Photoluminescence Enhancement in Silica‐Confined Ligand‐Free Perovskite Nanocrystals by Suppression of Silanol‐Induced Traps and Phase Impurities

The detriments of intrinsic silanol groups in mesoporous silica to the photoluminescence (PL) of lead halide perovskite nanocrystals (LHP NCs) confined in the template have never been realized and clearly elucidated. Here, we disclose that the silanol induced Cs+ and Br‐ deficiencies prompt the generation of traps and CsPb2Br5 impurities. The temperature dependent PL spectra verify the higher energetic barrier of trap states in CsPbBr3 NCs confined in silanol‐rich mesoporous silica. Femtosecond transient absorption spectra reveal the trapped state mediated broadband photoinduced absorption and long‐lived decay pathway of CsPbBr3 NCs in silanol‐rich templates. Remarkable improvement (maximal 160‐fold) in PL quantum yields is realized by simple silanol elimination. This work demonstrates the detrimental effects of silanol sites on the PL properties of LHP NCs impregnated in mesoporous silica, and provides new perspective for ligand‐free synthesis of high‐quality LHP NCs in mesoporous templates by facile impregnation for practical applications.