WU Wenkui ¹, LU Yuchen ², LIANG Mengbiao ², XIE Zhixiang ¹, WANG Sanhai ³, CHEN Ting ²

(1. College of Chemistry and Life Sciences, Suzhou University of Science and Technology, Suzhou 215009, Jiangsu, China;

2. College of Materials Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009,

Jiangsu, China; 3. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:[Background and purposes] All-inorganic cesium lead halide perovskite NCs have garnered substantial attention, due to their exceptional PL properties, including high PLQY, long carrier lifetime, tunable emission wavelengths and high color purity. These characteristics render them highly suitable for applications in LEDs, display devices, solar cells and other optoelectronic fields. However, the intrinsic instability of these NCs, particularly their sensitivity to moisture, light, oxygen and temperature, severely limits their practical applications. To address this challenge, various strategies, including doping, surface modification and encapsulation, have been explored. Among these, surface encapsulation with SiO₂ has shown great potential in enhancing the stability and performance of CsPbX₃ NCs. This study is aimed to study the surface coating strategies of CsPbBr₃ NCs using SiO₂, thus optimizing the encapsulation process to improve their fluorescence stability and quantum yield.[Methods] CsPbBr₃ NCs were synthesized by using a supersaturation recrystallization method at room temperature. Lead bromide and cesium acetate were used as the precursors, while oleic acid and oleylamine served as capping ligands to control grain growth and surface properties of the NCs. DMF was employed as the solvent, and toluene was used as the antisolvent to induce recrystallization and precipitation of the CsPbBr₃ NCs. The molar ratio of Pb/Cs was systematically varied to identify the optimal composition for the fluorescence performance. Then, the synthesized CsPbBr₃ NCs were coated with a SiO₂ shell using TEOS as the silicon source. The effects of Pb/Cs molar ratios and TEOS dosages on fluorescence properties and stability of the CsPbBr₃@SiO₂ composites were evaluated. The samples were characterized by using XRD, TEM, FTIR, and PL spectroscopy, to reveal their crystal structure, morphology, chemical composition and optical properties.[Results] XRD results confirmed the successful formation of CsPbBr₃ and the presence of a SiO₂ shell in the composites. TEM results revealed that the CsPbBr₃ NCs were uniformly coated with a SiO₂ layer, with particle sizes ranging from 9 nm to 14 nm. FTIR data identified the characteristic Si-O-Si stretching vibrations, confirming the successful formation of the SiO₂ shell. PL spectra further validated the enhanced fluorescence properties of the CsPbBr₃@SiO₂ composites, as compared with the bare CsPbBr₃ NCs. The CsPbBr₃ NCs synthesized with a Pb/Cs molar ratio of 1.8 exhibited the highest PLQY of 46.9%. This ratio was identified as optimal for achieving the highest fluorescence performance. The PLQY of CsPbBr₃@SiO₂ composites was significantly enhanced when the TEOS/Pb molar ratio was optimized to 0.3, with a reaction time of 4 h. Under these conditions, the PLQY of the composites reached 62.2%. This improvement was attributed to the effective passivation of surface defects by the SiO₂ shell, which reduced non-radiative recombination and enhanced overall fluorescence efficiency. Stability of the CsPbBr₃ NCs was significantly improved by the SiO₂ coating. When exposed to ethanol for 30 min, the PL intensity of bare CsPbBr₃ NCs decreased to 21.5% of the initial value, while CsPbBr₃@SiO₂ composites retained 85.2% of their initial PL intensity. This result demonstrated that the SiO₂ shell effectively isolated the NCs from the polar solvent environment, thereby enhancing their stability.[Conclusions] An effective strategy for enhancing the fluorescence stability and PLQY of CsPbBr₃ NCs through SiO₂ coating was demonstrated. The optimized synthesis conditions, including a Pb/Cs molar ratio of 1.8 and a TEOS/Pb molar ratio of 0.3, led to a maximum PLQY of 62.2% for the CsPbBr₃@SiO₂ composites. The SiO₂ shell effectively passivated surface defects, reduced non-radiative recombination and provided a robust barrier against environmental degradation, significantly improving the stability of the NCs in polar solvents such as ethanol. These findings highlight the potential of CsPbBr₃@SiO₂ composites for practical applications in optoelectronic devices. Future work will focus on addressing the toxicity of lead-based perovskites and exploring more efficient encapsulation methods to further enhance material performance.

Key words: fully inorganic perovskite; CsPbBr₃ nanocrystalline; SiO₂ coating; quantum yield