Electron-Conducting PbS Nanocrystal Superlattices with Long-Range Order Enabled by Terthiophene Molecular Linkers (original) (raw)
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ACS Nano, 2014
We fabricate a field-effect transistor by covalently functionalizing PbS nanoparticles with tetrathiafulvalenetetracarboxylate. Following experimental results from cyclic voltammetry and ambientpressure X-ray photoelectron spectroscopy, we postulate a near-resonant alignment of the PbS 1S h state and the organic HOMO, which is confirmed by atomistic calculations. Considering the large width of interparticle spacing, we observe an abnormally high field-effect hole mobility, which we attribute to the postulated resonance. In contrast to nanoparticle devices coupled through common short-chained ligands, our system maintains a large degree of macroscopic order as revealed by X-ray scattering. This provides a different approach to the design of hybrid organicÀinorganic nanomaterials, circumvents the problem of phase segregation, and holds for versatile ways to design ordered, coupled nanoparticle thin films.
Influence of ligand exchange on the electrical transport properties of PbS nanocrystals
physica status solidi (a), 2015
In this work, FETs are used as a research tool to study charge carrier mobilities in PbS nanocrystals (NCs) thin-films employed as semiconducting layer in bottom-gate bottomcontact (BGBC) field-effect transistors (FETs). The assynthesised NCs are surrounded by long alkyl chain ligands which act as electrical insulators. Therefore, a ligand exchange process with shorter molecules is necessary to enhance the free charges generation and transport. We used two different ligands: 1,2 ethandithiol (EDT) and 1,2,3,4-tetrabutylammonium iodide (TBAI) and studied the charge mobility of PbS NCs comparing the electrical characteristics of FETs made by exchanged NCs. We analysed also the contemporary presence of both exchanged nanocrystals on the device. All the transistors showed p-type transport behaviour, enhanced by an annealing process at 100 8C for 10 min. After this, only the TBAI-treated NCs devices showed a n-type transport, resulting in an ambipolar behaviour. Inkjet printing deposition techniques was also successfully used to deposit PbS-(TBAI) NCs and ambipolar devices were obtained. In addition, for printed devices it was found that it is possible to modulate the charge transport properties by applying surface treatment to the substrate with a pentafluorothiophenol (PFTP). Indeed in this case, the p-type transport was suppressed while n-type behaviour was induced.
Exclusive Electron Transport in Core@Shell PbTe@PbS Colloidal Semiconductor Nanocrystal Assemblies
ACS Nano, 2020
Assemblies of colloidal semiconductor nanocrystals (NCs) in the form of thin solid films leverage the size-dependent quantum confinement properties and the wet chemical methods, vital for the development of the emerging solution-processable electronics, photonics and optoelectronics technologies. The ability to control the charge carrier transport in the colloidal NC assemblies is fundamental for altering their electronic and optical properties for the desired applications. Here we demonstrate a strategy to render the solids of narrow-bandgap NC assemblies exclusively electron-transporting by creating type-II heterojunction via shelling. Electronic transport of molecularly cross
Effect of Ligand Structure on the Optical and Electronic Properties of Nanocrystalline PbSe Films
The Journal of Physical Chemistry C, 2012
Films of nanocrystalline PbSe were fabricated with a set of structurally varied short-chain dicarboxylic acids. Oxidation rates were studied via NIR spectroscopy to determine the effect of the structure of the diacid ligands on film stability under ambient conditions. Ligands favoring a non-bridging bonding mode were found to provide the best protection against oxidation, while among ligands expected to bridge between adjacent nanocrystals in the films, those with shorter chain lengths conferred better oxidative stability. Electronic coupling was observed as a red shift in the optical data of the ground excitonic peak of the PbSe films and found to be strongly influenced by the structure of the ligand. Transport measurements were made in air using thin-film transistors that were treated with a thin Al 2 O 3 coating via remote plasma ALD. Films prepared using fumaric, maleic, and oxalic acids yielded mobility numbers of 2.5 × 10 −5 , 3.7 × 10 −5 , and 1.6 × 10 −3 cm 2 / V·s, respectively. Results suggest that the internanocrystal distance is the major contributor to electron mobility through the nanocrystalline films, while the electronic coupling is heavily influenced by multiple factors related to the structure of the surface ligands in addition to the internanocrystal distance.
Chemical communications (Cambridge, England), 2017
We simultaneously surface-functionalize PbS nanocrystals with Cu 4,4',4'',4'''-tetraaminophthalocyanine and assemble this hybrid material into macroscopic monolayers. Electron microscopy and X-ray scattering reveal a granular mesocrystalline structure with strong coherence between the atomic lattice and the superlattice of nanocrystals within each domain. Terahertz spectroscopy and field-effect transistor measurements indicate efficient coupling of holes throughout the hybrid thin film, in conjunction with a pronounced photoresponse. We demonstrate the potential of this material for optoelectronic applications by fabricating a light-effect transistor.
Zeitschrift für Physikalische Chemie, 2018
We use derivatives of the photochromic molecule 1,2-bis(5′-carboxy-2′-methylthien-3′-yl)-cyclopentene in combination with semiconducting PbS nanocrystals to probe the feasibility of solid-state optical switching in hybrid nanostructured thin films. X-ray photoelectron spectroscopy is applied to differentiate between the different constituents in the blends, while field-effect transistor measurements in the dark reveal the effect of prior illumination with visible or ultra-violet light on the transport properties. By analyzing the response of the electric conductivity, the carrier concentration and mobility separately, we are able to distinguish between the effect of additional photo-excited charge carriers and photo-induced changes of the electronic structure of the semiconducting film. Our results suggest that coupling between the nanocrystals and the photochromic molecule is weak but also provide evidence that photochromism of the molecules may be partially preserved.
