Repairing Nanoparticle Surface Defects

Marino, Emanuele; Kodger, Thomas E.; Crisp, Ryan W.; Timmerman, Dolf; MacArthur, Katherine E.; Heggen, Marc; Schall, Peter

doi:10.1002/anie.201705685

Cited by 24 publications

(33 citation statements)

References 26 publications

(22 reference statements)

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“…Furthermore, studies utilizing charged X-type ligands to transfer QDs from nonpolar to polar media do not result in increases of PL QY. 23 − 28 One study by Page et al 8 claimed near-unity PL QYs in CdTe QDs as a result of X-type passivation of Cd sites by Cl – anions from added CdCl 2 , but we note that their results can be explained via Z-type passivation of Te sites by CdCl 2 . 29 , 30 L-type amine ligands pose a more significant counter-argument against the hypothesis that only a two-coordinated anion results in trap states, as they are commonly observed to increase the PL QY of CdSe QDs.…”

Section: Introductionmentioning

confidence: 52%

“… 20 However, our results show that if Cd traps exist, they must contribute less to nonradiative recombination than Te traps and are removed by the addition of MX n ligands. (ii) Some surface reconstruction follows binding of Cl or other ligands, 28 resulting in a reduction of two-coordinated Te sites. We observed no sign of morphology changes in our treatment experiments, but this does not rule out reconstruction of the QD surface.…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 52%

Section: Resultsmentioning

confidence: 99%

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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“…The increase of Φ( t )∑μ with increasing fluence is not typically observed in films of Pb- or Cd-chalcogenide QDs, although it has been observed by Savenije et al 40 for TiO 2 nanoparticles and has been attributed to filling of deep traps. Related, Marino et al 41 have shown that for CdSe nanoplatelets the PL, surface defects (deep traps), and TRMC mobility are correlated. Such deep traps quickly capture charge carriers within the 3 ns time resolution of the TRMC experiment and hence lower the maximum Φ( t )∑μ value that is measured.…”

Section: Results and Discussionmentioning

confidence: 95%

Highly Photoconductive InP Quantum Dots Films and Solar Cells

Crisp

Kirkwood

Grimaldi

et al. 2018

ACS Appl. Energy Mater.

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InP and InZnP colloidal quantum dots (QDs) are promising materials for application in light-emitting devices, transistors, photovoltaics, and photocatalytic cells. In addition to possessing an appropriate bandgap, high absorption coefficient, and high bulk carrier mobilities, the intrinsic toxicity of InP and InZnP is much lower than for competing QDs that contain Cd or Pb–providing a potentially safer commercial product. However, compared to other colloidal QDs, InP QDs remain sparsely used in devices and their electronic transport properties are largely unexplored. Here, we use time-resolved microwave conductivity measurements to study charge transport in films of InP and InZnP colloidal quantum dots capped with a variety of short ligands. We find that transport in InP QDs is dominated by trapping effects, which are mitigated in InZnP QDs. We improve charge carrier mobilities with a range of ligand-exchange treatments and for the best treatments reach mobilities and lifetimes on par with those of PbS QD films used in efficient solar cells. To demonstrate the device-grade quality of these films, we construct solar cells based on InP & InZnP QDs with power conversion efficiencies of 0.65 and 1.2%, respectively. This represents a large step forward in developing Cd- and Pb-free next-generation optoelectronic devices.

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“…In addition to the transition metal oxides and transition metal salts, various layered 2D materials also show great attractiveness. For example, the metal chalcogenides, such as SnS 2 , WS 2 , CoS 2 , WS 2 , [121] and 2D-MOFs, like Mn-, Ni-, Co-2D MOF nanosheets [122] have been applied in LIBs and/or KIBs. Especially, MXenes, a large family of 2D transition metal carbides and carbonitrides, discovered by Gogotsis group, [123] have gained widespread interest as emerging potential host anode materials for DIBs, due to their unique structure, high theoretical capacity (447.8, 351.8, 191.8 mAh g À1 for LIB, NIB, and KIB on Ti 3 C 2 , respectively), [124] and adjustable interlayer space capable of accommodating cations with large ionic radius, such as Na + and K + .…”

Section: D Layered Materialsmentioning

confidence: 99%

Strategies towards Low‐Cost Dual‐Ion Batteries with High Performance

et al. 2019

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Rocking‐chair based lithium‐ion batteries (LIBs) have extensively applied to consumer electronics and electric vehicles (EVs) for solving the present worldwide issues of fossil fuel exhaustion and environmental pollution. However, due to the growing unprecedented demand of LIBs for commercialization in EVs and grid‐scale energy storage stations, and a shortage of lithium and cobalt, the increasing cost gives impetus to exploit low‐cost rechargeable battery systems. Dual‐ion batteries (DIBs), in which both cations and anions are involved in the electrochemical redox reaction, are one of the most promising candidates to meet the low‐cost requirements of commercial applications, because of their high working voltage, excellent safety, and environmental friendliness compared to conventional rocking‐chair based LIBs. However, DIB technologies are only at the stage of fundamental research and considerable effort is required to improve the energy density and cycle life further. We review the development history and current situation, and discuss the reaction kinetics involved in DIBs, including various anionic intercalation mechanism of cathodes, and the reactions at the anodes including intercalation and alloying to explore promising strategies towards low‐cost DIBs with high performance.

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Repairing Nanoparticle Surface Defects

Cited by 24 publications

References 26 publications

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

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

Highly Photoconductive InP Quantum Dots Films and Solar Cells

Strategies towards Low‐Cost Dual‐Ion Batteries with High Performance

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