Lead sulfide, a compound consisting of elements with high natural abundance, can be converted into an excellent thermoelectric material. We report extensive doping studies, which show that the power ...factor maximum for pure n-type PbS can be raised substantially to ∼12 μW cm–1 K–2 at >723 K using 1.0 mol % PbCl2 as the electron donor dopant. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding selected metal sulfide phases. The thermal conductivity at 723 K can be reduced by ∼50%, 52%, 30%, and 42% through introduction of up to 5.0 mol % Bi2S3, Sb2S3, SrS, and CaS, respectively. These phases form as nanoscale precipitates in the PbS matrix, as confirmed by transmission electron microscopy (TEM), and the experimental results show that they cause huge phonon scattering. As a consequence of this nanostructuring, ZT values as high as 0.8 and 0.78 at 723 K can be obtained for nominal bulk PbS material. When processed with spark plasma sintering, PbS samples with 1.0 mol % Bi2S3 dispersion phase and doped with 1.0 mol % PbCl2 show even lower levels of lattice thermal conductivity and further enhanced ZT values of 1.1 at 923 K. The promising thermoelectric properties promote PbS as a robust alternative to PbTe and other thermoelectric materials.
Most of recent research on layered chalcogenides is understandably focused on single atomic layers. However, it is unclear if single-layer units are the most ideal structures for enhanced gas–solid ...interactions. To probe this issue further, we have prepared large-area MoS2 sheets ranging from single to multiple layers on 300 nm SiO2/Si substrates using the micromechanical exfoliation method. The thickness and layering of the sheets were identified by optical microscope, invoking recently reported specific optical color contrast, and further confirmed by AFM and Raman spectroscopy. The MoS2 transistors with different thicknesses were assessed for gas-sensing performances with exposure to NO2, NH3, and humidity in different conditions such as gate bias and light irradiation. The results show that, compared to the single-layer counterpart, transistors of few MoS2 layers exhibit excellent sensitivity, recovery, and ability to be manipulated by gate bias and green light. Further, our ab initio DFT calculations on single-layer and bilayer MoS2 show that the charge transfer is the reason for the decrease in resistance in the presence of applied field.
Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to ...reduce the thermal conductivity. Recently, (PbTe)1–x (PbSe) x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1–x (PbS) x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1–2x (PbSe) x (PbS) x system. The (PbTe)1–2x (PbSe) x (PbS) x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe–PbSe–PbS 2% Na doped are superior to those of 2% Na-doped PbTe–PbSe and PbTe–PbS, respectively, achieving a ZT ≈2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 μW/cmK2. The very low total thermal conductivity values of 1.1 W/m·K of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures.
Herein, we report a significantly improved thermoelectric figure of merit ZT of ∼1.1 at ∼923 K in p-type SnTe through In2Te3 alloying and iodine doping. We propose that the introduction of indium at ...Sn sites in SnTe creates resonant levels inside the valence bands, thereby considerably increasing the Seebeck coefficients and power factors in the low-to-middle temperature range. Unlike SnTe–InTe, the SnTe–In2Te3 system displays much lower lattice thermal conductivity. Utilizing a model for point defect scattering, we analyze the origin of the low thermal conductivity in SnTe–In2Te3 and attribute it mainly to the strong vacancy originated phonon scattering between Sn atoms and the vacancies introduced by In2Te3 alloying and partly to the interfacial scattering by In-rich nanoprecipitates present in SnTe matrix. By alloying only In2Te3 with SnTe, a ZT value of ∼0.9 at 923 K was achieved. ZT can be further increased to ∼1.1 at 923 K through adjusting the charge carriers by iodine doping at Te sites.
Sb‐doped and GeTe‐alloyed n‐type thermoelectric materials that show an excellent figure of merit ZT in the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable ...changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single‐phase solid solution (SS) or two‐phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density‐of‐states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κlat). Specifically, the Seebeck coefficient of Pb0.988Sb0.012Te–13%GeTe–Nano approaches −280 µV K−1 at 673 K with a low κlat of 0.56 W m−1 K−1 at 573 K. Consequently, a peak ZT value of 1.38 is achieved at 623 K. Moreover, a high average ZTavg value of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb0.988Sb0.012Te–13%GeTe–Nano.
