Search query: Colloidal quantum nanostructures: emerging materials for  display applications

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abstract: Abstract Colloidal semiconductor nanocrystals (SCNCs) or, more broadly, colloidal quantum nanostructures constitute outstanding model systems for investigating size and dimensionality effects. Their nanoscale dimensions lead to quantum confinement effects that enable tuning of their optical and electronic properties. Thus, emission color control with narrow photoluminescence spectra, wide absorbance spectra, and outstanding photostability, combined with their chemical processability through control of their surface chemistry leads to the emergence of SCNCs as outstanding materials for present and next generation displays. In this Review, we present the fundamental chemical and physical properties of SCNCs, followed by a description of the advantages of different colloidal quantum nanostructures for display applications. The open challenges with respect to their optical activity are addressed. Both photoluminescent and electroluminescent display scenarios utilizing SCNCs are described.
author_names: Yossef E Panfil

Meirav Oded

Uri Banin
title: Colloidal Quantum Nanostructures: Emerging Materials for Display Applications
venue: Angewandte Chemie
year: 2018

abstract: Professor Uri Banin holds the Alfred Erica Larisch Memorial Chair at the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem (HU) Banin obtained his PhD in Physical Chemistry (Magna Cum Laude, 1995) from the Hebrew University of Jerusalem and performed his postdoctoral research at the University of California at Berkeley (1994 97) He was the founding director of the HU Center for Nanoscience and Nanotechnology (2001 2010) and is a founder of Qlight Nanotech that developed colloidal quantum materials for display applications, and was acquired by Merck KGaA, Darmstadt, Germany. His research focuses on the chemistry and physics of nanocrystals including synthesis of nanoparticles, sizeand shape dependent properties, and emerging applications in displays, lighting, solar energy harvesting, 3D printing, electronics, and biology. Meirav Oded
author_names: Yossef E Panfil

Meirav Oded

Nir Waiskopf

Uri Banin
title: Material Challenges for Colloidal Quantum Nanostructures in Next Generation Displays
year: 2020

abstract: Colloidal quantum materials are nanocrystals containing hundreds to thousands of atoms that exhibit unique properties resulting from their small finite dimensions. The extraordinary flexibility in tuning their properties via composition, size and dimensionality related quantum confinement effects and surface engineering combined with their scalable bottom up manufacturing has already led to their commercialization in different light emitting applications, such as materials for displays and as fluorescent agents for imaging and sensing. Beyond light emission, harnessing absorbed light energy to perform useful chemical work is an important new avenue for diverse applications of the colloidal quantum materials. Here, we introduce the colloidal quantum materials and their virtues, focusing on the "all in one system" concept for semiconductor metal hybrid nanoparticles acting as photocatalysts. Next, their emerging photocatalytic functionalities are highlighted, including their action as photocatalysts for solar to fuel conversion and as photoinitiators for photo curing and biomedical applications, such as phototherapy, sterilization, and diagnostics.
author_names: Nir Waiskopf

Uri Banin
title: Colloidal Quantum Materials for Photocatalytic Applications
year: 2019

abstract: Abstract Metal halide perovskites have affirmed their pedigree as extraordinary semiconducting materials, exhibiting properties rivalling those observed in single crystal compound semiconductors. Perovskites show tremendous versatilities in both structure and composition tuning, and therefore applications ranging from optoelectronics to X ray imaging and spintronics, neuromorphic electronics are emerging. Moreover, when their dimensions become comparable to the exciton Bohr radius, perovskite nanostructures and layered systems display remarkable properties because of quantum confinement. Nanostructured and lower dimensional layered perovskites exhibit properties that are yet to be fully exploited such as extraordinarily high luminescence, narrow emissions, high exciton binding energies, strong non linear phenomena, and carrier cascade characteristics. This review, while highlighting the frontier phenomena that continue to be unravelled, outlines how confined structures of these materials have demonstrated properties that promise to unlock exceptional quantum phenomena to challenge the optoelectronic limits.
author_names: Sneha Avinash Kulkarni

