Abstract
Two-dimensional (2D) materials and their corresponding van der Waals heterostructures have drawn tremendous interest due to their extraordinary electrical and optoelectronic properties. ...Insulating 2D hexagonal boron nitride (
h
-BN) with an atomically smooth surface has been widely used as a passivation layer to improve carrier transport for other 2D materials, especially for Transition Metal Dichalcogenides (TMDCs). However, heat flow at the interface between TMDCs and
h
-BN, which will play an important role in thermal management of various electronic and optoelectronic devices, is not yet understood. In this paper, for the first time, the interface thermal conductance (G) at the MoS
2
/
h
-BN interface is measured by Raman spectroscopy, and the room-temperature value is (17.0 ± 0.4) MW · m
−2
K
−1
. For comparison, G between graphene and
h
-BN is also measured, with a value of (52.2 ± 2.1) MW · m
−2
K
−1
. Non-equilibrium Green’s function (NEGF) calculations, from which the phonon transmission spectrum can be obtained, show that the lower G at the MoS
2
/
h
-BN interface is due to the weaker cross-plane transmission of phonon modes compared to graphene/
h
-BN. T
h
is study demonstrates that the MoS
2
/
h
-BN interface limits cross-plane heat dissipation, and thereby could impact the design and applications of 2D devices while considering critical thermal management.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
As an emerging member in 2D materials, pentagonal palladium diselenide (PdSe2) has interesting ambipolar charge transport behavior with high air‐stability and shows great potential in nanoelectronics ...and optoelectronics. Moreover, the puckered pentagon structure in PdSe2 results in an intrinsic low lattice thermal conductivity, which makes PdSe2 a superior material prospect for thermoelectric (TE) applications. However, its TE properties have yet to be experimentally demonstrated. Here, the TE transport in 2D PdSe2 with a low‐symmetry pentagonal lattice is probed for the first time. By thickness‐engineering, it is demonstrated that the TE property of PdSe2 can be effectively manipulated due to its sensitive dependence on the interlayer coupling originating from the special lattice structure. The TE performance can be largely enhanced benefiting from the high band convergence and quantum confinement in thinner PdSe2 flakes. A power factor as high as 1.5 mW m−1 K−2 can be achieved for a PdSe2 flake with a thickness of 5 nm. This work provides the first TE study on a pentagonal lattice as opposed to hexagonal lattices that dominate the 2D layered material family. The unique lattice structure with special interlayer interaction in PdSe2 opens up new pathways for TE applications, low‐dimensional electronics, and quantum devices.
The thermoelectric (TE) transport in 2D palladium diselenide (PdSe2) with a low‐symmetry pentagonal lattice is probed. Due to its sensitive dependence on the interlayer coupling originating from the special lattice structure, the TE performance can be largely enhanced benefiting from the high band convergence and quantum confinement through thickness engineering.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Thermoelectric materials have the ability to convert heat energy to electrical power and vice versa. While the thermodynamic upper limit is defined by the Carnot efficiency, the material figure of ...merit, zT, is far from this theoretical limit, typically limited by a complex interplay of non-equilibrium charge and phonon-scattering. Materials innovation is a slow, arduous process due to the complex correlations between crystal structure, microstructure engineering, and thermoelectric properties. Many physical concepts and materials have been unearthed in this path to discovery, supported ably by innovations in technology over many decades, revealing important material and transport descriptors. In this review, we look back at some case studies of inorganic thermoelectric materials employing a bird’s-eye view of complementary advancements in scientific concepts and technological advancements and conclude that most high values of zT have emerged from developed scientific models fueled by moderately mature technologies. On the basis of this conclusion, we then propose that the recent emergence of data-driven approaches and high-throughput experiments, encompassing synthesis as well as characterization, with machine learning guided inverse design is perfectly suited to provide an accelerated pathway toward the discovery of next-generation thermoelectric materials, potentially providing a feasible alternative source of energy for a sustainable future.
