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All‐inorganic CsPbX3 (X = Cl, Br, or I) perovskite thin films are attractive emissive layers for high‐performance light‐emitting diodes (LEDs) due to their precisely tunable bandgaps, excellent color purities, good stabilities, and solution processabilities. However, the fabrication of high‐quality CsPbI3−xBrx thin films is very challenging because the crystal growth of mixed halide CsPbI3−xBrx is in low controllability. Herein, a synergetic regulation strategy using fluorine polymer (Poly(vinylidene fluoride‐co‐hexafluoropropylene)) and a small amino acid molecule (L‐Arginine) is developed to fabricate high‐quality CsPbI3−xBrx thin films for efficient pure red perovskite LEDs. In the fabricated CsPbI3−xBrx thin film, the fluorine polymer plays a crucial role in confining CsPbI3−xBrx crystal size at the nanoscale and the small amino acid molecule acts as a passivation agent to reduce the trap‐state density. Under this synergetic effect, a uniform CsPbI3−xBrx thin film with a high photoluminescence quantum yield up to 40% can be obtained to fabricate an efficient pure red perovskite LED with a maximum external quantum efficiency of 4.5% and a maximum brightness of 3100 cd m−2. The reported synergistic regulation strategy will open a new avenue to fabricate efficient pure color CsPbX3 perovskite LEDs. [ABSTRACT FROM AUTHOR]

The exploration of lead‐free halide perovskite nanocrystals (NCs) with intriguing optical properties is highly desirable owing to the toxicity and instability of lead halide perovskite NCs. Here, a new kind of uniform lead‐free double perovskite Cs2NaBiCl6 NCs are reported as versatile hosts to accommodate ionic dopants for improving optical properties especially the photoluminescence (PL). In contrast to the low deep‐blue PL with a quantum yield of only 1.7% of the as‐synthesized pristine Cs2NaBiCl6 NCs, the PL of the Cs2NaBiCl6 NCs can be impressively regulated and enhanced via doping Ag+, Mn2+, or Eu3+ ions in the double perovskite lattices. The femtosecond time‐resolved transient absorption spectroscopy is adopted to unravel the PL enhancement mechanism of the ion doping in the Cs2NaBiCl6 NCs. For the Ag+‐doping, the excitonic absorption energy of the Cs2NaBiCl6 NCs can be tuned from 3.82 to 3.48 eV with the significant improvement of the PL quantum yield (PLQY) from 1.7% to 20%. The Mn2+‐doped Cs2NaBiCl6 NCs show broad orange–red emission peak centered at 585 nm with a PLQY of 3%, owing to the 4T1→6A1 transition of octahedrally coordinated Mn2+. Eu3+‐doped Cs2NaBiCl6 NCs are endowed with strong Eu3+5D0→7FJ (J = 1, 2) orange–red emission at 591 and 615 nm. [ABSTRACT FROM AUTHOR]

Abstract: Low‐dimensional organic–inorganic hybrid perovskites with controllable morphologies are attractive for high‐performance optoelectronic devices. In particular, the 1D organic–inorganic hybrid perovskite nanowires/nanobelts are promising for flexible photodetectors due to high photoresponsivity and strain endurance capability. Herein, a novel and large‐scale synthesis of (C4H9NH3)2PbBr4 organic–inorganic hybrid perovskite nanobelt achieved by the potassium ions assisted controllable crystal growth during the precipitation process in solutions is reported. The obtained (C4H9NH3)2PbBr4 perovskite nanobelts exhibit high‐efficient photoluminescence and superior stability under ambient conditions. Furthermore, these nanobelts are used as photoresponsive materials to fabricate flexible photodetectors, which show much higher switching ratio than that of photodetectors based on (C4H9NH3)2PbBr4 microplatelets. Attractively, after repeated bending for 1000 times, the nanobelt‐based photodetector only shows less than 10% decay in switching ratio in contrast to at least 40% of switching ratio decay for the microplatelets‐based photodetector. The reported potassium ion assisted large‐scale synthesis of (C4H9NH3)2PbBr4 nanobelts paves a new avenue for the application of organic–inorganic hybrid perovskites in flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]