Low-dimensional organic–inorganic hybrid metal halide materials have been extensively studied due to their excellent optoelectronic performances. Herein, by using the facile wet-chemistry method, we designed one new hybrid cadmium bromide of (H3AEP)2CdBr6·2Br based on discrete octahedral [CdBr6]4– units. Remarkably, the bulk crystal of (H3AEP)2CdBr6·2Br exhibits strong broadband orange–red light emission from the radiative recombination of self-trapped excitons (STEs) with a high photoluminescence quantum yield (PLQY) of 9%. Benefiting from the highly efficient luminescent performance, this 0D cadmium perovskite can be utilized as an excellent down-conversion red phosphor to assemble a white light-emitting diode, and a high color rendering index (CRI) of 93 is realized. As far as we know, this is the first orange–red light-emitting hybrid cadmium perovskite which promotes the full-color display in this system.

Hybrid metal halides are an emerging class of highly efficient photoluminescent (PL) materials. However, very few of them show reversible on−off PL switching under external stimuli and have the potential to perform as next-generation intelligent materials with applications in cutting-edge photoelectric devices. Herein, we report single crystal-to-single crystal (SC− SC) structural and PL transitions among three 0D hybrid antimony halides, namely, nonemissive α- 2), and red-emissive β-[DHEP]SbCl 5 (3), by a dynamic phononengineering strategy. The reversible SC−SC transformation between 1 and 2 is triggered by acetone or methanol, affording the reversible PL on−off switching. The transition between yellow-emissive and red-emissive solids is achieved by the reversible SC−SC transformation between 2 and 3 through the process of removal/adsorption of guest water molecules. Meanwhile, the 3 to 1 transition is performed by the introduction of methanol, which is accompanied by the quenching of red emission. Therefore, a triple-mode reversible PL off−on I −on II −off switching is realized in metal halide hybrids for the first time, including the off−on I (yellow), colortunable on I −on II (yellow-red), and on II −off (red) modes. More importantly, the reversible PL switching in 0D hybrid antimony halides make them suitable for successful applications in the protection and anti-counterfeiting of confidential information as well as in optical logic gates.

To fabricate stable neat FAPbI3 perovskite with a pure α‐phase (pure α‐FAPbI3) is important in the field of photovoltaic commercialization because of its better bandgap than its alloying counterpart with cesium (Cs) or methylammonium (MA) cations. In this study, the first vapor deposited pure α‐FAPbI3 thin film solar cell with a power conversion efficiency (PCE) over 20% is achieved by regulating the phase transition process. It is found that under high humidity conditions, a fast phase transition between high‐purity α‐ and δ‐phase FAPbI3 can be realized. Moreover, theoretical calculations interestingly reveal a phase transition shortcut induced by the abnormal volume contraction that is ascribed to the formation of double hydrogen bonds at a certain H2O concentration. Therefore, a high‐humidity post‐treatment strategy is proposed to fabricate α‐FAPbI3 solar cells with a champion PCE of 20.19% (0.1 cm2) and 18.91% (1 cm2), which is currently the highest recorded value in vapor deposited pure α‐FAPbI3 perovskite solar cells. This study helps to redefine the effect of a water molecule on FAPbI3 solar cells. In addition, the demonstrated scaling‐up possibility provides another perspective for fabricating uniform high‐performance pure α‐FAPbI3 perovskite solar cells.

Intelligent stimuli-responsive fluorescence materials are extremely pivotal for fabricating luminescent turn-on switching in solid-state photonic integration technology, but it remains a challenging objective for typical 3-dimensional (3D) perovskite nanocrystals. Herein, by fine-tuning the accumulation modes of metal halide components to dynamically control the carrier characteristics, a novel triple-mode photoluminescence (PL) switching was realized in 0D metal halide through stepwise single-crystal to single-crystal (SC-SC) transformation. Specifically, a family of 0D hybrid antimony halides was designed to exhibit three distinct types of PL performance including nonluminescent [Ph 3 EtP] 2 Sb 2 Cl 8 ( 1 ), yellow-emissive [Ph 3 EtP] 2 SbCl 5 ·EtOH ( 2 ), and red-emissive [Ph 3 EtP] 2 SbCl 5 ( 3 ). Upon stimulus of ethanol, 1 was successfully converted to 2 through SC-SC transformation with enhanced PL quantum yield from ~0% to 91.50% acting as “turn-on” luminescent switching. Meanwhile, reversible SC-SC and luminescence transformation between 2 and 3 can be also achieved in the ethanol impregnation–heating process as luminescence vapochromism switching. As a consequence, a new triple-model turn-on and color-adjustable luminescent switching of off–on I –on II was realized in 0D hybrid halides. Simultaneously, wide advanced applications were also achieved in anti-counterfeiting, information security, and optical logic gates. This novel photon engineering strategy is expected to deepen the understanding of dynamic PL switching mechanism and guide development of new smart luminescence materials in cutting-edge optical switchable device.

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