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Despite recent advances, it is still difficult to fabricate deep blue‐emitting perovskite light‐emitting diodes (LEDs) that are immune to the color instability caused by halide mixing. This is largely because it is still challenging to achieve bright, stable, pure bromide perovskite materials with deep blue emission. Here, a novel strategy is reported for synthesizing ultrasmall CsPbBr3 quantum dots (QDs) under ambient conditions. Precise size control is used to tune the peak emission wavelengths, via the confinement effect, from 433 to 501 nm. These ultrasmall QDs, with sizes of 2–6 nm, exhibit ultralow trap density and stable photoluminescence quantum yields up to 94%, particularly in the deep blue spectral region (440–465 nm). QD‐LEDs fabricated with these materials achieve an external quantum efficiency of 1.0% at 459 nm. The exceptional control of the emission properties demonstrated here suggests a new strategy for building stable, efficient blue QD‐LEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskite nanoplatelets (NPLs) have demonstrated excellent optical properties for light‐emitting applications and achieved tunable blue luminescence through thickness control. However, their translation into electronic devices has lagged behind due to poor colloidal and film stability. The main reason for this is the deprotonation of their surface‐capped ammonium passivating ligands, resulting in NPL aggregation. Here we report the first facile synthesis of amine‐free pure‐blue CsPbBr3 NPLs with outstanding thermal and light stability. This is achieved by utilizing an amine‐free phosphine oxide route with a surface capping molecule exhibiting large steric hindrance to prevent NPL aggregation. Two‐dimensional nuclear magnetic resonance (2D NMR) spectroscopy suggests slower ligand exchange in amine‐free NPLs compared to the conventional NPLs, which can be attributed to the strong binding strength of the designated ligand. Consequently, the amine‐free NPLs exhibited superior stability against radiation, heat and moisture. We further demonstrate the importance of acid‐base equilibrium in this amine‐free synthesis route. Through solvent neutralization and passivation with various alkali carbonates, the resulting NPLs attained near‐unity photoluminescence quantum yield (PLQY) and pure blue emission. [ABSTRACT FROM AUTHOR]

We report an intercluster compound based on co-deposition of the Au cluster [Au9(PPh3)8](NO3)3 and the fulleride KC60(THF). Electronic properties characteristic for a charge interaction between superatoms emerge within the solid state material [Au9(PPh3)8](NO3)3−x(C60)x, as confirmed by UV–VIS and Raman spectroscopy and I–V measurements. These emergent properties are related to the superatomic electronic states of the initial clusters. The material is characterized by Fourier-transform infrared spectroscopy, x-ray diffraction, Raman spectroscopy, and electrical measurements. Structural optimization and ab initio band structure calculations are performed with density functional theory to interpret the nature of the electronic states in the material; Bader charge calculations assign effective oxidation states in support of the superatomic model of cluster interactions. [ABSTRACT FROM AUTHOR]

Producing efficient blue and deep blue perovskite LEDs (PeLEDs) still represents a significant challenge in optoelectronics. Blue PeLEDs still have problems relating to color, luminance, and structural and electrical stability so new materials are needed to achieve better performance. Recent reports suggest using low n states (n = 1, 2, 3) to achieve blue electroluminescence in Ruddlesden–Popper (RP) perovskite films. However, there are fewer reports on the other quasi‐2D structure, Dion–Jacobson (DJ) perovksites, despite their highly desirable optical properties, due to the difficulty in achieving charge injection. To resolve this issue, herein, w e have mixed DJ phase precursors, propane‐1,3‐diammonium (PDA) bromide into RP phase perovskites and fabricated low‐dimensional PeLEDs. It is found that these specific precursors aid in suppressing both the low n (n = 1) and high n (n ≥ 4) quasi‐2D RP phases and is an effective strategy in blue‐shifting sky‐blue RP perovskites into the sub‐470 nm region. With optimization of the PDA concentration and device layers, it is achieved an external quantum efficiency of 1.5% at 469 nm and stable electroluminescence for the first deep blue PeLED to be reported using DJ perovskites. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have emerged as promising next-generation optoelectronic materials and achieved remarkable performances in both light-emitting diodes (LEDs) and solar cells (SCs). Despite reaching market demands such as high efficiencies and low manufacturing cost, the long-term stability of MHPs is still a massive challenge for commercialization. The presence of surface and bulk defects due to low-temperature solution-processable methods causes past degradation of perovskites. Here, we have investigated the passivation strategy for methylammonium lead iodide (MAPbI3) using resin polymer poly-[(phenylglycidyl ether)-co-formaldehyde] (PCF). PCF acts as a Lewis base additive with an electron-donating oxygen atom, which can coordinate with undercoordinated Pb2+ ions or NH3+ in perovskite crystals, developing smaller nanocrystalline grains with reduced defects. As a result, the PCF-passivated samples exhibit improved stability against moisture in a humid ambient environment (RH > 70%). Moreover, enhanced photoluminescence (PL) and lifetime were achieved without encapsulation. Furthermore, LEDs are demonstrated using the optimized PCF content. These results show the importance of resin polymers, which performs multiple functionalities such as nanocrystalline grain formation, defect passivation, and stability improvements for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Singlet fission is a process by which an organic semiconductor is able to generate two triplet excitons from a single photon. If charges from the triplets can be successfully harvested without heavy losses in energy, then this process can enable a single‐junction solar cell to surpass the Shockley–Queisser limit. While singlet fission processes are commonly observed in several materials, harvesting the resulting triplets is difficult and has been demonstrated with only a few transport materials. Here, transient absorption spectroscopy is used to investigate singlet fission and carrier transfer processes at the AgBiS2/pentacene (AgBiS2/Pc) heterojunction. The successful transfer of triplets from pentacene to AgBiS2 and the transfer of holes from AgBiS2 to pentacene is observed. Further singlet fission in pentacene by modifying the crystallinity of the pentacene layer and have fabricated the first singlet fission AgBiS2/Pc solar cell is enhanced. Singlet fission devices exhibit higher external quantum efficiency compared with the control devices, and thus demonstrating the significant contribution of charges from the singlet fission process. [ABSTRACT FROM AUTHOR]

