538 research outputs found
Evaluation of Metal Phosphide Nanocrystals as Anode Materials for Na-ion Batteries
Sodium-ion batteries (SIBs) are potential low-cost alternatives to lithium-ion batteries (LIBs) because of the much greater natural abundance of sodium salts. However, developing high-performance electrode materials for SIBs is a challenging task, especially due to the ?50% larger
ionic radius of the Na+ ion compared to Li+, leading to vastly different electrochemical behavior. Metal phosphides such as FeP, CoP, NiP2, and CuP2 remain unexplored as electrode materials for SIBs, despite their high theoretical charge storage
capacities of 900â1300 mAh gâ1. Here we report on the synthesis of metal phosphide nanocrystals (NCs) and discuss their electrochemical properties as anode materials for SIBs, as well as for LIBs. We also compare the electrochemical characteristics of phosphides with
their corresponding sulfides, using the environmentally benign iron compounds, FeP and FeS2, as a case study. We show that despite the appealing initial charge storage capacities of up to 1200 mAh gâ1, enabled by effective nanosizing of the active electrode materials, further work toward optimization of the electrode/electrolyte pair is needed to improve the electrochemical performance upon cycling
Coherent spin dynamics of electrons and holes in CsPbBr perovskite crystals
The lead halide perovskites demonstrate huge potential for optoelectronic
applications, high energy radiation detectors, light emitting devices and solar
energy harvesting. Those materials exhibit strong spin-orbit coupling enabling
efficient optical orientation of carrier spins in perovskite-based devices with
performance controlled by a magnetic field. Perovskites are promising for
spintronics due to substantial bulk and structure inversion asymmetry, however,
their spin properties are not studied in detail. Here we show that elaborated
time-resolved spectroscopy involving strong magnetic fields can be successfully
used for perovskites. We perform a comprehensive study of high-quality
CsPbBr crystals by measuring the exciton and charge carrier -factors,
spin relaxation times and hyperfine interaction of carrier and nuclear spins by
means of coherent spin dynamics. Owing to their "inverted" band structure,
perovskites represent appealing model systems for semiconductor spintronics
exploiting the valence band hole spins, while in conventional semiconductors
the conduction band electrons are considered for spin functionality.Comment: 8 pages, 3 figures + supplementary informatio
Scalable fabrication of efficient p-n junction lead sulfide quantum dot solar cells
Nowadays, the best lead sulfide (PbS) colloidal quantum dot (CQD) solar cells are primarily demonstrated in the n-p structure, while the p-n structure is significantly less developed. This technological gap between the n-p and p-n structures is much more distinct than in cases of other solution-processable photovoltaic technologies like perovskites and polymers. Here, we propose a scalable fabrication strategy for efficient PbS QD solar cells with p-n structure. An industrially suited blade-coating technique has been used to deposit both n-type and p-type QD layers. The obtained solar cells demonstrated power conversion efficiency of 9%, thus, commensurate to the record device efficiency with this architecture fabricated with a non-scalable technique. The availability of both p-n and n-p structures fabricated from scalable methods may promote the future integration of the PbS QDs into tandem devices together with other solution-processable materials to exploit the most prominent benefits of the PbS QDs, such as infrared absorption.</p
Impact of Crystal Structure and Particles Shape on the Photoluminescence Intensity of CdSe/CdS Core/Shell Nanocrystals
To study the influence of the chemical and crystalline composition of core/shell NCs on their photoluminescence (PL) the mean structural profile of a large ensemble of NCs has to be retrieved in atomic resolution. This can be achieved by retrieving the chemical profile of core/shell NCs using anomalous small angle x-ray scattering (ASAXS) in combination with the analysis of powder diffraction data recorded by wide angle x-ray scattering (WAXS). In the current synchrotron based study, we investigate CdSe/CdS core/shell NCs with different core dimensions by recording simultaneously ASAXS and WAXS spectra. The CdS shells are grown epitaxial on nominal spherical CdSe cores with core diameters from around 3.5â5.5 nm. Three different CdSe shell thicknesses are realized by depositing around 4, 6, and 8 monolayers (MLs) of CdSe. We reveal that the epitaxial core/shell structure depicts a chemical sharp interface, even after a post growth annealing step. With increasing NC diameter, however, the CdSe/CdS NCs deviate significantly from a spherical shape. Instead an elliptical particle shape with pronounced surface facets for the larger core/shell NCs is found. In combination with the powder diffraction data we could relate this anisotropic shape to a mixture of crystal phases within the