Electron transport in iodide-capped core@shell PbTe@PbS colloidal nanocrystal solids
Applied Physics Letters, 2020
Research in the field of colloidal semiconductor nanocrystals (NCs) has progressed tremendously, mostly because of their exceptional optoelectronic properties. Core@shell NCs, in which one or more inorganic layers overcoat individual NCs, recently received significant attention due to their remarkable optical characteristics. Reduced Auger recombination, suppressed blinking, and enhanced carrier multiplication are among the merits of core@shell NCs. Despite their importance in device development, the influence of the shell and the surface modification of the core@shell NC assemblies on the charge carrier transport remains a pertinent research objective. Type-II PbTe@PbS core@shell NCs, in which exclusive electron transport was demonstrated, still exhibit instability of their electron transport. Here, we demonstrate the enhancement of electron transport and stability in PbTe@PbS core@shell NC assemblies using iodide as a surface passivating ligand. The combination of the PbS shelling and the use of the iodide ligand contributes to the addition of one mobile electron for each core@shell NC. Furthermore, both electron mobility and on/off current modulation ratio values of the core@shell NC field-effect transistor are steady with the usage of iodide. Excellent stability in these exclusively electron-transporting core@shell NCs paves the way for their utilization in electronic devices.
Size-Dependent Electron Transfer from Colloidal PbS Nanocrystals to Fullerene
The Journal of Physical Chemistry Letters, 2010
We investigate a promising organic/inorganic hybrid composite for solution-processable optoelectronics made by lead sulphide nanoparticles and fullerene derivatives, which combine the sensitivity of PbS to the infrared spectrum with the good electron transport properties of fullerenes. Charge separation is the crucial process that determines whether the heterojunction can be the building block for devices converting photogenerated excitons into free charges flowing in a circuit. Subpicosecond spectroscopy techniques on bulk heterojunctions between PbS nanocrystals of various sizes and [6,6]-phenyl-61-butyric acid methyl ester (PCBM) were employed to reveal the ultrafast dynamics of photoexcited carriers, particularly transfer of photoexcited electrons from nanocrystals to PCBM. Electron transfer is found to critically depend on nanoparticle size, occurring for nanocrystals with diameter 4.4 nm and smaller, not for larger ones. Our findings are relevant to the engineering of hybrid solar cells and light detectors based on PbS nanocrystal/fullerene bulk heterojunctions.
In situ study of the formation mechanism of two-dimensional superlattices from PbSe nanocrystals
Nature Materials, 2016
Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order 1,2. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals 3,4 , as one misaligned attachment would disrupt the 2D order beyond repair. Here, we demonstrate the formation mechanism of 2D PbSe superstructures with square geometry by using in situ grazing-incidence X-ray scattering (small angle and wide angle), ex situ electron microscopy, and Monte Carlo simulations. We observed nanocrystal adsorption at the liquid/gas interface, followed by the formation of a hexagonal nanocrystal monolayer. The hexagonal geometry transforms gradually through a pseudo-hexagonal phase into a phase with square order, driven by attractive interactions between the {100} planes perpendicular to the liquid substrate, which maximize facetto-facet overlap. The nanocrystals then attach atomically via a necking process, resulting in 2D square superlattices. Oriented atomic attachment of colloidal nanocrystals (NCs), that is, the formation of a single crystal by atomic connection of smaller crystals, is an important process in geology 5-8 , and recently gained much attention as a preparation tool in semiconductor nanoscience 9,10. We reported a method to prepare 2D atomically coherent PbSe superlattices, starting from a suspension of PbSe NCs 1,2. The NCs have the shape of a truncated cube, consistent with the rock salt crystal structure of PbSe (see Supplementary Fig. 1). A suspension of these NCs is cast onto a surface of an immiscible liquid, ethylene glycol, and the solvent is evaporated at room temperature. During the evaporation, extended sheets are formed with a thickness of one NC monolayer 1. The 2D structure shows a nanoscale geometry with square periodicity with, to some extent, also atomic coherency. In this so-called square geometry, all NCs are directed with a 100 axis perpendicular to the 2D plane, and are laterally connected via the in-plane {100} facets. This means that two out of six {100} facets,
Carrier Transport in PbS and PbSe QD Films Measured by Photoluminescence Quenching
The Journal of Physical Chemistry C, 2014
The temperature-dependent quantum yield of photoluminescence (PL) has been measured in films of various sizes of PbS and PbSe quantum dots (QDs) capped with alkanedithiol ligands with lengths varying from 4 to 20 Å. We demonstrate that PL within QD films can provide information about transport in a regime that is relevant to solar photoconversion. The ligand-length dependent PL quenching reveals behavior similar to that of ligand-length dependent carrier mobility determined from field-effect transistor (FET) measurements in the dark. The data are described by a model in which band tail luminescence is quenched upon thermal activation by charge separation and hopping followed by nonradiative recombination. We extract the tunneling parameter β and find values of 1.1 ± 0.2 Å −1 except for a value of 0.7 for the smallest QD sample. Changes in the transport mechanism may be due to unique surface faceting or QD-ligand coupling that occurs in small QDs. Furthermore, we compare all-organic capped PbS QD films with those infilled by Al 2 O 3 , discovering a surprisingly small value of β less than 0.3 for the latter, which may be related to a graded potential barrier because of amorphous Al 2 O 3 at the QD surface or interfacial chemistry inherent in the atomic layer deposition process.