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Yasser Hassan

Bio: Yasser Hassan is an academic researcher from University of Oxford. The author has contributed to research in topics: Perovskite (structure) & Halide. The author has an hindex of 8, co-authored 13 publications receiving 530 citations. Previous affiliations of Yasser Hassan include Zagazig University & University of Toronto.

Papers
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Journal ArticleDOI
04 Mar 2021-Nature
TL;DR: This work exemplifies how the functionality of metal halide perovskites is extremely sensitive to the nature of the (nano)crystalline surface and presents a route through which to control the formation and migration of surface defects to achieve bandgap stability for light emission and could also have a broader impact on other optoelectronic applications-such as photovoltaics-for which band gap stability is required.
Abstract: Lead halide perovskites are promising semiconductors for light-emitting applications because they exhibit bright, bandgap-tunable luminescence with high colour purity1,2. Photoluminescence quantum yields close to unity have been achieved for perovskite nanocrystals across a broad range of emission colours, and light-emitting diodes with external quantum efficiencies exceeding 20 per cent-approaching those of commercial organic light-emitting diodes-have been demonstrated in both the infrared and the green emission channels1,3,4. However, owing to the formation of lower-bandgap iodide-rich domains, efficient and colour-stable red electroluminescence from mixed-halide perovskites has not yet been realized5,6. Here we report the treatment of mixed-halide perovskite nanocrystals with multidentate ligands to suppress halide segregation under electroluminescent operation. We demonstrate colour-stable, red emission centred at 620 nanometres, with an electroluminescence external quantum efficiency of 20.3 per cent. We show that a key function of the ligand treatment is to 'clean' the nanocrystal surface through the removal of lead atoms. Density functional theory calculations reveal that the binding between the ligands and the nanocrystal surface suppresses the formation of iodine Frenkel defects, which in turn inhibits halide segregation. Our work exemplifies how the functionality of metal halide perovskites is extremely sensitive to the nature of the (nano)crystalline surface and presents a route through which to control the formation and migration of surface defects. This is critical to achieve bandgap stability for light emission and could also have a broader impact on other optoelectronic applications-such as photovoltaics-for which bandgap stability is required.

353 citations

Journal ArticleDOI
TL;DR: Colloidally stable suspensions of lead halide perovskite nanocrystals are prepared from high-quality lead Halide nanocrystal seeds that are well suited for investigations of the intrinsic photophysics and spectroscopy of organic-inorganic metal halideperovskites.
Abstract: Colloidally stable suspensions of lead halide perovskite nanocrystals are prepared from high-quality lead halide nanocrystal seeds. Perovskite nanocrystals with different layered crystal structures are reported. These systems are well suited for investigations of the intrinsic photophysics and spectroscopy of organic-inorganic metal halide perovskites.

215 citations

Journal ArticleDOI
TL;DR: Two-dimensional electronic spectroscopy is used to measure the decoherence time of a superposition of the two lowest-energy excitons in colloidal CdSe nanocrystals in solution at room temperature and explores the effects of inhomogeneous broadening and the spectroscopic signatures of biexcitons.
Abstract: Coherent superpositions among eigenstates are of interest in fields as diverse as photosynthesis and quantum computation. In this report, we used two-dimensional electronic spectroscopy (2D ES) to measure the decoherence time of a superposition of the two lowest-energy excitons in colloidal CdSe nanocrystals (cubic phase) in solution at room temperature. In the electron–hole representation, the quantum coherence is, remarkably, a twelve-particle correlation. By comparing the measured 2D ES to simulations, we also explored the effects of inhomogeneous broadening and examined the spectroscopic signatures of biexcitons.

100 citations

Journal ArticleDOI
TL;DR: The preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide perovskite nanocrystals, where a solution of CH3NH3PbI3 nanocry crystals with a photoluminescence quantum yield exceeding 93% and tunable emission between 660 and 705 nm is obtained.
Abstract: Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for color tunable and high luminescence efficiency. While recent advances in perovskite-based light emitting diodes have resulted in external quantum efficiencies exceeding 12.4% for the green emitters, and infrared emitters based on 3D/2D mixed dimensional perovskites have exceeded 20%, the external quantum efficiencies of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitters with the desirable emission band gap to achieve full-color displays and white LEDs. Herein, we report the preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide (CH3NH3PbI3) perovskite nanocrystals, where we synthesize the nanocrystals via a ligand-assisted reprecipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions and toluene as the ...

98 citations

Journal ArticleDOI
TL;DR: Poly(styrene-b-4-vinylpyridine) (PS404b-P4VP76, where the subscripts refer to the number-averaged degree of polymerization) forms spherical crew-cut micelles with a PS core and a P4VP corona when...
Abstract: Poly(styrene-b-4-vinylpyridine) (PS404-b-P4VP76, where the subscripts refer to the number-averaged degree of polymerization) forms spherical crew-cut micelles with a PS core and a P4VP corona when ...

59 citations


Cited by
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01 Jun 2005

3,154 citations

Journal ArticleDOI
07 Oct 2016-Science
TL;DR: N nanoscale phase stabilization of CsPbI3 quantum dots (QDs) to low temperatures that can be used as the active component of efficient optoelectronic devices and describe the formation of α-CsP bI3 QD films that are phase-stable for months in ambient air.
Abstract: We show nanoscale phase stabilization of CsPbI 3 quantum dots (QDs) to low temperatures that can be used as the active component of efficient optoelectronic devices. CsPbI 3 is an all-inorganic analog to the hybrid organic cation halide perovskites, but the cubic phase of bulk CsPbI 3 (α-CsPbI 3 )—the variant with desirable band gap—is only stable at high temperatures. We describe the formation of α-CsPbI 3 QD films that are phase-stable for months in ambient air. The films exhibit long-range electronic transport and were used to fabricate colloidal perovskite QD photovoltaic cells with an open-circuit voltage of 1.23 volts and efficiency of 10.77%. These devices also function as light-emitting diodes with low turn-on voltage and tunable emission.

2,103 citations

Journal ArticleDOI
TL;DR: Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-EMitting diodes accomplished in two decades.
Abstract: Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices.

1,138 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide an updated survey of the field of halide perovskite nanocomposite colloidal synthesis, with a main focus on their colloidal synthetic routes to control shape, size and optical properties of the resulting nano-crystals.
Abstract: 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.

836 citations

Journal ArticleDOI
TL;DR: 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 and on the fundamental optical properties of halide perovskite nanocrystals.
Abstract: 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...

832 citations