Enhancing stability of red perovskite nanocrystals through copper substitution for efficient light-emitting diodes

Highlights: • Highly stable and luminescent red perovskite CsPbBrI₂ NCs were achieved through copper substitution and halide-rich strategy. • Bond strength of Pb-I of CsPbBrI₂ NCs can be improved by the incorporation of Cu²⁺ ions. • The halide-rich Cu²⁺-substituted CsPbBrI₂ NCs shown excellent photoluminescence quantum yield (PLQY) and ultrastability. -- Abstract: Red perovskite nanocrystals (NCs) are important for efficient perovskite light-emitting diodes (PeLEDs). However, the implementation of these red perovskite NCs are hindered because of their low structural stability. In the present work, highly stable and luminescent red perovskite CsPbBrI₂ NCs were achieved through copper substitution and halide rich passivation strategy. Because the ion radius of Cu²⁺ (0.72 Å) is smaller than that of Pb²⁺ (1.19 Å), divalent Cu²⁺ cations can partly replace the Pb²⁺ ions in the lattice structure of CsPbBrI₂ NCs. We demonstrated that the incorporation of Cu²⁺ ions can enhance formation energy, cause a slight lattice contraction, and hence stabilize the cubic phase of these NCs. On the other hand, Cu²⁺-substituted CsPbBrI₂ NCs with higher luminescence were synthesized in a halide-rich passivation method. Benefiting from such an effective substitution and halide-rich strategy, these Cu²⁺-substituted CsPbBrI₂ NCs has shown excellent performance with photoluminescence quantum yield (PL QY) (up to 94.8%) and an improved stability. The highly stable and luminescent Cu²⁺-substituted CsPbBrI₂ NCs can function well as efficient light emitters toward the fabrication of high-performance red perovskite LEDs.