Natalia Yantara

Kim Seng Tan

Nripan Mathews

Subodh Gautam Mhaisalkar
title: Perovskite nanostructures: Leveraging quantum effects to challenge optoelectronic limits
year: 2020

abstract: Semiconductor quantum nanostructures, such as 0D quantum dots (QDs) 1D nanorods and 2D nanoplatelets (NPLs) quantum rings (QRs) and quantum wells (QWs) exhibit unique quantum mechanical and optoelectronic properties due to spatial confinement of excitons in one or more dimensions ~10 9 m) They have received increasing research interest in recent years owing to their intriguing fundamental properties that can be leveraged for potential applications in optoelectronic and display devices as cost effective and quantum efficient luminophores. They have been successfully used to implement and design light emitting diodes (LEDs) lasers, photodetectors, solar cells, biomedical imagers, etc. This is owing to their morphological bandgap tunability, fast fluorescence lifetime and unique optical characteristics supporting tunable pure color or wide spectral emission. Among the wide range of available and newly studied semiconductor quantum nanostructures, firstly (i) NPLs and QRs of II VI materials and alloys thereof, and secondly (ii) QDs and QWs of III V dilute nitride/bismide alloy materials are two families of nanostructures that have emerged as very promising candidates for novel semiconductor device and optoelectronic applications. In this thesis, we report studies on the aforementioned two families of semiconductor quantum nanostructures. The first part of the thesis focuses on the study of II VI (CdSe and CdS) NPLs and optoelectronic properties thereof under varying physical conditions such as geometrical dimensions, temperature, material composition, topology and optical polarization. NPLs are a unique class of atomically flat quasi 2D quantum confined nanocrystals, often synthesized using wide bandgap II VI materials, having well defined thicknesses of several monolayers (MLs) Their sizes enable them to be colloidally suspended in solution. Recent advancements in colloidal chemistry has led to the efficient synthesis of high quality single crystal NPL samples having reduced nonradiative recombination paths and enhanced optical properties. They exhibit strong 1D confinement as their thickness is very
author_names: Sumanta Bose
title: Semiconductor quantum nanostructures for optoelectronic applications
year: 2018

abstract: In recent years, lead halide perovskites have not only proven to be a promising material for solar cell applications, but they have also shown a huge potential for light emitting devices and other optoelectronic applications. Most of the initial studies focused on bulk perovskite materials. However, emerging colloidal perovskite nanocrystals have been shown to exhibit superior qualities relating to their efficiency and functionality. On the nanoscale, size dependent effects can be exploited to tune the nanocrystals' properties. In the present work, two dimensional perovskite nanoplatelets and quasi two dimensional layered hybrid perovskites are investigated. A new and systematic variation of the ligand concentration during the nanocrystal synthesis is presented. This enables the fabrication of colloidal two dimensional methylammonium lead bromide perovskite nanoplatelets of varying thicknesses down to only a single unit cell. Photoluminescence and absorption spectra show the appearance of clear excitonic features in the thinnest structures and a blue shift in the emission wavelength of more than 90 nm in comparison to the bulk counterpart. Additionally, in the thinnest structures the exciton binding energy increases up to several hundreds of meV due to a reduced excitonic screening. For the first time the quantum size effect in these nanoplatelets is quantitatively described through model calculations. Miniband formation in the multilayer structures lowers the emission energy with respect to the isolated nanoplatelet. Thickness dependent photoluminescence lifetime measurements are performed. The recorded lifetimes decrease with thinner nanoplatelets as the exciton binding energy increases. Temperature dependent photoluminescence measurements on cesium lead bromide perovskite nanoplatelets are carried out. A theoretical model considering acoustic and optical phonons as the main sources for scattering of excitons, shows that the former dominate at temperatures below 90 K and the latter above this temperature. Interestingly, temperature dependent time resolved photoluminescence measurements display contributions of bright and dark excitons to the decay curves below 60 K. At higher temperatures an antiquenching behavior of the luminescence is observed, indicating that ligands play an important role in these structures with a high surface to volume ratio. The interlayer distance in layered hybrid perovskites is systematically varied to investigate its impact on structure function relationships and electronic coupling between the perovskite layers. It is found that the optical bandgap is determined mainly by two parameters. First, the length of the organic ligands separating the inorganic perovskite sheets influences the tilt angle of the perovskite octahedra. An increase of the optical bandgap with larger tilt angles is observed. Secondly, electronic coupling between the perovskite sheets constituting the multilayer structures is found to have an impact on the bandgap, albeit significantly smaller than the effect induced by the change in tilt angles. Importantly, the electronic coupling only occurs for perovskite multilayers with an interlayer distance below 1.5 nm. This thesis contributes to a fundamental understanding of optical properties of two dimensional perovskites. It focuses on thickness dependent quantum size effects, exciton phonon interactions, and structure function relationships.
author_names: Jasmina A Sichert
title: Quantum size effects and carrier dynamics in two dimensional lead halide perovskite nanostructures
year: 2019

