Structure And Properties Of (RNH₃)₂PbX₄ Series Organic-inorganic Perovskite-type Materials

Organic-inorganic assembly layered perovskite-type materials integrate useful organic and inorganic characteristics on a molecular level. Organic molecules provide structural diversity, plastic mechanical properties, large polarizability, ease of processing and high fluorescence efficiency, whilst inorganic materials offer the potential for a wide range of electronic properties, magnetic and dielectric transitions, substantial mechanical hardness, and thermal stability. Special properties and functions would be got if the hybrid materials could combine desirable physical properties characteristic of both components within a single composite. It provides us an good opportunity to study its structure and properties. The inorganic components mainly reported in this study are lead halides (PbX₂). The various organic components were used to modulate the dimension of the hybrid structure. On the base of variety dimension, the effect of the change of the halogen on structure and properties has been studied in this paper. The deposition of films is also taken into the consideration to study the effect of the conditions on the structure and properties of the films.(C₆H₅C₂H₄NH₃)₂PbX₄ crystals had been prepared via layered solution method. XRD and SEM of powder crystals showed the synthesized samples are featured with layered crystal structure. The structure rietvle was conducted by X'Pert High Score program. FTIR shows that the absorption peaks of N-H shift to lower wavenumbers with change of halogen. Raman spectrums also show that vibration frequency of Pb-X bond reduces duo to the increase of the radii of halogen. Thermal analysis shows that the interaction of H bond has been enhanced. With regard to CH_sNH₃PbX₃, the three axes gradually expanded with the replacement of halogen.(RNH₃)₂PbI₄ thin films were prepared by spin-coating method to study the effect of thermal annealing and substrate temperature as well as the concentration of the solution on the quality and structure. Highly oriented films were obtained via this method and the mentioned conditions were all optimized. The series films of (C₆H₅C₂H₄NH₃₎2PbCl_xBr_4-x and (C₆H₅C₂H₄NH₃)₂PbBr_xI_4-x were deposited by spin-coating. XRD patterns show that the peaks along (002l) direction shift to higher position with the decline of variable x. Strong exciton absorption bands were observed in the UV-Vis spectrum. These absorption bands had been attributed to the excitons formed in the inorganic layers by the transition from Pb²⁺ (6s) to Pb²⁺ (6p) orbital. The exciton absorption peaks and emission peaks shifted to higher energy with the replacement of halogen, which indicated that the change of halogen could tune the energy band structure.