## 3 Results and Discussion
Both TEM and XRD data show that SiO\({}_{2}\) has no effect on the crystal structure and morphology of CsPbI\({}_{3}\) PeQDs but does increase size. To examine the capping ligand of the CsPbI\({}_{3}\) PeQDs, FTIR technology was used. Figure 3b shows the FTIR spectra of the OAm- (black line) and SiO\({}_{2}\)- (red line) CsPbI\({}_{3}\) PeQD powders. For the OAm-CsPbI\({}_{3}\) PeQDs, the strong absorption bands centered at 2923 and 2854 cm\({}^{-1}\) are related to the asymmetric and symmetric tensile vibration of \(-\)CH\({}_{2}\)[47], while the weak absorption peaks at 1710 and 1640 cm\({}^{-1}\) correspond to the stretching vibrations of C=O and bending vibrations of \(-\)NH\({}_{2}\) groups, respectively. By checking the chemical structures of capping ligands (Figure 1c), we found that the C=O and \(-\)NH\({}_{2}\) groups are exclusive of OAm and OA, respectively. This indicates that both OAm  
Figure 1: Schematic illustration for the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs: (**a**) synthesis procedures; (**b**) hydrolysis diagram; and (**c**) chemical structures of the capping ligands. and OA exist on the surface of CsPbI\({}_{3}\) PeQDs. For the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, the bending vibrations of \(-\)NH\({}_{2}\) group strengthens, indicating the occurrence of APTES on CsPbI\({}_{3}\) PeQDs (see chemical structure of APTES in Figure 1c). Furthermore, new absorption peaks at 1124 cm\({}^{-1}\) and 1037 cm\({}^{-1}\) appear and can be assigned to the vibrations of Si-O-Si and Si-O-C groups, respectively, proving the hydrolysis of APTES into SiO\({}_{2}\) on CsPbI\({}_{3}\) PeQDs [48]. This signifies that, for the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, the capping ligands are OAm, OA, and APTES. To further confirm the existence of SiO\({}_{2}\), X-ray photoelectron spectroscopy (XPS) technology was used on the CsPbI\({}_{3}\) PeQDs powders. In the XPS full spectra (Figure S2, Supplementary Materials), it can be seen that the signals of Cs 3d, Pb 4f, I 3d, C, N, and O appear on both the OAm- and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, but the Si 2p signal only appears on the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs (high-resolution XPS spectra in Figure 3c), which is consistent with the EDX results in Figure S4 (Supplementary Materials). This indicates that the capping ligands for OAm-CsPbI\({}_{3}\) PeQDs are OAm and OA only, but the capping ligands for the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQD surface are OAm, OA, and APTES, which is consistent with the FTIR results. Furthermore, the ratios of N:Pb and O:Pb increases (Figure 3d), which confirms the appearance of APTES. In addition, the ratio of I:Pb increases from 3.73 for OAm-CsPbI\({}_{3}\) PeQDs to 4.39 for SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, signifying that a richer environment is provided by the inclusion of an SiO\({}_{2}\) coating, which indicates a more effective defect passivation and thus higher PLQY [49]. Figure 2: TEM images of the (**a**) OAm- and (**b**) SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs. HRTEM images of the (**c**) OAm- and (**d**) SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs. Based on the above results, we anticipate that the extra SiO\({}_{2}\) coating will endow the CsPbI\({}_{3}\) PeQDs with highly efficient emission. To verify this point, the UV-vis absorption and PL spectra were obtained with different APTES (Figure S5 in Supplementary Materials). From these results, we observed that with the increase of APTES from 0 to 6 mmol, the PLQY first enhances and then decreases with the maximum PLQY obtained at 4 mmol APTES. Furthermore, during the whole process, the UV-vis absorption and PL spectra shift to long wavelength. Specifically, the UV-vis absorption of OAm-CsPbI\({}_{3}\) PeQDs (0 mmol APTES precursor) and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs (4 mmol APTES precursor) in Figure 4a shows that absorption red shifts from 593 nm to 610 nm due to the SiO\({}_{2}\) coating. The PL spectra in Figure 4b also shows a red shift from 668 nm to 678 nm due to the SiO\({}_{2}\) coating.