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IJS, KILJ, NUK, PNG, UL, UM
The presence of high crystallographic symmetry and nanoscale defects are favorable for thermoelectrics. With proper electronic structures, a highly symmetric crystal tends to possess multiple carrier ...channels and promote electrical conductivity without sacrificing Seebeck coefficient. In addition, nanoscale defects can effectively scatter acoustic phonons to suppress thermal conductivity. Here, it is reported that the triple doping of Cu2SnSe3 leads to a high ZT value of 1.6 at 823 K for Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3, and a decent average ZT (ZTave) value of 0.7 is also achieved for Cu1.85Ag0.15(Sn0.93Mg0.06Na0.01)Se3 from 475 to 823 K. This study reveals: 1) Ag doping on Cu sites generates numerous point defects and greatly decreases lattice thermal conductivity. 2) Doping Mg or Ga converts the monoclinic Cu2SnSe3 into a cubic structure. This symmetry enhancing leads to an increase in the effective mass from 0.8 me to 2.6 me (me, free electron mass) and the power factor from 4.3 µW cm−1 K−2 for Cu2SnSe3 to 11.6 µW cm−1 K−2. 3) Na doping creates dense dislocation arrays and nanoprecipitates, which strengthens the phonon scattering. 4) Pair distribution function analysis shows localized symmetry breakdown in the cubic Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3. This work provides a standpoint to design promising thermoelectric materials by synergistically manipulating crystal symmetry and nanoscale defects.
The highest ZT value of 1.6 at 823 K is achieved in the diamondoid compound Cu2SnSe3 by a triple doping strategy. Crystal symmetry enhanced from monoclinic to cubic leads to band convergence, favorable for electrical properties. The existence of nanoscale defects effectively decreases lattice thermal conductivity. The joint effect produces the highest ZT value in thermoelectric materials with diamondoid structures.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Black phosphorus (BP) has emerged as a promising candidate for next‐generation electronics and optoelectronics among the 2D family materials due to its extraordinary electrical/optical/optoelectronic ...properties. Interestingly, BP shows strong anisotropic transport behavior because of its puckered honeycomb structure. Previous studies have demonstrated the thermal transport anisotropy of BP and theoretically attribute this to the anisotropy in both the phonon dispersion relation and the phonon relaxation time. However, the exact origin of such strong anisotropy lacks clarity and has yet to be proven experimentally. Here, the thermal transport anisotropy of BP nanoribbons is probed by an electron beam technique. Direct evidence is provided that the origin of this anisotropy is dominated by the anisotropic phonon group velocity, verified by Young's modulus measurements along different directions. It turns out that the ratio of the thermal conductivity between zigzag (ZZ) and armchair (AC) ribbons is almost same as that of the corresponding Young modulus values. The results from first‐principles calculation are consistent with this experimental observation, where the anisotropic phonon group velocity between ZZ and AC is shown. These results provide fundamental insight into the anisotropic thermal transport in low‐symmetry crystals.
The anisotropic thermal transport of black phosphorus nanoribbons is studied. Direct evidence is provided that the origin of this anisotropy is dominated by the anisotropic phonon group velocity, verified by Young's modulus measurements along different directions. These results provide fundamental insight into the anisotropic thermal transport in low‐symmetry crystals.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Successful materials innovations can transform society. However, materials research often involves long timelines and low success probabilities, dissuading investors who have expectations of shorter ...times from bench to business. A combination of emergent technologies could accelerate the pace of novel materials development by ten times or more, aligning the timelines of stakeholders (investors and researchers), markets, and the environment, while increasing return on investment. First, tool automation enables rapid experimental testing of candidate materials. Second, high-performance computing concentrates experimental bandwidth on promising compounds by predicting and inferring bulk, interface, and defect-related properties. Third, machine learning connects the former two, where experimental outputs automatically refine theory and help define next experiments. We describe state-of-the-art attempts to realize this vision and identify resource gaps. We posit that over the coming decade, this combination of tools will transform the way we perform materials research, with considerable first-mover advantages at stake.
