Guanidium iodide treatment of size-controlled CsPbI3 quantum dots for stable crystal phase and highly efficient red LEDs

Abstract

The optoelectronic properties of lead-halide perovskite quantum dots (QDs) can be tuned according to their halogen composition ratio and quantum size effect. However, the pure red emission of CsPbI3 QDs exhibits poor phase stability, thereby resulting in a phase transition to a nonphotoactive yellow phase at room temperature. These phase instabilities are accompanied by crystal strain and instability of the QD surface, which induce ion diffusion and desorption. Herein, we demonstrate the precise size control and postsynthetic guanidinium iodide (GAI) treatment to stabilize the crystal phase of CsPbI3 QDs. These synergistic effect results in higher ambient photoluminescence stability and photostability than those of pristine QDs. More importantly, the CsPbI3 QD light-emitting diodes achieve excellent external quantum efficiency of 22.5% and longer operational stability of over 10 h by the synergy effect of QD size control and GAI treatment.