## 3 Results and Discussion
### Morphology Characterization  
Figure 4a,b shows the SEM images of the perovskites (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\). The perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) exhibits a layered stacking structure with grain size of 1-5 um, and the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) also exhibits a layered stacking structure with grain size of 2-8 um. SEM images of the perovskites (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) and (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) are consistent with those observed in the bright field TEM images.  
Figure 3: The XRD patterns of the perovskite powders (**a**) (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\); (**b**) (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\).  
Figure 2: The crystal structure of the perovskites (**a**) (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\); (**b**) (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\). The hydrogen atoms bonded to the carbon atoms are omitted for clarity.  
Figure 5a shows the bright field TEM images of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) nanosheets. The perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) displays a layered stacking structure with crystal geometry size of 600 nm. Figure 5b shows the HR-TEM images of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) nanosheets. It shows that the lattice plane has the spacing distance of 0.294 nm, with the growth direction along [100]. The selected area electron diffraction (CaED) pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) nanosheets is shown in Figure 5c, indicating the orthorhombic phase, space group Cmca, with a growth direction along [100]. Figure 5d shows the bright field TEM images of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) nanosheets. The perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) displays a layered stacking structure with crystal geometry size of 1 um. Figure 5e shows the HR-TEM images of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) nanosheets. It shows that the lattice plane has the spacing distance of 0.294 nm, with the growth direction along [100]. The selected area electron diffraction (CaED) pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) nanosheets is shown in Figure 5f, indicating the orthorhombic phase, space group Pbca, with a growth direction along [010].  
Figure 5: (**a**) The bright field TEM images, (**b**) HR-TEM images and (**c**) Selected area electron diffraction (SAED) pattern of the perovskite (C\({}_{6}\)H\({}_{5}\)CH\({}_{2}\)NH\({}_{3}\))\({}_{2}\)PbBr\({}_{4}\) 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\({}_{3}\))\({}_{2}\)PbI\({}_{4}\) nanosheets.