CdSe core. The smallest CdSe cores exhibit a pure hexagonal wurtzite crystal structure, whereas the larger ones also possess a cubic zincblende phase fraction. This mixed crystal phase fractions lead to a non-spherical shell growth with different thicknesses along specific crystallographic directions: The long axes are terminated by basal crystal faces parallel either to the a- or c-axis, the short axes by âtiltedâ pyramidal planes. By combining these structural data with the measured PL quantum yield values, we can clearly connect the optical output of the NCs to their shape and to their shell thickness. Above 6 ML CdS shell-thickness no further increase of the PL can be observed, but for large aspect ratio values the PL is significantly decreased. The gained understanding of the internal crystal structure on CdSe/CdS NCs is general applicable for a precise tuning of the optical properties of crystalline core/shell NCs
High-resolution remote thermography using luminescent low-dimensional tin-halide perovskites
While metal-halide perovskites have recently revolutionized research in
optoelectronics through a unique combination of performance and synthetic
simplicity, their low-dimensional counterparts can further expand the field
with hitherto unknown and practically useful optical functionalities. In this
context, we present the strong temperature dependence of the photoluminescence
(PL) lifetime of low-dimensional, perovskite-like tin-halides, and apply this
property to thermal imaging with a high precision of 0.05 {\deg}C. The PL
lifetimes are governed by the heat-assisted de-trapping of self-trapped
excitons, and their values can be varied over several orders of magnitude by
adjusting the temperature (up to 20 ns {\deg}C-1). Typically, this sensitive
range spans up to one hundred centigrade, and it is both compound-specific and
shown to be compositionally and structurally tunable from -100 to 110 {\deg} C
going from [C(NH2)3]2SnBr4 to Cs4SnBr6 and (C4N2H14I)4SnI6. Finally, through
the innovative implementation of cost-effective hardware for fluorescence
lifetime imaging (FLI), based on time-of-flight (ToF) technology, these novel
thermoluminophores have been used to record thermographic videos with high
spatial and thermal resolution.Comment: 25 pages, 4 figure
An overview and prospective on Al and Al-ion battery technologies
Aluminum batteries are considered compelling electrochemical energy storage systems because of the natural abundance of aluminum, the high charge storage capacity of aluminum of 2980 mA h gâ1/8046 mA h cmâ3, and the sufficiently low redox potential of Al3+/Al. Several electrochemical storage technologies based on aluminum have been proposed so far. This review classifies the types of reported Al-batteries into two main groups: aqueous (Al-ion, and Al-air) and non-aqueous (aluminum graphite dual-ion, Al-organic dual-ion, Al-ion, and Al-sulfur). Specific focus is given to Al electrolyte chemistry based on chloroaluminate melts, deep eutectic solvents, polymers, and âchlorine-freeâ formulations
Double Gate PbS Quantum Dot Field-Effect Transistors for Tuneable Electrical Characteristics
In this work colloidal quantum dots double gate transistors are introduced. A high-k (k = 43) relaxor ferroelectric polymer is used as a dielectric material for the top gate in a device where the other gate is fabricated from SiO2. The device in double gate configuration is characterized by reduced hysteresis in the transfer curves measured by separately sweeping the voltage of the SiO2 and of the polymer gate. Gating with the relaxor polymer leads to mobility values of ÎŒe = 1.1 cm2 Vâ1sâ1 and ÎŒh = 6 Ă 10â3 cm2 Vâ1sâ1 that exceed those extracted from the SiO2 gating: ÎŒe = 0.5 cm2 Vâ1sâ1 and ÎŒh = 2 Ă 10â3 cm2 Vâ1sâ1. Measurements under double gating conditions prove that the device works in a single channel mode that is delocalized over the whole film thickness. Double gating allows for shifting the threshold voltage into a desired position and also allows increasing the on-current of the devices
Opto-electronics of PbS quantum dot and narrow bandgap polymer blends
Here we report on the interaction between the narrow bandgap polymer [2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and lead sulphide (PbS) colloidal quantum dots (CQDs) upon photoexcitation. We show that the presence of both materials in a blend leads to a significant reduction of photoluminescence (PL) lifetime of the polymer. This observation is attributed, supported by transient absorption (TA) data, to an efficient electron transfer towards the QDs for excitons generated on the polymer. Furthermore, the ligand capping the QD surface exhibits a great impact on the dynamics of the PL, with the long-chain oleic acid (OA) largely suppressing any kind of interaction. By means of external quantum efficiency (EQE) measurements we find evidence that both components give rise to a contribution to the photocurrent, making this an interesting blend for future applications in hybrid organic-inorganic solar cells.</p
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