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Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large‐scale synthesis of CQDs with near‐unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical‐assisted synthesis of hexagon‐shaped CQDs (H‐CQDs) delivering near‐unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H‐CQDs originating from high symmetry results in nearly 100 % PLQY. The H‐CQDs also exhibited a high electron mobility of up to 0.07 cm2 V−1 s−1. These properties enable the H‐CQD‐based light‐emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m−2. This study represents a significant advance that CQDs‐based electroluminescent device can be utilized for potential display and lighting applications. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large‐scale synthesis of CQDs with near‐unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical‐assisted synthesis of hexagon‐shaped CQDs (H‐CQDs) delivering near‐unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H‐CQDs originating from high symmetry results in nearly 100 % PLQY. The H‐CQDs also exhibited a high electron mobility of up to 0.07 cm2 V−1 s−1. These properties enable the H‐CQD‐based light‐emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m−2. This study represents a significant advance that CQDs‐based electroluminescent device can be utilized for potential display and lighting applications. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

Perovskite‐based light‐emitting diodes (PeLEDs) are now approaching the upper limits of external quantum efficiency (EQE); however, their application is currently limited by reliance on lead and by inadequate color purity. The Rec. 2020 requires Commission Internationale de l'Eclairage coordinates of (0.708, 0.292) for red emitters, but present‐day perovskite devices only achieve (0.71, 0.28). Here, lead‐free PeLEDs are reported with color coordinates of (0.706, 0.294)—the highest purity reported among red PeLEDs. The variation of the emission spectrum is also evaluated as a function of temperature and applied potential, finding that emission redshifts by <3 nm under low temperature and by <0.3 nm V−1 with operating voltage. The prominent oxidation pathway of Sn is identified and this is suppressed with the aid of H3PO2. This strategy prevents the oxidation of the constituent precursors, through both its moderate reducing properties and through its forming complexes with the perovskite that increase the energetic barrier toward Sn oxidation. The H3PO2 additionally seeds crystal growth during film formation, improving film quality. PeLEDs are reported with an EQE of 0.3% and a brightness of 70 cd m−2; this is the record among reported red‐emitting, lead‐free PeLEDs. [ABSTRACT FROM AUTHOR]

For metal halide perovskite (MHP)‐based light‐emitting diodes (PeLEDs), effective radiative recombination of the injected holes and electrons within the MHP layer and minimized injection energy barriers at the interfaces between MHP emission layer and charge injection layers are prerequisites for high‐performance and stable PeLEDs. Herein, for the first time, novel p‐type carbon quantum dots (CQDs) are introduced as a hole injection layer in PeLEDs to replace acidic poly(3,4‐ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) layer. The CQDs demonstrate high hole transport mobility and desirable hole injection energy level. Moreover, the carboxyl, amine, and hydroxyl groups on CQDs not only offer a hydrophilic surface for high‐quality perovskite layer growth, but also passivate the perovskite surface defects to suppress the interfacial exciton quenching. Based on the multifunctional p‐type CQDs, high‐performance green CsPbBr3 PeLEDs with a low turn‐on voltage of only 2.8 V, maximum luminance of 25 770 cd m−2, and maximum external quantum efficiency (EQE) of 13.8% are achieved. The PeLEDs also show good operational stability and long‐term environmental stability. The first application of CQDs as a hole injection layer in PeLEDs breaks through the traditional cognition of carbon materials and opens up new pathways for the developments of carbon nanomaterials in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The development of ultrastable and low‐threshold random lasers has long been the subject of intense academic research, in anticipation for widespread applications spanning from military weapon devices, biomedical therapy, and materials processing to energy savings. Reported here is the first example of ultrastable and low‐threshold random lasing emissions ranging from blue to red based on narrow bandwidth emission triangular carbon quantum dots (CQDs). The lasing thresholds of the blue, green, and red random lasers are determined to be as low as 0.087, 0.052, and 0.048 mJ cm−2, and the corresponding narrow full widths at half maximum are 0.9, 0.37, and 0.82 nm, respectively. Furthermore, such random lasers demonstrate outstanding stability. This work will inspire further research on lasers operating in other modes, based on the CQDs, such as the whispering‐gallery mode and the Fabry–Pérot mode, which will expedite the development of the next‐generation of ultrastable and low‐threshold CQDs‐based laser technology. Ultrastable and low‐threshold random lasing emissions ranging from blue to red, based on narrow‐bandwidth‐emission triangular carbon quantum dots is reported. The lasing thresholds of the blue, green, and red random lasers are determined to be as low as 0.087, 0.052, and 0.048 mJ cm−2, respectively. [ABSTRACT FROM AUTHOR]