abstract: Metal lead halide perovskite nanocrystals have emerged as promising candidates for optoelectronic applications. However, the inclusion of toxic lead is a major concern for the commercial viability of these materials. Herein, we introduce a new family of non toxic reduced dimension Rb2CuX3 (X Br, Cl) colloidal nanocrystals with one dimensional crystal structure consisting [CuX4]3 ribbons isolated by Rb+ cations. These nanocrystals were synthesised using a room temperature method under ambient conditions, which makes them cost effective and scalable. Phase purity quantification was confirmed by Rietveld refinement of powder X ray diffraction and corroborated by 87Rb MAS NMR technique. Both samples also exhibited high thermal stability up to 500 degC, which is essential for optoelectronic applications. Rb2CuBr3 and Rb2CuCl3 display PL emission peaks at 387 nm and 400 nm with high PLQYs of ~100% and ~49% respectively. Lastly, the first colloidal synthesis of quantum confined rubidium copper halide based nanocrystals opens up a new avenue to exploit their optical properties in lighting technology as well as water sterilisation and air purification.
author_names: Parth Vashishtha

Thomas J N Hooper

Yanan Fang

Deviana Kathleen

David Giovanni

Maciej Klein

Tze Chien Sum

Subodh Gautam Mhaisalkar

Nripan Mathews

Tim White
title: Room temperature synthesis of low dimensional rubidium copper halide colloidal nanocrystals with near unity photoluminescence quantum yield.
venue: Nanoscale
year: 2020

abstract: Tunable, narrow linewidth photoluminescence with nearly ideal quantum yields and solution processability make colloidal quantum dots (QDs) a unique class of emitters for a variety of applications including light emitting diodes (LEDs) Wide color gamut and high color saturation that can be achieved with QDs along with recent advances in QD LEDs motivate their use as large area, patternable electroluminescent materials especially in displays. In this review, critical issues in performance and long term stability of QD LEDs, Cd free compositions necessary for practical applications, lower symmetry heterostructures that impart new capabilities, and unconventional fabrication approaches are discussed. As the current CdSe based QD LEDs approach their performance limits, emerging nanorod heterostructures, as exemplified by the double heterojunction nanorods (DHNRs) can extend efficiencies beyond these limits. Furthermore, enhancements in device lifetime and light detection/photovoltaic capabilities using the same high performance DHNR LEDs can allow exciting prospects for novel emissive displays. Such multifunctional LEDs that can be solution processed into large area, mulitcolor pixel arrays may fundamentally alter how we perceive, interact with and utilize display devices.
author_names: Yiran Jiang

Seong-Yong Cho

Moonsub Shim
title: Light emitting diodes of colloidal quantum dots and nanorod heterostructures for future emissive displays
year: 2018

