Controlling the growth of a SiO2 coating on hydrophobic CsPbBr3 nanocrystals towards aqueous transfer and high luminescence†
Silica coating can effectively solve the stability issue of lead halide perovskite nanomaterials. However, it is difficult to achieve aqueous SiO2 coating on hydrophobic CsPbBr3 nanocrystals (NCs). In this paper, the hydrolysis process of tetramethoxysilane was controlled to get a homogeneous SiO2 coating or a NC/SiO2 Janus structure. In step 1, the Cs4PbBr6 NCs were silanized using partially hydrolyzed tetramethoxysilane (PH-TMOS). During this process, the Si–OH groups which came from PH-TMOS were absorbed onto the surface of the Cs4PbBr6 NCs with the removal of hydrophobic oleic acid (OA) ligands. In step 2, phase transformation from Cs4PbBr6 to CsPbBr3 occurred owing to the injection of water. Meanwhile, further hydrolysis of TMOS took place and generated cross-linked Si–O–Si. Because the silanization in step 1 created lots of growth sites, the condensation of SiO2 was not limited to the interface between water and hexane. After growing for 12 h, the fully covered CsPbBr3@SiO2 capsules were prepared. The anion exchange reactions of the CsPbBr3@SiO2 capsules were studied. Only one even and symmetric PL peak was apparent during the anion exchange process, which was different from the bare CsPbBr3 NCs. This result demonstrated that the SiO2 shell can act as a buffer layer to block the direct contact of CsPbBr3 with the excess PbBr2 precursor in solution. Compared with the CsPbBr3 NCs, CsPbBr3@SiO2 showed better stability in polar solvent and air. A bright green emission was also observed under UV light after 90 days. The successful preparation of CsPbBr3@SiO2 capsules with enhanced stability paves the way for the further development of lead halide perovskite nanomaterials.