Hybrid <i>N</i>-Butylamine-Based Ligands for Switching the Colloidal Solubility and Regimentation of Inorganic-Capped Nanocrystals

Sayevich, Vladimir; Guhrenz, Chris; Dzhagan, Volodymyr; Sin, Maria; Werheid, Matthias; Cai, Bin; Borchardt, Lars; Widmer, Johannes; Brunner, Eike; Lesnyak, Vladimir; Gaponik, Nikolai; Eychmüller, Alexander

doi:10.1021/acsnano.6b06996

Cited by 50 publications

(61 citation statements)

References 65 publications

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“…Here, ligand exchanges are performed at room temperature through the introduction of oleylamine (OLAm) and metal halides dissolved in methanol into a solution of NPLs in toluene. In contrast to the optical features of spherical NCs, 33,34 the exchange leads to a significant redshift of the optical features (approximately 80 meV for 4 ML NPLs) (see figure 1e and 1f). The introduction of the ligands (CdBr 2 and OLAm, denoted hereafter as Br-OLAm) leads to a fast loss of photoluminescence with the appearance of a broad red tail in the absorption spectrum.…”

Section: Resultsmentioning

confidence: 91%

Halide Ligands To Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness

et al. 2019

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Zinc blende II-VI semiconductor nanoplatelets (NPLs) are defined at the atomic scale along the thickness of the nanoparticle and are initially capped with carboxylates on the top and bottom [001] facets. These ligands are exchanged on CdSe NPLs with halides that act as X-L-type ligands. These CdSe NPLs are costabilized by amines to provide colloidal stability in nonpolar solvents. The hydrogen from the amine can participate in a hydrogen bond with the lone pair electrons of surface halides. After ligand exchange, the optical features are redshifted. Thus, ligand tuning is another way, in addition to confinement, to tune the optical features of NPLs. The improved surface passivation leads to an increase in the fluorescence quantum efficiency of up to 70% in the case of bromide. However, for chloride and iodide, the surface coverage is incomplete, and thus, the fluorescence quantum efficiency is lower. This ligand exchange is associated with a decrease in stress that leads to unfolding of the NPLs, which is particularly noticeable for iodide-capped NPLs.

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Section: Resultsmentioning

confidence: 91%

Halide Ligands To Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness

et al. 2019

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“…This does not however constitute direct evidence of Z-type binding; for instance, the presence of the metal in elemental analysis can be explained as X-type binding of the anion to Cd with the metal cation providing charge compensation, i.e., a bound ion pair. 24 , 53 We can, however, present several counter-arguments against X-type binding being the cause of near-unity PL QY.…”

Section: Resultsmentioning

confidence: 94%

Finding and Fixing Traps in II–VI and III–V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation

et al. 2018

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Energy levels in the band gap arising from surface states can dominate the optical and electronic properties of semiconductor nanocrystal quantum dots (QDs). Recent theoretical work has predicted that such trap states in II–VI and III–V QDs arise only from two-coordinated anions on the QD surface, offering the hypothesis that Lewis acid (Z-type) ligands should be able to completely passivate these anionic trap states. In this work, we provide experimental support for this hypothesis by demonstrating that Z-type ligation is the primary cause of PL QY increase when passivating undercoordinated CdTe QDs with various metal salts. Optimized treatments with InCl3 or CdCl2 afford a near-unity (>90%) photoluminescence quantum yield (PL QY), whereas other metal halogen or carboxylate salts provide a smaller increase in PL QY as a result of weaker binding or steric repulsion. The addition of non-Lewis acidic ligands (amines, alkylammonium chlorides) systematically gives a much smaller but non-negligible increase in the PL QY. We discuss possible reasons for this result, which points toward a more complex and dynamic QD surface. Finally we show that Z-type metal halide ligand treatments also lead to a strong increase in the PL QY of CdSe, CdS, and InP QDs and can increase the efficiency of sintered CdTe solar cells. These results show that surface anions are the dominant source of trap states in II–VI and III–V QDs and that passivation with Lewis acidic Z-type ligands is a general strategy to fix those traps. Our work also provides a method to tune the PL QY of QD samples from nearly zero up to near-unity values, without the need to grow epitaxial shells.

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“…The PbI -hybrid-amine matrix leads to CQD inks with an improved colloidal stability ( Supplementary Fig. 9) that benefit from the enhanced steric repulsion 23,24 of the longer amine surfactants (hexylamine). We also observed narrower PL peaks and higher PL quantum yields from hybrid-amine inks ( Supplementary Fig.…”

Section: Nature Nanotechnologymentioning

confidence: 99%

2D matrix engineering for homogeneous quantum dot coupling in photovoltaic solids

et al. 2018

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Colloidal quantum dots (CQDs) are promising photovoltaic (PV) materials because of their widely tunable absorption spectrum controlled by nanocrystal size. Their bandgap tunability allows not only the optimization of single-junction cells, but also the fabrication of multijunction cells that complement perovskites and silicon . Advances in surface passivation, combined with advances in device structures , have contributed to certified power conversion efficiencies (PCEs) that rose to 11% in 2016 . Further gains in performance are available if the thickness of the devices can be increased to maximize the light harvesting at a high fill factor (FF). However, at present the active layer thickness is limited to ~300 nm by the concomitant photocarrier diffusion length. To date, CQD devices thicker than this typically exhibit decreases in short-circuit current (J) and open-circuit voltage (V), as seen in previous reports. Here, we report a matrix engineering strategy for CQD solids that significantly enhances the photocarrier diffusion length. We find that a hybrid inorganic-amine coordinating complex enables us to generate a high-quality two-dimensionally (2D) confined inorganic matrix that programmes internanoparticle spacing at the atomic scale. This strategy enables the reduction of structural and energetic disorder in the solid and concurrent improvements in the CQD packing density and uniformity. Consequently, planar devices with a nearly doubled active layer thicknesses (~600 nm) and record values of J (32 mA cm) are fabricated. The V improved as the current was increased. We demonstrate CQD solar cells with a certified record efficiency of 12%.

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Hybrid N-Butylamine-Based Ligands for Switching the Colloidal Solubility and Regimentation of Inorganic-Capped Nanocrystals

Cited by 50 publications

References 65 publications

Halide Ligands To Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness

Halide Ligands To Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness

Finding and Fixing Traps in II–VI and III–V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation

2D matrix engineering for homogeneous quantum dot coupling in photovoltaic solids

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