The Avogadro project has developed an advanced molecule editor and visualizer designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It offers flexible, high quality rendering, and a powerful plugin architecture. Typical uses include building molecular structures, formatting input files, and analyzing output of a wide variety of computational chemistry packages. By using the CML file format as its native document type, Avogadro seeks to enhance the semantic accessibility of chemical data types. The work presented here details the Avogadro library, which is a framework providing a code library and application programming interface (API) with three-dimensional visualization capabilities; and has direct applications to research and education in the fields of chemistry, physics, materials science, and biology. The Avogadro application provides a rich graphical interface using dynamically loaded plugins through the library itself. The application and library can each be extended by implementing a plugin module in C++ or Python to explore different visualization techniques, build/manipulate molecular structures, and interact with other programs. We describe some example extensions, one which uses a genetic algorithm to find stable crystal structures, and one which interfaces with the PackMol program to create packed, solvated structures for molecular dynamics simulations. The 1.0 release series of Avogadro is the main focus of the results discussed here. Avogadro offers a semantic chemical builder and platform for visualization and analysis. For users, it offers an easy-to-use builder, integrated support for downloading from common databases such as PubChem and the Protein Data Bank, extracting chemical data from a wide variety of formats, including computational chemistry output, and native, semantic support for the CML file format. For developers, it can be easily extended via a powerful plugin mechanism to support new features in organic chemistry, inorganic complexes, drug design, materials, biomolecules, and simulations. Avogadro is freely available under an open-source license from http://avogadro.openmolecules.net
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Avogadro: an advanced semantic chemical editor, visualization, and analysis platform

Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1–3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4–8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively—still well behind the performance of organic LEDs10–12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display. A strategy for managing the compositional distribution in metal halide perovskite light-emitting diodes enables them to surpass 20% external quantum efficiency—a step towards their practical application in lighting and displays.

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Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent

Novel quantum-dot light-emitting diodes based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals are reported. The well-dispersed, single-crystal quantum dots (QDs) exhibit high quantum yields, and tunable light emission wavelength. The demonstration of these novel perovskite QDs opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.

Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3)

This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.

Emergence of colloidal quantum-dot light-emitting technologies

Perovskite quantum wells yield highly efficient LEDs spanning the visible and near-infrared.

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Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells

Bright, efficient red, green and blue quantum-dot LEDs are realized by customizing the nanostructure of the quantum dots.

High-efficiency light-emitting devices based on quantum dots with tailored nanostructures

For the state-of-the-art quantum dot light-emitting diodes, while the ZnO nanoparticle layers can provide effective electron injections into quantum dots layers, the hole transporting materials usually cannot guarantee sufficient hole injection owing to the deep valence band of quantum dots. Developing proper hole transporting materials to match energy levels with quantum dots remains a great challenge to further improve the device efficiency and operation lifetime. Here we demonstrate high-performance quantum dot light-emitting diodes with much extended operation lifetime using quantum dots with tailored energy band structures that are favorable for hole injections. These devices show a T95 operation lifetime of more than 2300 h with an initial brightness of 1000 cd m−2, and an equivalent T50 lifetime at 100 cd m−2 of more than 2,200,000 h, which meets the industrial requirement for display applications. The commercialization of light-emitting diodes based on emissive quantum dots (e.g. QLEDs) is hindered by their inherent poor operational lifetime. Using an intelligent energy-level design strategy, Qian et al. demonstrate QLEDs with operational lifetime that meets industrial display standards.

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Highly stable QLEDs with improved hole injection via quantum dot structure tailoring

A family of π-extended platinum(II) porphyrins has been synthesized and incorporated into solution processed polymer light emitting diodes (PLEDs) and vapor deposited multilayer organic light emitting diodes (OLEDs), giving rise to devices with peak emission ranging from 771 to 1005 nm. The longest wavelength emitter, platinum(II)-5,10,15,20-(3,5-di-tert-butylphenyl)tetraanthroporphyrin (Pt-Ar4TAP), shows an emission maximum at 1005 nm, an external quantum efficiency (EQE) of 0.12%, and a maximum radiant emittance (Rmax) of 0.23 mW/cm2 in single layer PLED architectures, which is enhanced to an EQE of 0.20% with an Rmax of 0.57 mW/cm2 upon vapor deposition of an electron transport layer. In an effort to understand substituent effects and enhance the performance of π-extended Pt-porphyrins in PLEDs and OLEDs, a family of Pt-tetrabenzoporphyrins (Pt-TBPs) with varying functionality was investigated. The luminescent lifetimes of the Pt-TBPs in solution and in films were measured, and a strong correlation was...

Extended Conjugation Platinum(II) Porphyrins for use in Near-Infrared Emitting Organic Light Emitting Diodes

High-Efficient Deep-Blue Light-Emitting Diodes by Using High Quality ZnxCd1−xS/ZnS Core/Shell Quantum Dots

The operating lifetime of blue quantum-dot light-emitting diodes (QLED) is currently a short slab for this emerging display technology. To pinpoint the origin of device degradation, here we apply multiple techniques to monitor the electric-field distribution and space-charge accumulation across the multilayered structure before and after lifetime tests. Evident by charge-modulated electro-absorption and capacitance-voltage characteristics, the excited electrons in blue quantum dots (QD) are prone to cross the type II junction between the QD emission layer and the electron-transporting layer (ETL) due to the offset of conduction band minimum, leading to space-charge accumulation and operating-voltage rise in the ETL. Therefore, unlike those very stable red devices, of which the lifetime is primarily limited by the slow degradation of hole-transporting layer, the poor lifetime of blue QLED originates from the fast degradation at the QD-ETL junction. Materials engineering for efficient electron injection is prerequisite for the boost of operating lifetime. Wide application of quantum dot light emitting diodes (QLED) in display technology is hindered by the poor lifetime of the blue QLEDs. Here, the degradation mechanism is shown to originate from space charge accumulation in the electron-transporting layer enabling improvements in blue QLED lifetimes.

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Yang Yixing

Papers

High-efficiency light-emitting devices based on quantum dots with tailored nanostructures

Highly stable QLEDs with improved hole injection via quantum dot structure tailoring

Extended Conjugation Platinum(II) Porphyrins for use in Near-Infrared Emitting Organic Light Emitting Diodes

High-Efficient Deep-Blue Light-Emitting Diodes by Using High Quality ZnxCd1−xS/ZnS Core/Shell Quantum Dots

On the degradation mechanisms of quantum-dot light-emitting diodes