# Synthesis, Structure and Photoluminescence Properties of 2D Organic-Inorganic Hybrid Perovskites
## 3 Results and Discussion
### Absorption Spectrum  
Figure 6 shows the UV-Vis absorption spectra of the perovskites (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbCl\({}_{4}\), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) and (C\({}_{4}\)H\({}_{9}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\). The absorption peaks are located at 346 nm (3.47 eV), 392 nm (3.16 eV), 516 nm (2.33 eV) and 416 nm (2.96 eV), respectively. It can be seen that the absorption spectra of (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbCl\({}_{4}\), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) have a redshift. When the organic part remains unchanged, the absorption peak of the inorganic part increases, with the atomic radius of chlorine, bromine and iodine increasing in turn. As the atomic radius of chlorine, bromine and iodine increases in turn, the framework of PbX\({}_{2}\) in the inorganic layer increases in turn, and the band gap of PbCl\({}_{2}\), PbBr\({}_{2}\) and PbI\({}_{2}\) in the inorganic part decreases in turn, resulting in the decrease of exciton binding energy in turn, so the exciton absorption peak shifts red. Therefore, the absorption spectrum of (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbCl\({}_{4}\), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) show redshift [36]. Figure 5: (**a**) The bright field TEM images, (**b**) HR-TEM images and (**c**) SAED pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbCl\({}_{4}\) nanosheets; (**d**) the bright field TEM images, (**e**) HR-TEM images and (**f**) SAED pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbB\({}_{4}\) nanosheets; (**g**) the bright field TEM images, (**h**) HR-TEM images and (**i**) SAED pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) nanosheets; (**j**) the bright field TEM images, (**k**) HR-TEM images and (**l**) SAED pattern of the perovskite (C\({}_{4}\)H\({}_{9}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) nanosheets. Figure 6: The UV-Vis absorption spectrum of (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbCl\({}_{4}\) (black curve), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) (red curve), (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) (blue curve) and (C\({}_{4}\)H\({}_{9}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) (pink curve). The absorption peaks of (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{4}\)H\({}_{9}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) also show a redshift in Figure 6. For (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{4}\)H\({}_{9}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) with the same inorganic layer PbBr\({}_{2}\), it can be found that the forbidden band width of perovskite samples increases with the increase of the carbon chain length. We know that organic components have little contribution to this energy band. The valence band top and conduction band bottom of perovskite generally come from atomic orbitals in inorganic components. It shows that the organic components contribute little to this energy band, and that the valence band tops and conduction band bottoms of perovskites generally come from atomic orbitals in inorganic components. However, because the short chain has a stronger push electron effect than the long chain, the charge distribution between the inorganic and organic components changes, leading to the hydrogen bond interaction between the organic and inorganic layers changes.