A-site FA+ engineering boosting photoluminescence efficiency and stability of cesium copper iodine (Cs3Cu2I5) perovskites

Abstract

Lead-free perovskites have attracted increasing attention owing to their excellent optoelectronic properties and non-toxicity in recent years. However, compared with those of Pb-based perovskites, the luminescence efficiency and stability of lead-free perovskites still need to be further improved. Here, we firstly propose an A-site engineering strategy to improve the luminescence performance of Cs₃Cu₂I₅via a facile and low-cost solution method. Through the incorporation of the formamidinium cation (FA⁺), the lattice defects in Cs₃Cu₂I₅ can be significantly reduced, thus reducing non-radiative recombination and improving luminous efficiency. The photoluminescence quantum yield (PLQY) of the optimized A-site FA⁺-engineered Cs₃Cu₂I₅ is increased to 95%, representing a 35.7% improvement. Furthermore, the stability of FA⁺-engineered Cs₃Cu₂I₅ can be greatly improved, as evidenced by the decay of photoluminescence (PL) intensity after storage for 30 days and repeated heating–cooling test under the ambient atmosphere. Finally, pure blue emission with the chromatic coordinates of (0.1692, 0.1215) is achieved by encapsulating 5% FA⁺-engineered Cs₃Cu₂I₅ phosphors on a UV LED chip. Our proposed A-site FA⁺ engineering strategy would highly promote Cs₃Cu₂I₅ towards industrial application.