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The convergence of high-performance computing, automation, and machine learning promises to accelerate the rate of materials discovery by ≥10 times, better aligning investor and stakeholder timelines. Infrastructure and human-capital investments are discussed, including equipment capabilities, data management, education, and incentives. As our field transitions from thinking “data poor” to thinking “data rich,” we envision a scientific laboratory where the process of materials discovery continues without disruptions, aided by computational power augmenting the human mind, and freeing the latter to perform research closer to the speed of imagination, addressing societal challenges in market-relevant timeframes.
A combination of emergent technologies promises to accelerate novel materials development by ten times or more: tool automation, high-performance computing, and machine learning. We describe state-of-the-art attempts to realize this vision and identify resource gaps, including required infrastructure and human-capital investments.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Intensive research in electrochemical CO
2
reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these ...catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO
2
reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO
2
reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.
Hybrid (organic-inorganic) materials have emerged as a promising class of thermoelectric materials, achieving power factors (S
σ) exceeding those of either constituent. The mechanism of this ...enhancement is still under debate, and pinpointing the underlying physics has proven difficult. In this work, we combine transport measurements with theoretical simulations and first principles calculations on a prototypical PEDOT:PSS-Te(Cu
) nanowire hybrid material system to understand the effect of templating and charge redistribution on the thermoelectric performance. Further, we apply the recently developed Kang-Snyder charge transport model to show that scattering of holes in the hybrid system, defined by the energy-dependent scattering parameter, remains the same as in the host polymer matrix; performance is instead dictated by polymer morphology manifested in an energy-independent transport coefficient. We build upon this language to explain thermoelectric behavior in a variety of PEDOT and P3HT based hybrids acting as a guide for future work in multiphase materials.
Establishing the relationship between pressure and heat–electricity interconversion in van der Waals bonded small‐molecule organic semiconductors is critical not only in designing flexible ...thermoelectric materials, but also in developing organic electronics. Here, based on first‐principles calculations and using naphthalene as a case study, an unprecedented elevation of p‐type thermoelectric power factor induced by pressure is demonstrated; and the power factor increases by 267% from 159.5 µW m−1 K−2 under ambient conditions to 585.8 µW m−1 K−2 at 2.1 GPa. The underlying mechanism is attributed to the dramatic inhibition of lattice‐vibration‐caused electronic scattering. Furthermore, it is revealed that both restraining low‐frequency intermolecular vibrational modes and increasing intermolecular electronic coupling are two essential factors that effectively suppress the electron–phonon scattering. From the standpoint of molecular design, these two conditions can be achieved by extending the π‐conjugated backbones, introducing long alkyl sidechains to the π‐cores, and substituting heteroatoms in the π‐cores.
An unprecedented pressure‐induced enhancement of the thermoelectric power factor in small‐molecule organic semiconductors is demonstrated; the fundamental reason for this is the dramatic inhibition of electron–phonon scattering. Both suppression of low‐frequency lattice vibrations and increase of electronic couplings are essential factors that suppress electron–phonon scattering, and these two conditions can be achieved by extending the π‐cores, introducing alkyl sidechains to the π‐cores, and substituting heteroatoms in the π‐cores.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The past few decades have seen an uptick in the scope and range of device applications of organic semiconductors, such as organic field-effect transistors, organic photovoltaics and light-emitting ...diodes. Several researchers have studied electrical transport in these materials and proposed physical models to describe charge transport with different material parameters, with most disordered semiconductors exhibiting hopping transport. However, there exists a lack of a consensus among the different models to describe hopping transport accurately and uniformly. In this work, we first evaluate the efficacy of using a purely data-driven approach, i.e., symbolic regression, in unravelling the relationship between the measured field-effect mobility and the controllable inputs of temperature and gate voltage. While the regressor is able to capture the scaled mobility well with mean absolute error (MAE) ~ O(10
), better than the traditionally used hopping transport model, it is unable to derive physically interpretable input-output relationships. We then examine a physics-inspired renormalization approach to describe the scaled mobility with respect to a scale-invariant reference temperature. We observe that the renormalization approach offers more generality and interpretability with a MAE of the ~ O(10
), still better than the traditionally used hopping model, but less accurate as compared to the symbolic regression approach. Our work shows that physics-based approaches are powerful compared to purely data-driven modelling, providing an intuitive understanding of data with extrapolative ability.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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