Molecular-Weight-Directed Confinement Growth of CsCu2I3@PEG Nanocrystals: Morphology Control, Ultrastable Luminescence, and Multilevel Thermal Encryption for High-Efficiency LEDs

Abstract

Metal halide perovskites have attracted substantial interest in lighting and display technologies in recent years. However, their commercial viability remains limited by poor stability and the toxicity of lead, underscoring the urgent need for efficient and environmentally friendly alternatives. Copper-based perovskites have emerged as promising candidates due to their abundant raw materials, low cost, excellent solution processability, and compatibility with low-temperature synthesis. In this study, we systematically investigate the influence of poly(ethylene glycol) (PEG) molecular weight on the structural, optical, and stability characteristics of CsCu₂I₃ perovskite composites through a molecular-weight engineering strategy. Furthermore, we demonstrate their innovative applications in high-efficiency light-emitting devices (LEDs) and dynamic information encryption. Using a room-temperature antisolvent method, we achieved tunable interactions between PEG and the perovskite material, from surface coordination at low PEG molecular weights to internally confined growth at high molecular weights, via ion–dipole interactions between PEG chain −O– groups and Cu⁺ ions. UV–vis absorption and Raman spectroscopy reveal that strong Cu–O coordination in high-molecular-weight PEG effectively suppresses nonradiative recombination, yielding a photoluminescence quantum yield (PLQY) of 81.86% for the Mn = 6 M composite. Stability assessments show that this composite retains over 90% of its initial performance under harsh conditions. Moreover, yellow-emitting LEDs based on the Mn = 6 M composite exhibit an extrapolated operational half-life of 110 days, with only a 13.6% efficiency decline after 30 days of continuous operation. Leveraging the distinct thermal responses of composites with gradient PEG molecular weights (1 K–6 M), we also developed a quadruple-level dynamic encryption system. This system utilizes programmable temperature control to enable multilevel information decryption governed by temperature–time dual-variable coordination.