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Low photoluminescence quantum yield (PLQY) and spectra instability, the two most difficult challenges in blue‐emitting CsPbBrxCl3−x NCs, have not yet been solved. Quickly controlling the reaction thermodynamics is crucial to enhance crystallinity, thus PLQY and spectra stability, but it has been ignored until now. An ultrafast thermodynamic control (UTC) strategy is designed by utilizing liquid nitrogen to instantaneously freeze the superior crystal lattices of CsPbBrxCl3−x NCs formed at high temperature. The average cooling rate exhibits a 33‐fold increase compared to conventional ice‐water cooling (from 1.5 to 50 K s−1). This UTC can make the reaction thermodynamic energy of the system lower than the threshold very quickly. Therefore, abrupt termination of further crystal growth can be achieved, which also avoids additional nucleation at low temperature. With the assist of defect passivation, the final blue‐emitting CsPbBrxCl3−x NCs exhibit an absolute PLQY of 98%, representing the highest value in Pb‐based blue perovskites to date. More importantly, they exhibit superior spectra instability. This UTC strategy not only represents a new avenue to synthesize perovskite NCs with excellent crystal quality and ultrahigh PLQY, but also provides a good reference to deal with the recognized bottleneck of spectra instability. [ABSTRACT FROM AUTHOR]

All-inorganic halide perovskites have attracted great attention by virtue of the merits of bright emission, tunable wavelength and narrow-band emission. Despite the excellent optical features, all-inorganic halide perovskite materials have suffered from intrinsic instability, which has limited their applications in various optoelectronic devices. To mitigate the intractable issue, we demonstrated the CsPbBr3 nanoparticles decorated with smaller SiO2 nanocrystals to passivate the surface defects; SiO2 nanoparticles were applied as a barrier layer to maintain the optical property and enhance environmental stability. A facile in situ method was proposed to prepare CsPbBr3/SiO2 nanocomposites, in which an environmental ethanol/water solvent system was needed with the addition of tetraethyl orthosilicate (TEOS) as a silicon precursor. The obtained CsPbBr3/SiO2 nanocomposites have better optical characteristic and stability than bare CsPbBr3 nanoparticles. Even 70% photoluminescence intensity of as-prepared CsPbBr3/SiO2 nanocomposites can be maintained after 168 h storage in ethanol. This newly developed synthesis will open up a new route for the fabrication of optoelectronic devices in an environmentally friendly way, and the as-obtained perovskite materials with improved stability will make them great potential for multifunctional optoelectronic devices. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite nanocrystals have held great promise as incredibly effective luminescent materials and also have been synthesized efficiently by room temperature approaches. Toluene, a high toxicity solvent, is often used as a valid antisolvent in ligand-assisted reprecipitation strategy, which badly restricts the commercial application of this convenient method. Here, aiming to address the toluene toxicity issue, the low toxic tetraethyl orthosilicate (TEOS) is employed as a new alternative antisolvent to achieve high uniform and composition dependent luminescent all-inorganic perovskite Cs 4 PbX 6 (X = I, Br, Cl) combined with CsPbX 3 (X = I, Br, Cl) nanocrystals with tunable emission large-span wavelengths (626–437 nm) and remarkably narrow full width at half-maximum (FWHM) monochromaticity (down to 19 nm). Meanwhile, the ratio of CsBr to PbBr 2 is proved to be a critical factor to control the crystalline phase of the resulting perovskite nanocrystals. Additionally, one monochromatic light-emitting diode (LED) lamp with brightly pure green emission is fabricated based on bromine-based perovskite nanocrystals. This newly developed low toxicity antisolvent synthesis (LTaS) is suitable candidate for commercial production in an environmentally-friendly way, and the as-obtained perovskite materials with superior optical merits will be brought to the forefront of lighting and displays. [ABSTRACT FROM AUTHOR]

• Air-stable MAPbI 3 was fabricated by solvent dose control and ligand regulation. • The MAPbI 3 quantum dots exhibit high photoluminescence quantum yield up to 80%. • The quantum yield was still at 74% of its original value after 20 days. • The strategy is also suitable for preparing color-tunable MAPbX 3 (X = Cl, Br, I). Methyl-ammonium lead iodide (MAPbI 3) perovskite quantum dots (QDs) have emerged as a promising material for photoelectronic, however, they usually suffer intrinsically from the environmental instability and low photoluminescence quantum yield (PLQY), which will seriously impede their commercial applications. Here, we report an internal-external combination strategy by lowering the dose of good solvent and reducing the chain length of amine ligand to simultaneously enhance the air stability and PLQY of MAPbI 3 QDs. The low-dose solvent can effectively reduce internal iodine vacancies defects and external residual solvent molecules, meanwhile, the faster and denser assembly of nimble short-chain (SC) ligand on the MAPbI 3 QDs surface can helpfully enhance the external surface passivation. As a result, compared to MAPbI 3 QDs synthesized by traditional ligand-assisted reprecipitation (LARP) method, the air stability and PLQY of which are improved by more than four orders of magnitude (from a few minutes to dozens of days) and nearly two times (from 42% to 80%) prepared by our strategy. Besides, this strategy can widely tune the color of MAPbX 3 (X = Cl, Br, I) QDs from 388 to 735 nm through regulating components. This internal-external combination strategy can provide some beneficial enlightenment for preparing long-term air-stable hybrid perovskite QDs with high PLQY, which drastically driving their commercial applications. [ABSTRACT FROM AUTHOR]

Flexible photodetectors (PDs) are attracting more attention due to their promising applications in wearable optoelectronic devices, bendable imaging sensors, and implantable optoelectronics. For the easy‐processable technology of massively fabricating PDs, instead of the expensive and complex high‐vacuum technique, the well‐matched work function of their active materials is essential. Herein, all‐sprayed‐processable and large‐area PDs are demonstrated on common paper based on two‐dimensional (2D) CsPbBr3 nanosheets and conductive Ti3C2Tx (MXene). Ascribed to the superior conductivity of MXene, high crystallinity of 2D CsPbBr3, and their well‐matched work function, the as‐prepared PDs exhibit an outstanding on/off current ratio up to 2.3 × 103 and a remarkable photoresponse as fast as 18 ms. Specifically, the detectivity (D*) of 6.4 × 108 Jones and responsivity (R) of 44.9 mA W−1 under a bias of 10 V are achieved. Besides, after bending 1500 cycles, the as‐prepared PDs can still maintain the excellent flexibility and stability. Based on this, a superior‐quality and large‐area 1665 pixel sensor in 72 cm2 (≈24 units cm−2) is developed, and it can clearly transmit the image of "0" to realize the photocommunication function. This work provides a low‐cost method of massively producing the flexible large‐area PDs for wearable optoelectronic devices and expanded photocommunication. The on‐paper flexible photodetectors based on 2D perovskite nanosheets and Ti3C2Tx (MXene) as the active materials and electrode materials by all‐spraying method are demonstrated. The low‐cost photodetectors have high stability, flexibility, photoelectric performance, and can effectively realize the optical communication function of image sensing by large‐area arrays. This technique can be potentially expanded to other optoelectronic devices. [ABSTRACT FROM AUTHOR]