## 3 Results and Discussion  
To enhance stability, single silica-coated CsPbI\({}_{3}\) PeQDs (SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs) were designed and synthesized through a hot injection method using APTES as the SiO\({}_{2}\) source. The synthesis procedures and chemical structures of APTES, OAm, and OA are shown in Figure 1. Specifically, the APTES was injected into the mixture of PbI\({}_{2}\), I\({}_{2}\), OAm, and OA precursor in toluene solution at 105 \({}^{\circ}\)C under N\({}_{2}\) protection and maintained at this temperature for 5 min to remove oxygen and moisture. After the preheated Cs-oleate precursor was injected into the above mixture to initiate nucleation and growth, the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs were obtained by purification. By changing the feeding content of APTES from 0, to 2, to 4, to 6 mmol, the experimental conditions were optimized; and the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs refer to that with 4 mol APTES precursor without special notes. Through the interaction between APTES and the CsPbI\({}_{3}\) PeQD surface, APTES was hydrolyzed to form SiO\({}_{2}\), which was expected to improve both the optical properties and the stability. We did not add extra water into the reaction mixture, but some water nonetheless remained in the three-necked flask or toluene after drying. Furthermore, during the transfer process, but after the hot injection, the solution came into contact with air, leading to APTES hydrolysis. To investigate the influence of SiO\({}_{2}\) coating on the morphology of CsPbI\({}_{3}\) PeQDs, TEM technology was used. Figure 2a shows the TEM of OAm-CsPbI\({}_{3}\) PeQDs, which indicates that the shape of OAm-CsPbI\({}_{3}\) PeQDs is cubic, with an average side length of 6.31 \(\pm\) 1.21 nm, which was found by counting 120 particles (Figure S1a in Supplementary Materials). The shape of the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs is also cubic, without aggregation, with a more uniform size distribution and an average side length of 10.07 \(\pm\) 0.93 nm (Figure S1b in Supplementary Materials), which is larger than that of OAm, indicating that the SiO\({}_{2}\) coating contributes to an increase in the size of the CsPbI\({}_{3}\) PeQDs, which is due to the changed acid\(-\)base interaction caused by the addition of APTES [38,46]. Surprisingly, TEM results also verify that one SiO\({}_{2}\) particle contains only one CsPbI\({}_{3}\) PeQD particle, which is beneficial to the maximum of PLQY. High-resolution TEM (HRTEM) images of the OAm- and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs were obtained and are displayed in Figure 2c,d, respectively. It can be seen that both interplanar distances are 0.58 nm, signifying their good crystallinity and that the attaching of SiO\({}_{2}\) onto CsPbI\({}_{3}\) PeQDs exerts no effect on the crystallinity. In order to further evaluate the effect of SiO\({}_{2}\) on the crystallinity, XRD technology was employed on CsPbI\({}_{3}\) PeQDs. Figure 3a shows the XRD patterns of the OAm- (black line) and SiO\({}_{2}\)- (red line) CsPbI\({}_{3}\) PeQD powders on glass substrates by drop-casting the inks. Both the CsPbI\({}_{3}\) PeQDs correspond well to the \(\alpha\)-phase CsPbI\({}_{3}\), and the diffraction peaks at 14.3\({}^{\circ}\), 20.2\({}^{\circ}\), 24.7\({}^{\circ}\), 28.8\({}^{\circ}\), 32.4\({}^{\circ}\), 35.6\({}^{\circ}\), and 40.1\({}^{\circ}\) can be attributed to the (100), (110), (111), (200), (210), (211), and (220) planes, respectively, which is indicative of good crystallinity. Specifically, according to Bragg's law, the interplanar distance of the (100) plane is 0.58 nm, which is in agreement with the HRTEM results. Furthermore, the diffraction peaks of SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs at 14.3\({}^{\circ}\) and 28.8\({}^{\circ}\) are higher and narrower than the OAm ones, indicating the larger size of the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, which is consistent with the size results from the TEM images.