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 ~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 demonstration, 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 nanocrystals for potential anti-counterfeiting application.