Lighting accounts for one-fifth of global electricity consumption1. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties2,3; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl6 octahedron in the excited state. By alloying sodium cations into Cs2AgInCl6, we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor4. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs2AgInCl6. The optimally alloyed Cs2(Ag0.60Na0.40)InCl6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies. After alloying with metal cations, a lead-free halide double perovskite shows stable performance and remarkably efficient white-light emission, with possible applications in lighting and display technologies.

Efficient and stable emission of warm-white light from lead-free halide double perovskites

Metal halide perovskites represent a flourishing area of research, driven by both their potential application in photo-voltaics and optoelectronics, and for the fundamental science underpinning their unique optoelectronic properties. The advent of colloidal methods for the synthesis of halide perovskite nanocrystals has brought to the attention inter-esting aspects of this new type of materials, above all their defect-tolerance. This review aims to provide an updated survey of this fast-moving field, with a main focus on their colloidal synthesis. We examine the chemistry and the ca-pability of different colloidal synthetic routes to control the shape, size and optical properties of the resulting nano-crystals. We also provide an up to date overview of their post-synthesis transformations, and summarize the various so-lution processes aimed at fabricating halide perovskite-based nanocomposites. We then review the fundamental optical properties of halide perovskite nanocrystals, by focusing on their linear optical properties, on the effects of quantum confinement and, then, on the current knowledge of their exciton binding energies. We also discuss the emergence of non-linear phenomena such as multiphoton absorption, biexcitons and carrier multiplication. At last, we provide an outlook in the field, with the most cogent open questions and possible future directions.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications and Their Optical Properties

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we...

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties.

Carbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications on account of carbon’s intrinsic merits of high stability, low cost, and environment-friendliness. However, the CQDs usually give broad emission with full width at half maximum exceeding 80 nm, which fundamentally limit their display applications. Here we demonstrate multicolored narrow bandwidth emission (full width at half maximum of 30 nm) from triangular CQDs with a quantum yield up to 54–72%. Detailed structural and optical characterizations together with theoretical calculations reveal that the molecular purity and crystalline perfection of the triangular CQDs are key to the high color-purity. Moreover, multicolored light-emitting diodes based on these CQDs display good stability, high color-purity, and high-performance with maximum luminance of 1882–4762 cd m−2 and current efficiency of 1.22–5.11 cd A−1. This work will set the stage for developing next-generation high-performance CQDs-based light-emitting diodes.

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Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs

Hybrid perovskites are currently one of the most active fields of research owing to their enormous potential for photovoltaics. The performance of 3D hybrid organic–inorganic perovskite solar cells has increased at an incredible rate, reaching power conversion efficiencies comparable to those of many established technologies. However, the commercial application of 3D hybrid perovskites is inhibited by their poor stability. Relative to 3D hybrid perovskites, low-dimensional — that is, 2D — hybrid perovskites have demonstrated higher moisture stability, offering new approaches to stabilizing perovskite-based photovoltaic devices. Furthermore, 2D hybrid perovskites have versatile structures, enabling the fine-tuning of their optoelectronic properties through compositional engineering. In this Review, we discuss the state of the art in 2D perovskites, providing an overview of structural and materials engineering aspects and optical and photophysical properties. Moreover, we discuss recent developments along with the main limitations of 3D perovskites and assess the advantages of 2D perovskites over their 3D parent structures in terms of stability. Finally, we review recent achievements in combining 3D and 2D perovskites as an approach to simultaneously boost device efficiency and stability, paving the way for mixed-dimensional perovskite solar cells for commercial applications. Combining low-dimensional and 3D perovskites is a promising approach to achieve stable and efficient solar cells. In this Review, we discuss the structural, optical and photophysical properties of low-dimensional perovskites, compare the stability and efficiency of 2D and 3D perovskite devices, and consider 2D/3D composites as a strategy to increase the stability of perovskite solar cells.

Dimensional tailoring of hybrid perovskites for photovoltaics

Organic-inorganic hybrid metal halide perovskites, an emerging class of solution processable photoactive materials, welcome a new member with a one-dimensional structure. Herein we report the synthesis, crystal structure and photophysical properties of one-dimensional organic lead bromide perovskites, C4N2H14PbBr4, in which the edge sharing octahedral lead bromide chains [PbBr4 2−]∞ are surrounded by the organic cations C4N2H14 2+ to form the bulk assembly of core-shell quantum wires. This unique one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient bluish white-light emissions with photoluminescence quantum efficiencies of approximately 20% for the bulk single crystals and 12% for the microscale crystals. This work verifies once again that one-dimensional systems are favourable for exciton self-trapping to produce highly efficient below-gap broadband luminescence, and opens up a new route towards superior light emitters based on bulk quantum materials. Low-dimensional systems exhibit unique optical properties. Yuanet al. demonstrate one-dimensional organic-inorganic hybrid metal halide perovskites with highly efficient bluish white-light emission due to efficient exciton self-trapping in the quantum-confined structure.

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Joshua Messier

Papers

One-dimensional organic lead halide perovskites with efficient bluish white-light emission.

A Microscale Perovskite as Single Component Broadband Phosphor for Downconversion White‐Light‐Emitting Devices