Fabrication of All-Inorganic Nanocrystal Solids through Matrix Encapsulation of Nanocrystal Arrays

Kinder, Erich; Moroz, Pavel; Diederich, Geoffrey; Johnson, Alexa; Kirsanova, Maria A.; Nemchinov, Alexander; O’Connor, Timothy; Roth, Dan; Zamkov, Mikhail

doi:10.1021/ja208670r

Cited by 52 publications

(70 citation statements)

References 100 publications

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“…The as-prepared films may be post treated with inorganic passivations-using methods such as atomic layer deposition 51 or successive ion layer adsorption and reaction 36 -to infiltrate the film and fully passivate any remaining bare surface sites. Another route to such a matrix could include fusing shell materials from core-shell nanoparticles via sintering 52 .…”

Section: Discussionmentioning

confidence: 99%

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

et al. 2014

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Colloidal quantum dots are attractive materials for efficient, low-cost and facile implementation of solution-processed optoelectronic devices. Despite impressive mobilities (1-30 cm 2 V À 1 s À 1 ) reported for new classes of quantum dot solids, it is-surprisingly-the much lower-mobility (10 À 3 -10 À 2 cm 2 V À 1 s À 1 ) solids that have produced the best photovoltaic performance. Here we show that it is not mobility, but instead the average spacing among recombination centres that governs the diffusion length of charges in today's quantum dot solids. In this regime, colloidal quantum dot films do not benefit from further improvements in charge carrier mobility. We develop a device model that accurately predicts the thickness dependence and diffusion length dependence of devices. Direct diffusion length measurements suggest the solid-state ligand exchange procedure as a potential origin of the detrimental recombination centres. We then present a novel avenue for in-solution passivation with tightly bound chlorothiols that retain passivation from solution to film, achieving an 8.5% power conversion efficiency.

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Section: Discussionmentioning

confidence: 99%

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

et al. 2014

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“…27,28 The aim of the ALD coating is to serve as a gas diffusion barrier to stop oxidation, a nanoscale cement to inhibit solid-state diffusion within the films, and an electronic matrix that passivates surface states and reduces the size of the inter-QD tunnel barrier governing charge transport in QD films. Similar aims motivate the use of MCCs 1 and other strategies 29 to engineer the interdot matrix. ALD employs alternating selfsaturating surface reactions of gas-phase precursors to deposit conformal thin films of precisely controlled thickness.…”

mentioning

confidence: 86%

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

Liu¹,

Tolentino²,

Gibbs³

et al. 2013

Nano Lett.

