Investigation On The Dynamic Tructure Of （p-Cl-C₆H₄-NH₃）₃CdBr₅and P3HT By In-situ FTIR Spectroscopy

In this thesis, using in-situ infrared spectroscopy as the main research technology, we did some researches on two materials, which are very representative of the materials applied to organic-inorganic composite/hybrid semiconductor devices. One is a new organic-inorganic perovskite hybrid crystal (p-Cl-C6H4-NH3)3CdBr5, and the one is regioregualr poly(3-hexylthiophene), abbreviated as rr P3HT. It is well-known that thermal annealing in one of the most common and effective post-process technique used to improve the performances of electronic devices. By using some in-situ infrared accessories, we can simulate thermal annealing process, and collect infrared spectrum in real time, which are very useful to analyse dynamic structureFor the new crystal (p-Cl-C6H4-NH3)3CdBr5, its structure features, thermal stability, thermal decomposition process, and the stability of its chemical bonds were mainly discussed. As for P3HT, which has been well developed and extensively used, the evolution of molecular structure and crystalline states in solid state when it is under thermal annealing were the focuses of our studies, and the most important effects on the P3HT films were explained. Base on the above results, we used the high temperature and high pressure in situ infrared accessories to heat the two materials in a high pressure under a nitrogen atmosphere, and analysed the new features of dynamic structure compared with that manifested under atmospheric pressure. The main results are as follows:(1) The crystal structure of (p-Cl-C6H4-NH3)3CdBr5belongs to the point group P21/c, and its original cell comprises three p-haloro-anilinium ligands and one CdBr53-anion. Compared to the conventional layered organic-inorganic perovskie hybrid structure, the inorganic layer of this crystal is composed of zigzag chains formed by the vertex-sharing CdBr6octahedral along the b-axis, and the organic cations fill in the spaces between anion layers. First, by analyzing the results from thermal analysis, in situ XRD and in situ infrared spectroscopy tests, we found that the thermal decomposition of this crystal origins from the fracture of Cd-Br bonds in the inorganic octahedron. Its thermal decomposition equation is: (p-Cl-C6H4-NH3)3CdBr5â†'p-Cl-C6H4-NH3Br+CdBr2With the calculation and attribution of the infrared spectrum of p-Cl-C6H4NH3, it was found that the three peaks localized at822,818and811cm-1represent the three ammonium cations in the asymmetric monomer. The curves of their intensity variation with temperature reveal that the two bonds Cd-Br2and Cd-Br5are the most instable bonds and they first break in thermal decomposition process. The structure that the angle of Cd-Br2bond and the length of Cd-Br5deviate far from the regular octahedron structure determined the stability of this crystal.(2) From the analyses of in situ diffuse reflectance infrared spectrum of (p-Cl-C6H4-NH3)3CdBr5, we pointed out that the absorption band at～2645cm-1contains vibration information of the crystal lattice. In another word, the crystal structure changes vary with temperature can be reflected clearly by the intensity of this band. So we monitored this band and the group peaks of822,818and811cm-1at atmospheric pressure,2.0MPa and4.0MPa under nitrogen. The results reveal that the process of the crystal structure changes with temperature were slowed down under high pressure.(3) As for P3HT, we discussed dynamic structures of the thiophene main chain and the alkyl side chain during thermal annealing by using in-situ infrared spectrometer. The rigid main chain is substantially constant from room temperature to110℃, and the distorted deformation does not appear until the temperature reaches higher than110℃, and finally the main chain of plastic crystal is softened rapidly at the melting point and falls in disordered state. As for the flexible alkyl side chain, it does not form a crystalline state, but a liquidlike state at atmosphere temperature. While the gtt (end group) configuration content changes little with temperature, the gtg’configuration content rises from room temperature, along with the decrease of the all-trans configuration content. But all the changes are reversible. So we summarized the results from XRD and UV absorption spectrum, and point out that the main effects of thermal annealing is to improve chain order and film crystallinity, which are attributed to the molecular rotational movement of the crystallization region in the thermal annealing process. (4) Compared with the dynamic structure in the atmospheric pressure, the thiophene main chain and alkyl side chain exhibit inverse rule in high-pressure nitrogen. For rigid main chain, high pressure nitrogen suppressed its structure evolution to a small extent in thermal annealing. For flexible alkyl side chain, the high-pressure nitrogen gas exacerbates the degree of distortion with temperature. Despite the phenomenon above, the XRD patterns, UV-Vis absorbance spectra and carriers mobility showed no differences for the films annealed at150℃under4.0MPa nitrogen pressure and atmospheric pressure.