Alternating layer addition approach to CdSe/CdS core/shell quantum dots with near-unity quantum yield and high on-time fractions

Greytak, Andrew B.; Allen, Peter M.; Liu, Wenhao; Zhao, Jing; Young, Elizabeth R.; Popović, Zoran V.; Walker, Brian; Nocera, Daniel G.; Bawendi, Moungi G.

doi:10.1039/c2sc00561a

Cited by 210 publications

(233 citation statements)

References 46 publications

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“…1.4 nm was carried out through a modified selective ion layer adsorption and reaction (SILAR) technique, as Greytak et al previously reported. 6,46 In this synthesis, CdSe cores were formed. Then, the CdS shell layers were grown around the cores at 180°C, which is not high enough for an alloying to occur.…”

Section: Methodsmentioning

confidence: 99%

Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging

et al. 2013

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In nanocrystal quantum dots (NQDs), generating multiexcitons offers an enabling tool for enhancing NQD-based devices. However, the photocharging effect makes understanding multiexciton kinetics in NQD solids fundamentally challenging, which is critically important for solid-state devices. To date, this lack of understanding and the spectralÀtemporal aspects of the multiexciton recombination still remain unresolved in solid NQD ensembles, which is mainly due to the confusion with recombination of carriers in charged NQDs. In this work, we reveal the spectralÀtemporal behavior of biexcitons (BXs) in the presence of photocharging using near-unity quantum yield CdSe/CdS NQDs exhibiting substantial suppression of Auger recombination. Here, recombinations of biexcitons and single excitons (Xs) are successfully resolved in the presence of trions in the ensemble measurements of time-correlated single-photon counting at variable excitation intensities and varying emission wavelengths. The spectral behaviors of BXs and Xs are obtained for three NQD samples with different core sizes, revealing the strength tunability of the XÀX interaction energy in these NQDs. The extraction of spectrally resolved X, BX, and trion kinetics, which are otherwise spectrally unresolved, is enabled by our approach introducing integrated time-resolved fluorescence. The results are further experimentally verified by cross-checking excitation intensity and exposure time dependencies as well as the temporal evolutions of the photoluminescence spectra, all of which prove to be consistent. The BX and X energies are also confirmed by theoretical calculations. These findings fill an important gap in understanding the spectral dynamics of multiexcitons in such NQD solids under the influence of photocharging effects, paving the way to engineering of multiexciton kinetics in nanocrystal optoelectronics, including NQD-based lasing, photovoltaics, and photodetection.

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Section: Methodsmentioning

confidence: 99%

Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging

et al. 2013

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“…For this purpose, the passivation of the surface of the QDs has been carefully studied in order to minimize the traps and to provide a barrier with the surrounding medium [27], and hence to provide an enhancement of the emission efficiency [28]. Indeed, colloidal nanocrystals are usually characterized by temperature-insensitive emission, because the barriers are so high that thermal energy losses are inhibited.…”

Section: Emission Of Lightmentioning

confidence: 99%

Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

Suárez¹

2016

Eur. Phys. J. Appl. Phys.

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Abstract. Semiconductor nanocrystals have arisen as outstanding materials to develop a new generation of optoelectronic devices. Their fabrication under simple and low cost colloidal chemistry methods results in cheap nanostructures able to provide a wide range of optical functionalities. Their attractive optical properties include a high absorption cross section below the band gap, a high quantum yield emission at room temperature, or the capability of tuning the band-gap with the size or the base material. In addition, their solution process nature enables an easy integration on several substrates and photonic structures. As a consequence, these nanoparticles have been extensively proposed to develop several photonic applications, such as detection of light, optical gain, generation of light or sensing. This manuscript reviews the great effort undertaken by the scientific community to construct active photonic devices based on these nanoparticles. The conditions to demonstrate stimulated emission are carefully studied by comparing the dependence of the optical properties of the nanocrystals with their size, shape and composition. In addition, this paper describes the design of different photonic architectures (waveguides and cavities) to enhance the generation of photoluminescence, and hence to reduce the threshold of optical gain. Finally, semiconductor nanocrystals are compared to organometallic halide perovskites, as this novel material has emerged as an alternative to colloidal nanoparticles.

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“…As a result of the confinement of the electron and hole inside the core region, higher oscillator strength and higher quantum yield can be obtained. 13 Recently, semiconductor nanocrystals having Type-I electronic structure have been synthesized with almost near-unity quantum yield, 14 and this makes them highly promising candidates for the next generation light-emitting diodes 15 and lasing applications. 16 In contrast to Type-I semiconductor nanocrystals, semiconductor nanocrystals having Type-II electronic structure, where there is a significantly reduced overlap between electron and hole wave functions, show different and interesting properties.…”

Section: ■ Introductionmentioning

confidence: 99%

Type-II Colloidal Quantum Wells: CdSe/CdTe Core/Crown Heteronanoplatelets

et al. 2015

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Solution-processed quantum wells, also known as colloidal nanoplatelets (NPLs), are emerging as promising materials for colloidal optoelectronics. In this work, we report the synthesis and characterization of CdSe/CdTe core/crown NPLs exhibiting a Type-II electronic structure and Type-II specific optical properties. Here, based on a core-seeded approach, the CdSe/CdTe core/crown NPLs were synthesized with well-controlled CdTe crown coatings. Uniform and epitaxial growth of CdTe crown region was verified by using structural characterization techniques including transmission electron microscopy (TEM) with quantitative EDX analysis and X-ray diffraction (XRD). Also the optical properties were systematically studied in these Type-II NPLs that reveal strongly red-shifted photoluminescence (up to ∼150 nm) along with 2 orders of magnitude longer fluorescence lifetimes (up to 190 ns) compared to the Type-I NPLs owing to spatially indirect excitons at the Type-II interface between the CdSe core and the CdTe crown regions. Photoluminescence excitation spectroscopy confirms that this strongly red-shifted emission actually arises from the CdSe/CdTe NPLs. In addition, temperature-dependent time-resolved fluorescence spectroscopy was performed to reveal the temperature-dependent fluorescence decay kinetics of the Type-II NPLs exhibiting interesting behavior. Also, water-soluble Type-II NPLs were achieved via ligand exchange of the CdSe/CdTe core/crown NPLs by using 3-mercaptopropionic acid (MPA), which allows for enhanced charge extraction efficiency owing to their shorter chain length and enables high quality film formation by layer-by-layer (LBL) assembly. With all of these appealing properties, the CdSe/CdTe core/crown heterostructures having Type-II electronic structure presented here are highly promising for light-harvesting applications.

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Alternating layer addition approach to CdSe/CdS core/shell quantum dots with near-unity quantum yield and high on-time fractions

Cited by 210 publications

References 46 publications

Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging

Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging

Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

Type-II Colloidal Quantum Wells: CdSe/CdTe Core/Crown Heteronanoplatelets

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