223

322

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PbSe quantum dot (QD) field effect transistors (FETs) with air-stable electron mobilities above 7 cm 2 V −1 s −1 are made by infilling sulfide-capped QD films with amorphous alumina using lowtemperature atomic layer deposition (ALD). This high mobility is achieved by combining strong electronic coupling (from the ultrasmall sulfide ligands) with passivation of surface states by the ALD coating. A series of control experiments rule out alternative explanations. Partial infilling tunes the electrical characteristics of the FETs. KEYWORDS: Quantum dots, nanocrystals, lead selenide, field-effect transistors, solar cells T he recent introduction of metal chalcogenide complexes (MCCs) as ligands for colloidal quantum dots (QDs) 1 has triggered a flurry of research into inorganic ligands for fabricating high-performance all-inorganic QD solids for optoelectronic applications. 2−4 In addition to several demonstrations of MCC efficacy by Talapin and co-workers, 5−8 a variety of metal-free inorganic ions including chalcogenides, 9,10 halides, 11 thiocyanate, 12−14 and trialkyl oxonium 15 have been shown in initial studies to provide generally better performance in CdX and PbX (X = S, Se, Te) QD field-effect transistors (FETs) 6,7,12−14 and solar cells 11 than the small molecules, such as hydrazine 16 and 1,2-ethanedithiol (EDT), 17,18 traditionally used to replace the long-chain insulating organic ligands inherited from QD synthesis. Ionic inorganic ligands offer several key advantages over neutral molecular ligands. First, many inorganic ligands are ultrasmall and enable strong electronic coupling between QDs in films, which favors highmobility transport. Second, inorganic ions can quantitatively replace native long-chain ligands on the QD surface to produce charge-stabilized colloidal QD suspensions in polar media, in principle allowing the direct formation of conductive QD films from solution without the need for postassembly chemical or thermal treatments that can inhibit charge transport by increasing spatial and energetic disorder in the films. In practice, however, thermal treatments (150−300°C) are typically needed to achieve good transport in all-inorganic QD solids. Also, solution-phase exchange has so far failed to yield stable all-inorganic PbX QD colloids except with select hydrazine-free MCCs or mixed chalcogenide ions, 5,13 so postassembly ("solid state") ligand exchange has been employed instead to make PbX QD devices. 10−13,15 A third advantage of inorganic ligands is that they decompose, evaporate, or assimilate into the QDs at relatively low temperatures to create functional inorganic matrices (e.g., with MCCs) or direct QD−QD contact and partial QD necking/fusion (e.g., with S 2− and SCN − ). Despite the large site energy disorder induced by such annealing, 7,14,19 the electronic properties of films made with this approach may be adequate for many applications, including high-efficiency solar energy conversion. Recent reports of record mobilities for electrons in CdSe, 7,14 holes in PbX, 12,1...

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“…43,44 By using this strategy, ligand-free metal and semiconductor domains can be placed within small distances of each other to promote the enhanced energy transfer rate. Notably, both types of nanoparticles remain electrically "insulated" due to the wide gap of the interstitial matrix (either CdS or ZnS).…”

Section: Resultsmentioning

confidence: 99%

“…The thermal removal of ligands was confirmed by FTIR. 43 The presence of CdSe NCs in the film was evident through the characteristic band gap emission of fabricated solids at λ = 620 nm (Fig. 4b, red curve).…”

Section: ) (E) a Sem Image Of A (Au Cdse) Np Filmmentioning

confidence: 95%

Exciton Generation in Semiconductor Nanocrystals via the Near-Field Plasmon Energy Transfer

et al. 2015

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The plasmon resonance of small-diameter metal nanoparticles has a unique decay character, as it produces almost no far field scattering. Instead, most of the absorbed light is emitted in the near field (NF), phenomenon also known as strong field localization. Such non-radiative emission is short lived and decays primarily via the production of heat, which prevents efficient harvesting of the NF energy.Here, we demonstrate a general strategy for coupling the NF radiation of surface plasmons to long-lived optical excitations in semiconductor nanocrystals (NCs). This concept was manifested through the observation of an enhanced exciton generation in CdSe NCs coupled to 5-nm Au nanoparticles. To distinguish the plasmon antenna effect from photoinduced charge transfer processes, both Au and CdSe nanoparticles were encapsulated into insulating CdS or ZnS matrices. A unique signature of the plasmon to exciton energy transfer was observed in photoexcitation measurements that unambiguously correlate the increase in the CdSe exciton population with the excitation of plasmon modes in Au domains. The demonstrated scheme for harvesting the NF radiation of metal nanoparticles presents an excellent opportunity for extracting the evanescent emission of surface plasmons that can find practical applications in photovoltaic or photocatalytic technologies.

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Fabrication of All-Inorganic Nanocrystal Solids through Matrix Encapsulation of Nanocrystal Arrays

Cited by 52 publications

References 100 publications

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

Exciton Generation in Semiconductor Nanocrystals via the Near-Field Plasmon Energy Transfer

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Fabrication of All-Inorganic Nanocrystal Solids through Matrix Encapsulation of Nanocrystal Arrays

Cited by 52 publications

References 100 publications

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm2 V–1 s–1

Exciton Generation in Semiconductor Nanocrystals via the Near-Field Plasmon Energy Transfer

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PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1