Highly stable lanthanide-doped CsPbI 3 perovskite nanocrystals with near-unity quantum yield for efficient red light-emitting diodes.

CsPbI 3 perovskite nanocrystals (NCs) are gaining popularity as promising photoactive materials for optoelectronic devices. However, their poor phase stability has caused substantial limitations in their practical application. Herein, the small-sized rare earth La cation is strategically introduced to fundamentally improve the NC phase stability against the environment, heat, and UV radiation by the partial substitution of Pb ions to suppress structural distortion and increase the formation energy. The strong interaction between La and I of the octahedra has been demonstrated to enable the effective suppression of the trap states, which promotes strengthened radiative recombination for a near-unity photoluminescence quantum yield (PLQY) of 99.3%. High energy bands have also been found for the La-doped NCs to narrow down the energy barrier for efficient hole injection. The superior optoelectronic properties of La-doped NCs promote great improvements in the perovskite light-emitting diode (PeLED) performances with a 5-fold improvement in external quantum efficiency (EQE) from 1.19 to 6.01% and 2-fold longer lifetime from 1451 to 2956 s. This work provides an effective method for small-sized metal ion-doped CsPbI 3 NCs to realize high emission efficiency and phase stabilization for efficient PeLEDs.