Perovskite quantum dots (QDs) are of interest for solution‐processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self‐assembly strategy that relies on sodiumd—an assembly director that passivates the surface of the QDs and induces self‐assembly to form ordered three‐dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self‐assembly and superlattice formation. Compared to conventional organic‐ligand‐passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron‐length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter‐dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red‐shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond‐sustained lasing with a threshold of 25 µJ cm–2. [ABSTRACT FROM AUTHOR]

Water-soluble and surface charge-tunable amine-functionalized polyhydroxylated fullerene nanoparticles with a strong green emission were synthesized by grinding and hydrothermal treatment. The quantum yield of the nanoparticles was as high as 17%, which is the highest value recorded for fluorescent fullerene materials. The amine-functionalized polyhydroxylated fullerene nanoparticles with high surface charge were found to easily penetrate into breast cancer cells, HeLa cells and cardiac progenitor stem cells, opening up great opportunities for their bio-medical applications. [ABSTRACT FROM AUTHOR]

The development of efficient red bandgap emission carbon quantum dots (CQDs) for realizing high‐performance electroluminescent warm white light‐emitting diodes (warm‐WLEDs) represents a grand challenge. Here, the synthesis of three red‐emissive electron‐donating group passivated CQDs (R‐EGP‐CQDs): R‐EGP‐CQDs‐NMe2, ‐NEt2, and ‐NPr2 is reported. The R‐EGP‐CQDs, well soluble in common organic solvents, display bright red bandgap emission at 637, 642, and 645 nm, respectively, reaching the highest photoluminescence quantum yield (QY) up to 86.0% in ethanol. Theoretical investigations reveal that the red bandgap emission originates from the rigid π‐conjugated skeleton structure, and the ‐NMe2, ‐NEt2, and ‐NPr2 passivation plays a key role in inducing charge transfer excited state in the π‐conjugated structure to afford the high QY. Solution‐processed electroluminescent warm‐WLEDs based on the R‐EGP‐CQDs‐NMe2, ‐NEt2, and ‐NPr2 display voltage‐stable warm white spectra with a maximum luminance of 5248–5909 cd m−2 and a current efficiency of 3.65–3.85 cd A−1. The warm‐WLEDs also show good long‐term operational stability (L/L0 > 80% after 50 h operation, L0: 1000 cd m−2). The electron‐donating group passivation strategy opens a new avenue to realizing efficient red bandgap emission CQDs and developing high‐performance electroluminescent warm‐WLEDs. [ABSTRACT FROM AUTHOR]

Inexpensive and highly luminescent Cu(I) complexes exhibit great potential as emitters in organic light‐emitting diodes (OLEDs), especially in white OLEDs (WOLEDs). In this work, two compounds 9‐(3‐(quinolin‐4‐yl)phenyl)‐9H‐carbazole (CzPQ) and 9,9′‐(quinoline‐4,6‐diylbis(3,1‐phenylene))bis(9H‐carbazole) (2CzPQ) are designed and synthesized to form Cu(I) complexes in situ by codeposition with copper iodide (CuI). The corresponding OLEDs show an orange red emission with a maximum external quantum efficiency (EQE) of 6.7%. Based on this result, an "on‐and‐off" strategy is proposed to achieve WOLEDs with the combination of Cu(I) complex layer and the pure ligand layer by controlling the shutter of CuI source on and off. The optimized WOLEDs give a maximum EQE of 2.4% with excellent Commission Internationale de L'Eclairage (CIE) coordinates of (0.32, 0.33) and a remarkable color‐rendering index (CRI) of 94. It can be forecasted that the device efficiency would be improved by tuning the chemical structure of the ligand. [ABSTRACT FROM AUTHOR]