abstract: Investigation of carrier transport and electronic properties of highly crosslinked ligand exchanged colloidal quantum dot (QD) assemblies (Fig. 1a b) is vital for the utilization of these class of materials in diverse emerging practical applications. So far, their tunability of energy bandgap and the discrete energy levels formation have attracted great interest in their applications in many devices where optical properties are primarily important (e.g. photovoltaics, displays [QLEDs] and even laser) On the other hand, QD assemblies are prospective for thermoelectric applications, since low dimensionality leads to enhanced Seebeck effect and suppressed thermal conductivity. 3 4 For those applications, some certain doping levels are required; thus knowledge on how many electrons can sit for each QD discrete energy levels is vital. To understand electronic state degeneracy in QD system is challenging since it will be strongly influenced by the energetic landscape of the quantum confinement, in addition to the compound type. So far, it is still too difficult to elucidate degeneracy information only from the optical characterization of the QD assemblies. Here we demonstrate the probing of the electronic state degeneracy of QD assemblies via measurement of electronic transport. High carrier density accumulation in electric double layer transistor (EDLT) of PbS QD, which was gated using ionic liquid, enables us to attain sheet carrier density in the order of 10 cm. In addition to be able to fill almost all of the charge carrier traps in the quantum dot film and make it highly conducting, the high carrier density accumulation is virtually sufficient to greatly control the Fermi level beyond quantum dots` HOMO LUMO, thus accessing the discrete energy levels to fill them. The observation of negative transconductance and conductivity peaks of the EDLT at some certain carrier density value is attributed to the half filling of the discrete energy band of the QDs. From the correlation of the carrier density and QD density in the assembly, the number of accumulated electrons per individual QD can be counted to obtain the numbers of electronic state degeneracy for each discrete energy levels. For PbS QD, as (Fig. 1d) the number of the degeneracy can be approached by both the number of the degeneracy of its bulk material at the conduction minima and the quasi hydrogen model that is used to describe the energetic landscape of a QD. Through this probing, we can know how much dopant is necessary to dope the QDs up to some certain levels required for many applications and to formulate various doping strategies. Refs: [1] M. Kovalenko, ACS Nano 9, 1012 (2015) [2] A. Nurmikko,Nature Nano. 10, 1001 (2015) [3] J. Urban, Nature Nano. 10, 997 (2015) [4] Jpn. Pat. Appl. JP2016 137453; [5] S.Z. Bisri, et al. Adv. Mater. 25, 4309 (2013) Adv. Mater. 26, 5639 (2014) Figure 1 (a) Schematic diagram on the assembly of PbS QD to form superlattice assembly by crosslinking them with shorter ligands and (b) its HAADF scanning TEM (inset: TEM of individual QD in atomic detail) (c) Application of ionic liquid gating is able to accumulate very high carrier density and tune QD assembly Fermi energy, (d) the ID VG transfer characteristics of PbS QDs shows negative transconductance that indicates the filling of the discrete energy levels. Di 65Hui Ying Yong Wu Li Xue Hui Chun Ji Xue Shu Jiang Yan Hui Jiang Yan Yu Gao Ji (2018 Zao Dao Tian Da Xue Xi Zao Dao Tian kiyanpasu) 17p F210 3
author_names: Satria Zulkarnaen Bisri

Maria Ibanez

Maksym V Kovalenko

Yoshihiro Iwasa
title: Probing Degeneracy of Discrete Electronic States of Colloidal Quantum Dots
year: 2018

abstract: Colloidal semiconductor nanocrystals, also known as "quantum dots" (QDs) represent an example of a disruptive technology for display and lighting applications. Their high luminescence efficiency and tunable, narrow emission are nearly ideal for achieving saturated colors and enriching the display or TV color gamut. Our contribution will discuss the next generation of inorganic nanostructures with electronic structure optimized for achieving emission characteristics beyond traditional near spherical QDs. For example, nano heterostructures with spherical CdSe QDs epitaxially integrated into CdS quantum rods combine high luminescence efficiency with giant extinction coefficients, large Stokes shifts, and linearly polarized emission. Such a set of characteristics can be ideal for LCD backlighting. The other class of emitters includes colloidal quantum wells (QWs) whose ensemble luminescence is significantly narrower than emission spectra of the best QD samples. Moreover, we show that colloidal QWs produce amplified spontaneous emission (ASE) with pump fluence thresholds as low as 6 mJ/cm2 and gain as high as 600 cm 1, on par with the best values for any solution processed material.
author_names: Chunxing She

Igor Fedin

Michael A Boles

Dmitriy S Dolzhnikov

Richard D Schaller

Matthew Pelton

Dmitri V Talapin
title: 12.2: Invited Paper: Colloidal Quantum Rods and Wells for Lighting and Lasing Applications
year: 2014