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

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 Cs(3)Cu(2)I(5)via 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.