Bifunctional Passivation Strategy to Achieve Stable CsPbBr₃ Nanocrystals with Drastically Reduced Thermal-Quenching

The thermal quenching behavior (temperature-dependent luminescence) has severely hindered the practical applications of CsPbX₃ nanocrystals. Here, we find that a simple surface treatment using ammonium hexafluorosilicate (AHFS, (NH₄)₂SiF₆) can drastically reduce the thermal quenching of CsPbBr₃ nanocrystals (CPB-NCs) while enhancing their photostability. The AHFS-treated sample sustains 90% of its original emission intensity as the temperature rises to 353 K, which is much better than that (17%) of the pristine sample. Meanwhile, the thermally stable AHFS-treated sample could maintain 93% of its initial PL emission after a 450 nm LED illumination of 53 h. Structural and surface characterizations indicate that the hydrolyzable AHFS absorbed on the surface could lead to a bifunctional passivation for CPB-NCs, through fluoride ions and its hydrolyzed product of silica, which can reduce the thermal quenching by limiting thermally activated carriers trapping into vacancies and block the attack from external environmental factors.