra we can see thereare two exciton emissions at522nm and550nm of monolayered hybrids, but there arethree exciton emissions of bilayered hybrids A very obvious red shift we findd inbilayered hybrids and the intensity of the two typical peaks which at longerwavelength is much lower than monolayered hybrids. What’s more, the changing oforganic alkyl amines has greater influence on the luminescence of bilayered hybridsthan monolayered hybrids.