Deep-blue emissive Cs3Cu2I5 perovskites nanocrystals with 96.6% quantum yield via InI3-assisted synthesis for light-emitting device and fluorescent ink applications

Lead-free metal halide perovskites are promising materials for future optoelectronic application, which have recently attracted great attention for their environmental-friendliness and excellent light emission properties. However, the development of deep-blue emission lead-free halide perovskite nanocrystal is still far behind in performance in comparison with its red/green counterparts. Herein, the lead-free Cs3Cu2I5 nanocrystals are prepared via a modified hot-injection strategy. By adding InI3 as precursor, the synthesized Cs3Cu2I5 single-phase nanocrystals show a bright deep-blue emission peaked at similar to 440 nm, with a record high photoluminescence quantum yield (PL QY) up to 96.6% at an optimized InI3 content of 0.15 mmol. The InI3 additive contributes to the high PL QY through both iodide vacancy reparation of I- ions and size-controlled growth of In3+ ions. First principle calculations reveal that the broadband blue emission originates from self-trapped excitons in Cs3Cu2I5, which are formed due to the excited-state lattice expansion and Cu-I bond lengthening of [Cu2I5](3-) cluster under light excitation. The good stabilities of these Cs3Cu2I5 nanocrystals against heat, water, UV irradiation and environmental storage are also investigated experimentally and theoretically in detail. For application demon-stration, light-emitting devices are manufactured by using these Cs3Cu2I5 nanocrystals powder as phosphor, which exhibit good working stability with a half-lifetime over 300 h. Besides, the Cs3Cu2I5 nanocrystals solution is also utilized as fluorescent ink, and the printed patterns can maintain anti-counterfeiting features even after treatment by heating and long-term environmental storage, indicating the robustness of these Cs3Cu2I5 nano-crystals for potential anti-counterfeiting application.