A ligand strategy retarding monovalent copper oxidation toward achieving Cs3Cu2I5 perovskite emitters with enhanced stability for lighting

Abstract

0D copper-based perovskites (Cs₃Cu₂I₅) have fascinating optical properties, such as strong exciton binding energy, high photoluminescence quantum yield (PLQY) and large Stokes shifts from self-trapped excitons (STEs), which make them highly considerable candidates in the field of lighting. However, the stability of Cs₃Cu₂I₅ is compromised by the oxidation of Cu⁺ to Cu²⁺ during the storage or operation process. Here, we proposed a ligand engineering strategy to improve the stability of Cs₃Cu₂I₅via an organic molecule (ethylenediaminetetraacetic acid, EDTA) with multiple functional groups. The strong interaction between carboxyl groups and Cu⁺ was evidenced through FTIR and XPS, and it could retard monovalent copper oxidation. After storing for 90 days, the EDTA-engineered Cs₃Cu₂I₅ (EDTA-Cs₃Cu₂I₅) maintained its original crystalline structure, while the control Cs₃Cu₂I₅ exhibited an impurity phase. Through quantitative analysis, the content of Cu²⁺ in EDTA-Cs₃Cu₂I₅ was found to be 83.9% lower than that in control Cs₃Cu₂I₅. Benefiting from the inhibition of Cu⁺ oxidation, EDTA-Cs₃Cu₂I₅ exhibited improved light emission stability. For example, the optimized EDTA-Cs₃Cu₂I₅ retained 74.7% of the initial photoluminescence (PL) intensity after 90-day storage under ambient conditions, while the pure Cs₃Cu₂I₅ retained only 41.7%. Furthermore, EDTA could passivate defects and enhance the PL properties of the optimized Cs₃Cu₂I₅, which showed a PLQY of 94.7%, much higher than that of 71.4% for pure Cs₃Cu₂I₅. We further constructed a WLED based on the EDTA-engineered Cs₃Cu₂I₅, which showed CIE at (0.3238, 0.3354), a CRI of 91.7, and a T₅₀ of 361 h. The proposed EDTA ligand strategy provides a new way to regulate the light-emitting properties and stabilities of Cs₃Cu₂I₅ for future industrialization.