Both supersaturated solid solutions and nanostructured n‐type Pb1−xGexTe systems with excellent thermoelectric performance can be prepared via a nonequilibrium process. The nanostructured sample enhances the figure of merit ZT via reducing the lattice thermal conductivity. A ZTavg of ≈1.04 is obtained, which is among the highest ZTavg values for n‐type PbTe materials reported so far.
Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ...ion vacancies to maximize charge transfer. Here nonconjugated multi‐zwitterionic small‐molecule electrolytes (NSEs) are introduced, which act not only as charge‐extracting layers for barrier‐free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom‐up passivation effect. Implementing these synergistic properties affords NSE‐based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum VOC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light‐soaking stability. Thus, this work demonstrates that the bottom‐up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.
Nonconjugated multi‐zwitterionic small‐molecule electrolyte (NSE) molecules in perovskite solar cells (PSCs) act not only as both charge‐extracting layers for barrier‐free cathode charge collection but also as charged defect fillers in perovskite bulk and interfaces by spontaneous bottom‐up passivation. Thus, the NSE‐based PSCs deliver PCEs as high as 21.18% with an ultrahigh VOC of 1.19 V, suppressed hysteresis, and enhanced stability.
Low-cost and efficient electrocatalysts for overall water splitting are in high demand for a wide range of applications across renewable and clean energy. Here, we report a simple one-step synthesis ...of a three-dimensional (3D) carbon-coated Ni8P3 nanosheet array as bifunctional catalyst for both hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). The nanosheet array possesses low overpotentials, high current densities, and small Tafel slopes in both HER and OER and shows high electrocatalytic activities and long-term stability. The carbon layer with high electric conductivity serves not only as a protective layer to prevent Ni8P3 dissolution but also as an active layer to decrease the electrocatalysis overpotential. The nanosheet array has HER outstanding activity in both acid and alkaline media. Its superior performance in OER can be due to the synergistic interaction at the Ni8P3/NiO x heterojunction. Furthermore, cell voltage as low as 1.65 V can achieve 10 mA cm–2 current density for full water splitting in an alkaline water electrolyzer, indicating potential application of C@ Ni8P3 as bifunctional catalyst for clean and renewable energy utilization.
DNA programmable assembly has been combined with top-down lithography to construct superlattices of discrete, reconfigurable nanoparticle architectures on a gold surface over large areas. ...Specifically, the assembly of individual colloidal plasmonic nanoparticles with different shapes and sizes is controlled by oligonucleotides containing "locked" nucleic acids and confined environments provided by polymer pores to yield oriented architectures that feature tunable arrangements and independently controllable distances at both nanometer- and micrometer-length scales. These structures, which would be difficult to construct by other common assembly methods, provide a platform to systematically study and control light-matter interactions in nanoparticle-based optical materials. The generality and potential of this approach are explored by identifying a broadband absorber with a solvent polarity response that allows dynamic tuning of visible light absorption.
Crystalline defects are commonly generated in lithium-metal-oxide electrodes during cycling of lithium-ion batteries. Their role in electrochemical reactions is not yet fully understood because, ...until recently, there has not been an effective operando technique to image dynamic processes at the atomic level. In this study, two types of defects were monitored dynamically during delithiation and concomitant oxidation of oxygen ions by using in situ high-resolution transmission electron microscopy supported by density functional theory calculations. One stacking fault with a fault vector b/6110 and low mobility contributes minimally to oxygen release from the structure. In contrast, dissociated dislocations with Burgers vector of c/2001 have high gliding and transverse mobility; they lead to the formation, transport and release subsequently of oxygen related species at the surface of the electrode particles. This work advances the scientific understanding of how oxygen participates and the structural response during the activation process at high potentials.
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