Study On The Post-modification Of Two-dimensional Organic-inorganic Hybrid Perovskite

Hybrid organic-inorganic perovskites（HOIPs）materials have shown many promising photoelectric properties,including high absorption coefficient,low exciton binding energy and appropriate band gap.At present,the highest photoelectric conversion efficiency（PCE）of three-dimensional（3D）organic-inorganic hybrid perovskite materials has exceeded 25%.However,the poor environmental stability hinders its further development.Two-dimensional（2D）organic-inorganic hybrid perovskite materials have been favored by many researchers due to their advantages of abundant choices of organic cations.Most importantly,the introduction of hydrophobic cations can effectively improve the environmental stability of 2D HOIPs.Herein,two 2D perovskites were prepared by solution method and hydrothermal method,respectively,that is HDAPb I₄（HDA=1,6-hexanediamine）and EDAMn Cl₄（EDA=1,2-ethylenediamine）.Then,their structures and properties were post-modified through the organic and inorganic components,respectively.The amidation reaction（between-NH₃⁺and acyl chloride）and the polymerization reaction（between-NH₃⁺and epoxy groups）were introduced into 2D HOIPs.Four HDAPb I₄-polymer films were fabricated.At the same time,considering the toxicity and environmental instability of 2D lead halide perovskites,Mn²⁺together with Cd²⁺was used instead of Pb²⁺.As a result,a series of X%Cd²⁺@EDAMn Cl₄（X=30.79、45.94、69.91、81.63 and 87.36）perovskites were synthesized.The compounds involved in this paper are listed as follows:HDAPb I₄[NH₃（CH₂）₆NH₃]Pb I₄（MC-HDA）Pb I₄ MC-[NH₃（CH₂）₆NH₃]Pb I₄（SC-HDA）Pb I₄ SC-[NH₃（CH₂）₆NH₃]Pb I₄（R-PO-HDA）Pb I₄ R-PO-[NH₃（CH₂）₆NH₃]Pb I₄（S-PO-HDA）Pb I₄ S-PO-[NH₃（CH₂）₆NH₃]Pb I₄EDAMn Cl₄[NH₃（CH₂）₂NH₃]Mn Cl₄XCd²⁺@EDAMn Cl₄ Cd²⁺@[NH₃（CH₂）₂NH₃]Mn Cl₄（X=30.79%、45.94%、69.91%、81.63%和87.36%）HDA=1,6-hexanediamine;MC=malonyl chloride;SC=succinyl chloride;R-PO=R-（+）-propylene oxide;S-PO=S-（-）-propylene oxide;EDA=1.2-ethylenediamine;DMSO=dimethylsulfoxide;DMF=N,N-dimethylformamide;PDMS=polydimethylsiloxane.1.（MC-HDA）Pb I₄ and（SC-HDA）Pb I₄ perovskite-polymer films were first prepared with HDAPb I₄ perovskite as the matrix.As a result,the interlayer spacing of[Pb I₄]_n^2n-was extended and the optical properties was modified.The perovskite-polymer film with a more uniform morphology exhibited a good photoelectric response,so that it could be applied in photoelectric detectors.2.Stability is one of the major issues for hybrid organic-inorganic halide perovskites.In the organic aspect,increased hydrophobicity can be beneficial to the enhanced stability.Different from the previous R-group hydrophobic modification in organic R-NH₃⁺cation,herein,NH₃⁺modification using epoxide is reported to improve the stability of hybrid halide perovskite.We integrate the chiral propylene oxide（PO）into HDAPb I₄ through the grafting of PO onto HDA.The-NH₃⁺hydrophobic modification is much favorable for stability improvement.As a result,the resultant（R/S-PO-HDA）Pb I₄thin film is stable in water for more than one hour,while the untreated HDAPb I₄ thin film decomposes immediately.Moreover,（R/S-PO-HDA）Pb I₄ could keep the photoelectricity of HDAPb I₄ and the chirality of PO.This work would inspire the further study on the perovskite-based epoxide polymer.3.Considering the toxicity of 2D lead halide perovskite and the usage of non-green organic solvents（DMF,DMSO and etc.）,we synthesized water-soluble EDAMn Cl₄perovskites by hydrothermal method.EDAMn Cl₄ was doped with various transition metals(such as Fe²⁺、Co²⁺、Cu²⁺、Zn²⁺、Ag²⁺and Cd²⁺).It was found that only Cd²⁺doped EDAMn Cl₄ was the most stable,,which is confirmed by the theoretical calculation results that the doping energy of Cd²⁺was the smallest.The Cd²⁺@EDAMn Cl₄ has improved photoluminescence and superior stability in water.69.91%Cd²⁺@EDAMn Cl₄ can keep stable in water for 90 min.Firthermore,the composite of69.91%Cd²⁺@EDAMn Cl₄-PDMS（polydimethylsiloxane）is more stable and exhibits good mechanical property.The innovation of this paper lies in the post-modification of 2D HOIPs.The target materials were studied in detail by various characterization methods.The results confirmed that the post-modified 2D HOIPs can generate some novel properties（such as chirality,improved stability and etc.）,while they can maintain the original photoelectricity as a semiconductor.This thesis would provide more inspirations in the research field of HOIPs modification.