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Perovskite nanocrystals (PeNCs) deliver size‐ and composition‐tunable luminescence of high efficiency and color purity in the visible range. However, attaining efficient electroluminescence (EL) in the near‐infrared (NIR) region from PeNCs is challenging, limiting their potential applications. Here we demonstrate a highly efficient NIR light‐emitting diode (LED) by doping ytterbium ions into a PeNCs host (Yb3+ : PeNCs), extending the EL wavelengths toward 1000 nm, which is achieved through a direct sensitization of Yb3+ ions by the PeNC host. Efficient quantum‐cutting processes enable high photoluminescence quantum yields (PLQYs) of up to 126 % from the Yb3+ : PeNCs. Through halide‐composition engineering and surface passivation to improve both PLQY and charge‐transport balance, we demonstrate an efficient NIR LED with a peak external quantum efficiency of 7.7 % at a central wavelength of 990 nm, representing the most efficient perovskite‐based LEDs with emission wavelengths beyond 850 nm. [ABSTRACT FROM AUTHOR]

Quasi‐2D perovskites show great promise for light‐emitting diodes owing to suppressed non‐radiative losses enabled by the energy funneling/cascading nanostructures. However, for red emission quasi‐2D perovskites, these ideal energy landscapes for efficient perovskite light‐emitting diodes (PeLEDs) can rarely be achieved due to detrimental aggregation of the low‐dimensional ligands in perovskite precursors, leading to poor device efficiency and stability. Here, a ligand‐modulated dimensionality control strategy is explored to achieve uniform phase distribution and reduce defect density for efficient light emission. In contrast to the model phenethylammonium iodide 2D ligand, the formation of small‐n phases can be inhibited by a structurally similar phenoxyethylammonium iodide ligand owing to the weakened aromatic stacking between ligands. Besides, the oxygen atoms can interact with the uncoordinated Pb2+ ions and promote the NI coordination in the perovskites, which greatly reduces the non‐radiative recombination defects in the ionic lattice. With this simple and effective approach, deep‐red quasi‐2D PeLEDs with record‐high external quantum efficiency of 21.6% and decent operational stability are achieved without the need for additional additives. These results highlight the potential of ligand‐modulated dimensionality control to achieve highly efficient and stable PeLEDs with a facile fabrication process. [ABSTRACT FROM AUTHOR]

Quantum dot light-emitting diodes (QLEDs) are a class of high-performance solution-processed electroluminescent (EL) devices highly attractive for next-generation display applications. Despite the encouraging advances in the mechanism investigation, material chemistry, and device engineering of QLEDs, the lack of standard protocols for the characterization of QLEDs may cause inaccurate measurements of device parameters and invalid comparison of different devices. Here, we report a comprehensive study on the characterizations of QLEDs using various methods. We show that the emission non-uniformity across the active area, non-Lambertian angular distributions of EL intensity, and discrepancies in the adopted spectral luminous efficiency functions could introduce significant errors in the device efficiency. Larger errors in the operational-lifetime measurements may arise from the inaccurate determination of the initial luminance and inconsistent methods for analyzing the luminance-decay curves. Finally, we suggest a set of recommended practices and a checklist for device characterizations, aiming to help the researchers in the QLED field to achieve accurate and reliable measurements. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) are a promising class of materials for next‐generation display and lighting applications. Since the first demonstration of bright electroluminescence (EL) from perovskite light‐emitting diodes (PeLEDs) in 2014, the EQEs of these devices increased from below 1% to more than 20% in merely four years. Despite the meteoritic rise of device efficiencies that placed the new LED technology in the spotlight, many scientific and technical challenges remain, preventing PeLEDs from advancing further into practical applications. The success of inorganic III‐V LEDs, or commercial LED technologies in general, lies in the ability to demonstrate the reliable generation of blue EL. For PeLEDs, high operational stability and efficient blue EL remain to be some of the most pressing goals. To accelerate further developments in these areas, the recent progress in the research of PeLEDs is reviewed. The authors attempt to establish preliminary connections between the degradation mechanisms and the strategies for improvements, exemplified by a selection of recent representative works in the field. Lessons learned from organic LEDs and perovskite solar cells point toward some of the most important directions. This progress report serves as a catalyst for further interdisciplinary research involving materials scientists, chemists, and physicists working together to realize operationally stable PeLEDs. [ABSTRACT FROM AUTHOR]

Reducing environmental impact is a key challenge for perovskite optoelectronics, as most high-performance devices are based on potentially toxic lead-halide perovskites. For photovoltaic solar cells, tin-lead (Sn–Pb) perovskite materials provide a promising solution for reducing toxicity. However, Sn–Pb perovskites typically exhibit low luminescence efficiencies, and are not ideal for light-emitting applications. Here we demonstrate highly luminescent germanium-lead (Ge–Pb) perovskite films with photoluminescence quantum efficiencies (PLQEs) of up to ~71%, showing a considerable relative improvement of ~34% over similarly prepared Ge-free, Pb-based perovskite films. In our initial demonstration of Ge–Pb perovskite LEDs, we achieve external quantum efficiencies (EQEs) of up to ~13.1% at high brightness (~1900 cd m−2), a step forward for reduced-toxicity perovskite LEDs. Our findings offer a new solution for developing eco-friendly light-emitting technologies based on perovskite semiconductors. Lead toxicity poses a big hurdle for the commercialization of perovskite optoelectronics, hence reducing the environmental impact holds the answer for its future application. To tackle this challenge, the authors utilize germanium to reduce the lead content, enabling highly luminescent eco-friendly compound for LEDs. [ABSTRACT FROM AUTHOR]

Electroluminescence of colloidal nanocrystals promises a new generation of high-performance and solution-processable light-emitting diodes. The operation of nanocrystal-based light-emitting diodes relies on the radiative recombination of electrically generated excitons. However, a fundamental question—how excitons are electrically generated in individual nanocrystals—remains unanswered. Here, we reveal a nanoscopic mechanism of sequential electron-hole injection for exciton generation in nanocrystal-based electroluminescent devices. To decipher the corresponding elementary processes, we develop electrically-pumped single-nanocrystal spectroscopy. While hole injection into neutral quantum dots is generally considered to be inefficient, we find that the intermediate negatively charged state of quantum dots triggers confinement-enhanced Coulomb interactions, which simultaneously accelerate hole injection and hinder excessive electron injection. In-situ/operando spectroscopy on state-of-the-art quantum-dot light-emitting diodes demonstrates that exciton generation at the ensemble level is consistent with the charge-confinement-enhanced sequential electron-hole injection mechanism probed at the single-nanocrystal level. Our findings provide a universal mechanism for enhancing charge balance in nanocrystal-based electroluminescent devices. Today it remains unclear how excitons are electrically generated in individual nanocrystals. Here, the authors propose the identification of the longlived intermediate QD– state for exciton generation of CdSe-based QD-LEDs by a room temperature electrically-pumped single-molecule spectroscopy. [ABSTRACT FROM AUTHOR]

Silicon nanocrystals have shown attractive properties for photonic and photovoltaic applications. We demonstrate all-Si light-emitting diodes based on boron-doped Si nanocrystal/c-Si p-n heterojunction structure, which show electroluminescence in the visible/infrared regions. The electroluminescence spectra of these diodes can be modified by changing the quantum confining barriers from SiO2 to Si3N4. Our results are an important demonstration of electroluminescence from boron-doped Si nanocrystals-a wide band gap absorber material for third generation photovoltaics. [ABSTRACT FROM AUTHOR]