CsPbX3 perovskite nanorods are known to display polarized emission, but also suffer from morphological and spectral instability. Here we synthesized CsPbX3 nanorods with polarized emission across the visible emission spectrum. We find that polarized emission is a function solely of the aspect ratio, as would be expected based on a purely dielectric effect. We then observe changes over time in the emission spectrum and polarization anisotropy as a function of the morphology. We find that, although these perovskite nanorods exhibit strongly polarized emission after synthesis, they suffer from serious morphological instability that reduces the polarization anisotropy over time. Worryingly, nanorods dispersed in anhydrous solvents, and even in a polymer matrix were observed to degrade in both inert environments and under ambient conditions. This results in a significant loss in polarized emission, and represents a problem for many intended applications. Finally, we evaluate several strategies for protecting these particles and find that silica encapsulation can be used to successfully prevent loss of polarized emission even under ambient conditions. [ABSTRACT FROM AUTHOR]

Lead-free ternary metal halides, especially cesium copper halides, have attracted tremendous research interest in the past two years owing to their outstanding optical properties, such as long photoluminescence (PL) decay lifetimes and high photoluminescence quantum yields (PLQYs). Recently, single crystals of potassium and rubidium copper halides have shown potential use in optoelectronics, and several synthetic methods have been reported for A2CuX3 (A = K, Rb; X = Cl, Br) single crystals. Here, we have successfully synthesized A2CuX3 micro- and nanocrystals by both anti-solvent recrystallization and hot injection methods, achieving size and shape control of these materials for the first time. A2CuX3 micro- and nanocrystals show near-UV to deep blue emission, with emission peaks ranging from 380 to 400 nm. Emission properties included Stoke's shifts over 100 nm, a fwhm of approximately 50 nm, a long PL lifetime, and high PLQYs, in particular for K2CuCl3, which shows near unity PLQYs. In addition, these materials can be used to produce white light along with previously reported CsCu2I3 nanocrystals. A mixed solution of K2CuCl3 and CsCu2I3 nanocrystals exhibits white light emission with a Commission Internationale de l'Éclairage (CIE) coordinate of (0.3456, 0.3304) and a color rendering index (CRI) of 75 at a color temperature of 4855 K. [ABSTRACT FROM AUTHOR]

Ternary copper halides have garnered significant interest for their bright, high quantum yield emission stemming from the radiative decay of self‐trapped excitons (STEs). Cesium copper halides have shown promise for use in optoelectronics, including light‐emitting devices (LEDs) for lighting and displays. To date several synthetic procedures for Cs3Cu2X5 (X = Cl, Br, and mixed Br/Cl) have been proposed for making nanocrystals, microcrystals, or polycrystalline thin films. Here, a synthetic method for making large single crystals (SCs) with millimeter dimensions in less than 30 min is presented. Phase pure mixed halide SCs are also produced and in‐depth structural analysis has been performed for the first time, definitively showing the site preferences for mixing chloride into the pure Cs3Cu2Br5 structure. Quantum yields for SCs of X = Cl and Br are 100% and 27% respectively, with long lifetimes and strong evidence of STE emission. This synthesis can be used to produce white light UV‐downconversion LEDs using ternary copper halides as the blue and green components along with the commercial red phosphor K2SiF6:Mn4+. These devices give a Commission Internationale de l'Éclairage (CIE) coordinate of (0.3327, 0.3342) and color rendering index of 90% at a color temperature of ≈5500 K. [ABSTRACT FROM AUTHOR]