Great successes have been achieved in developing perovskite light-emitting devices (LEDs) with blue, green, red, and near-infrared emissions. However, as key optoelectronic devices, yellow-colored perovskite LEDs remain challenging, mainly due to the inevitable halide separation in mixed halide perovskites under high bias, causing undesired color change of devices. In addition to this color-missing problem, the intrinsic toxicity and poor stability of conventional lead-halide perovskites also restrict their practical applications. We herein report the fabrication of stable yellow LEDs based on a ternary copper halide CsCu2I3, addressing the color instability and toxicity issues facing current perovskite yellow LED’s compromise. Joint experiment–theory characterizations indicate that the yellow electroluminescence originates from the broadband emission of self-trapped excitons centered at 550 nm as well as the comparable and reasonably low carrier effective masses favorable for charge transport. With a maximum luminance of 47.5 cd/m2 and an external quantum efficiency of 0.17%, the fabricated yellow LEDs exhibit a long half-lifetime of 5.2 h at 25 °C and still function properly at 60 °C with a half-lifetime of 2.2 h, which benefits from the superior resistance of CsCu2I3 to heat, moisture, and oxidation in ambient environmental conditions. The results obtained promise the copper halides with broadband light emission as an environment-friendly and stable yellow emitter for the LEDs compatible with practical applications.

Currently, the blue perovskite light-emitting diodes (PeLEDs) suffer from a compromise in lead toxicity and poor operation stability, and most previous studies have struggled to meet the crucial blue NTSC standard. In this study, electrically driven deep-blue LEDs (∼445 nm) based on zero-dimensional (0D) Cs3Cu2I5 nanocrystals (NCs) were demonstrated with the color coordinates of (0.16, 0.07) and a high external quantum efficiency of ∼1.12%, comparable with the best-performing blue LEDs based on lead-halide perovskites. Encouraged by the remarkable stability of Cs3Cu2I5 NCs against heat and environmental oxygen/moisture, the proposed device was operated in a continuous current mode for 170 h, producing a record half-lifetime of ∼108 h. The device stability was further verified by an aggressive thermal cycling test (300–360–300 K) and a 35-day storage test. Together with the eco-friendly features and facile colloidal synthesis technique, the 0D Cs3Cu2I5 NCs can be therefore regarded as a promising candidate for deep-blue LEDs applications.

Hydrochromic materials have attracted widespread attention in the fields of anti-counterfeiting because of their ability of the reversible light absorption and/or emission properties in response to water. Here, for the first it is demonstrated that the ternary copper halides Cs 3 Cu 2 I 5 nanocrystals (NCs) possess excellent hydrochromic properties. The prepared Cs 3 Cu 2 I 5 NCs films can dynamically extract and insert CsI by exposing/removing water to realize the reversible conversion between blue-emissive Cs 3 Cu 2 I 5 and yellow-emissive CsCu 2 I 3 . Interestingly, polymethyl methacrylate (PMMA) coated Cs 3 Cu 2 I 5 can effectively avoid the extraction of CsI and maintain long-term stability in the water. Further, the hydrochromic Cs 3 Cu 2 I 5 and water-resistant Cs 3 Cu 2 I 5 @PMMA are used as the inks to synergistically act on anti-counterfeiting information to achieve multiple encryption effects, which can clearly identify and authenticate the effective information after moisture decryption. Importantly, the pattern can be re-encrypted to the invalid pattern after water evaporation. In addition, the anti-counterfeiting pattern has excellent stability during repeated encryption/decryption conversion cycles, which can not only balance the accessibility of anti-counterfeiting information but also effectively improve the security of information. This new discovery may not only deepen the understanding of Cs 3 Cu 2 I 5 but also provide new options for the design of hydrochromic materials for anti-counterfeiting information.

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The rapid development of solid-state lighting technology has attracted much attention for searching efficient and stable luminescent materials, especially the single-component white-light emitter. Here, we adopt a facile ion-doping technology to synthesize vacancy-ordered double perovskite Cs 2 ZrCl 6 :Sb. The introduction of Sb 3+ ions with a 5s 2 active lone pair into Cs 2 ZrCl 6 host stimulates the singlet (blue) and triplet (orange) states emission of Sb 3+ ions, and their relative emission intensity can be tuned through the energy transfer from singlet to triplet states. Benefiting from the dual-band emission as a pair of perfect complementary colors, the optimum Cs 2 ZrCl 6 :1.5%Sb exhibits a high-quality white emission with a colorrendering index of 96. By employing Cs 2 ZrCl 6 :1.5%Sb as the downconversion phosphor, stable single-component white light-emitting diodes with a record half-lifetime of 2003 h were further fabricated. This study puts forward an effective ion-doping strategy to design single-component white-light emitter, making practical applications of them in lighting technologies a real possibility.