Robust, Functional Nanocrystal Solids by Infilling with Atomic Layer Deposition

Liu, Yao; Gibbs, Markelle; Perkins, Craig L.; Tolentino, Jason; Zarghami, Mohammad H.; Bustamante, Jorge Luis; Law, Matt

doi:10.1021/nl2028848

Cited by 149 publications

(212 citation statements)

References 28 publications

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“…Distinguishing the nature of trap states in these studies may be done spectroscopically 49 and with transmission electron microscopy 50 . 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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“…One approach to this end is to devise better methods of passivation, and indeed, some of the best performing devices to date rely on novel passivation strategies. 1,17,113 Unexplored territory exists, however, in the possibility of compensating native space charge with comparable amounts of immobile charge of opposite polarity. Even a modest result, reducing the charge density by a factor of 10 has, the potential to create cells with W scr greater than the 1 μm needed to absorb most of the incident solar spectrum.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

Engel

Alivisatos

2013

Chem. Mater.

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A semiconductor nanocrystal film is a unique class of nanocomposite, whose collective properties are determined by those of its constituents. Colloidal synthetic methods offer precise size control and finely tuned optical properties via quantum confinement, while recent improvements in charge transport through films have led to a variety of optoelectronic applications. However, understanding the role of defects and impurities in doping, crucial for optimizing device performance, has remained more elusive. In this perspective, we review recent progress in understanding and controlling the doping of semiconductor nanocrystal thin films, with a special focus on its relevance to photovoltaic applications. We highlight an array of postsynthetic techniques based on stoichiometric control, metal impurity incorporation, and electrochemical charging. We conclude with a review of the state of the art for nanocrystal photovoltaics, and propose the use of controlled doping and charge balance as a pathway to higher device efficiencies.

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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.…”

mentioning

confidence: 99%

“…Moreover, these high-mobility FETs are stable indefinitely in air ( Figure 6) because, as we recently demonstrated, the ALD infill and overcoat form an extremely effective gas diffusion barrier that stops oxidation and inhibits internal diffusion within the films. 28 These sulfide-treated, ALD-infilled PbSe QD FETs are the first high-mobility, air stable PbX QD solids and should be useful in the development of high-performance QD optoelectronic devices.…”

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confidence: 99%

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.

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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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Robust, Functional Nanocrystal Solids by Infilling with Atomic Layer Deposition

Cited by 149 publications

References 28 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

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

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

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Robust, Functional Nanocrystal Solids by Infilling with Atomic Layer Deposition

Cited by 149 publications

References 28 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

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

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

Contact Info

Product

Resources

About

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