NiBr₂-Treated CsPbI₃ Nanocrystals with Stability and Tunable Bright Luminescence for Light-Emitting Devices

It is well known that red-emitting cesium lead iodide (CsPbI3) nanocrystals (NCs) are unstable under light and humid conditions. This has greatly limited their application. Especially, NCs are prone to phase transformation below 300 °C. In this paper, the photoluminescence (PL) properties and stability of CsPbI3 NCs prepared by a hot injection method were improved via ion exchange reactions. Compared with pure CsPbI3 NCs, the PL quantum yield of CsPbI3 NCs increased 2 times (80%) and the stability increased 4 times under room light irradiation after treating with a NiBr2 solution. In addition, the PL intensity and stability of CsPbI3 NCs were also improved by treating with cadmium bromide and hydrogen bromide solutions. This confirms that both Br and Ni ions play important roles in increasing the stability. Because of the introduction of Br ions, tunable PL spectra from yellow to dark red were observed. This result depicts the broad application of NCs. After ion exchange reactions, the surface defects of CsPbI3 NCs were passivated by Br ions. However, the initial crystal structure of CsPbI3 NCs remained unchanged. Because of tunable PL properties and high stability, the NCs will be used for solar cells, light-emitting devices, and photodetectors.