Low photoluminescence quantum yield (PLQY) and spectra instability, the two most difficult challenges in blue-emitting CsPbBr x Cl 3−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 CsPbBr x Cl 3−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 CsPbBr x Cl 3−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.

All-inorganic cesium lead halide (CsPbX 3 , X = Cl, Br, and I) perovskite nanocrystals (NCs) have gained increasing attention in recent years, due to their excellent optical and electronic properties that are critical in the fabrication of efficient optoelectronic [1] and photovoltaic devices. [2] Currently, the external quantum efficiency (EQE) of perovskite light-emitting diodes (LEDs) has exceeded 20% [1d,e] while the perovskite solar cells have recently reached a power conversion efficiency (PCE) of 23.7%. [3] However, the major obstacle to future commercialization of perovskite NCs is their inherent vulnerability due to their ionic nature. [4] Therefore, perovskite NCs will decompose fast when exposed to ambient, especially in the presence of water or even in a moist environment. [5] But the appearance of water is inevitable during the process of materials synthesis and devices fabrication, which will badly influence the device stability and performance. So, the intrinsic water stability improvement of all-inorganic perovskite plays a key role to effectively enhance the long-time stability of perovskite materials and enormously promote the commercial applications of perovskite-based optoelectronic and photovoltaic devices.To overcome the poor water stability of perovskite NCs arising from their intrinsically high ionic character, many strategies have been developed. Typically, the substitution of the more stable ligands for the commonly used oleic acid (OA) and oleylamine (OLA) can suppress the degradation and maintain the crystal structures in water or other polar solvent. [6] In addition, polymer materials can effectively encapsulate perovskite NCs and avoid them directly contact with the external environment, which ensure the high environment stability especially superior water resistance of the peovskite-polymer composites. [7] Moreover, embedding perovskite NCs into inorganic matrix such as ionic salt, metallic oxide and silica also can obtain relatively ideal environment stability. [8] Although all of these works remarkably enhance the water stability of perovskite materials, these strategies mainly focus on isolating the materials from the external environment but not intrinsically improving its water stability. And also, these isolated materials will have a negative effect on charge transfer ability. Therefore, to develop the novel perovskite materials with both long-term intrinsic water stability and good charge transport ability is extremely urgent for optoelectronic and photovoltaic devices.All-inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water-stable all-inorganic quasi-2D CsPbBr 3 nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these u...

Figure 4. Characterization of the stability of the CsPbCl 3 MCFs and CsPbCl 3 MCFs-based UV-PDs. a) Comparison of the powder XRD patterns of the CsPbCl 3 MCFs freshly prepared and after storage in air environment for 5 months. b) Normalized IT curve of the CsPbCl 3 MCF UV-PDs under continuous and periodic (inset) 365 nm light illumination.

Single crystalline perovskites with long carrier lifetime, large carrier mobility and high atomic number emerge as highly sensitive X-ray detection materials. To precisely control its growth for high-quality perovskites single...