High Carrier Concentration Research Articles

Dark Current Mechanisms and Suppression Strategies for Infrared Photodetectors Based on Two‐Dimensional Materials

AbstractNarrow‐bandgap 2D materials and semimetals, for example, graphene, black phosphorus (BP), tellurium (Te), and some novel transition metal dichalcogenides (TMDs), have been demonstrated to be promising building blocks for constructing next‐generation state‐of‐the‐art infrared (IR) photodetectors. However, these devices suffer from a significant dark current, primarily attributed to the intrinsic thermal excitation‐induced high carrier concentration. Suppressing the dark current is an essential issue in pursuing higher specific detectivity of IR photodetectors. Here, the authors demonstrate recent advances in suppressing dark current for 2D IR photodetectors. First, a brief insight into the dark current composition and mechanisms of 2D IR photodetectors is illustrated. Then, the varied band alignment for blocking dark current by the interfacial barrier is discussed. Next, localized electric field modulation by applying a gate voltage and ferroelectric materials is discussed. This method can effectively tune the concentration and distribution of carriers in the device conductive channel. Following that, interfacial engineering is summarized, by which interfacial defects can be passivated and interlayer defect‐induced dark current can be suppressed. Finally, the challenges and an outlook are delivered for developing state‐of‐the‐art IR photodetectors.

Carrier Screening Controls Transport in Conjugated Polymers at High Doping Concentrations.

Transport properties of doped conjugated polymers (CPs) have been widely analyzed with the Gaussian disorder model (GDM) in conjunction with hopping transport between localized states. These models reveal that even in highly doped CPs, a majority of carriers are still localized because dielectric permittivity of CPs is well below that of inorganic materials, making Coulomb interactions between carriers and dopant counterions much more pronounced. However, previous studies within the GDM did not consider the role of screening the dielectric interactions by carriers. Here we implement carrier screening in the Debye-Hückel formalism in our calculations of dopant-induced energetic disorder, which modifies the Gaussian density of states (DOS). Then we solve the Pauli master equation using Miller-Abrahams hopping rates with states from the resulting screened DOS to obtain conductivity and Seebeck coefficient across a broad range of carrier concentrations and compare them to measurements. Our results show that screening has significant impact on the shape of the DOS and consequently on carrier transport, particularly at high doping. We prove that the slope of Seebeck coefficient versus electric conductivity, which was previously thought to be universal, is impacted by screening and decreases for systems with small dopant-carrier separation, explaining our measurements. We also show that thermoelectric power factor is underestimated by a factor of ∼10 at higher doping concentrations if screening is neglected. We conclude that carrier screening plays a crucial role in curtailing dopant-induced energetic disorder, particularly at high carrier concentrations.

Influence of substrate temperature on the properties of ZnTe:Cu films prepared by a magnetron co-sputtering method

Copper-doped Zinc Tellurium (ZnTe:Cu) films were deposited on borosilicate glass using magnetron co-sputtering technique. The influence of the substrate temperature on the structural, morphological, optical and electrical properties of ZnTe:Cu films was investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV–Vis spectrophotometer and Hall effect measurement system. The results indicate that substrate temperature significantly affects the properties of the ZnTe:Cu films. When the substrate temperature increases from room temperature to 600 °C, the (111)-preferred orientation of ZnTe:Cu films is gradually replaced by the (220)-preferred orientation. At high substrate temperatures (≥500 °C), the CuxTe phase appears in the ZnTe:Cu films, resulting in higher carrier concentration (>1019 cm−3) and lower resistivity (<10−2 Ω cm) of the prepared films.

High-Performance and Ecofriendly Organic Thermoelectrics Enabled by N-Type Polythiophene Derivatives with Doping-Induced Molecular Order.

The ability of n-type polymer thermoelectric materials to tolerate high doping loading limits further development of n-type polymer conductivity. Herein, two alcohol-soluble n-type polythiophene derivatives that are n-PT3 and n-PT4 are reported. Due to the ability of two polymers to tolerate doping loading more significantly than 100mol%, both achieve electrical conductivity >100Scm-1 . Moreover, the conductivity of both polythiophenes remains almost constant at high doping concentrations with excellent doping tunability, which may be related to their ability to overcome charging-induced backbone torsion and morphology change caused by saturated doping. The characterizations reveal that n-PT4 has a high doping level and carrier concentration (>3.10×1020 cm-3 ), and the carrier concentration continues to increase as the doping concentration increases. In addition, doping leads to improved crystal structure of n-PT4, and the crystallinity does not decrease significantly with increasing doping concentration; even the carrier mobility increases with it. The synergistic effect of these two leads to both n-PT3 and n-PT4 achieving a breakthrough of 100 in conductivity and power factor. The DMlmC-doped n-PT4 achieves a power factor of over 150µWm-1 K-2 . These values are among the highest for n-type organic thermoelectric materials.

Multifunctional GeMnTe2 Synergistically Optimizes Thermoelectric Properties of SnTe-In2Te3 Alloys.

SnTe-In2Te3 alloys ensure excellent electrical properties in the whole temperature region due to the resonant level. Nevertheless, temperature-sensitive resonance states and single phonon scattering restrict further improvement of thermoelectric performance. Consequently, it is anticipated that additional electrically independent scattering sources should be introduced to impede phonon transport. Here, the SnTe-In2Te3-GeMnTe2 alloy is prepared by further solidifying cubic GeMnTe2, which demonstrates multiple modulation effects. The highly redissolved Mn2+ promotes the valence band convergence, enhances the Seebeck coefficient at higher temperature, and balances the possible weakened resonance level effect at higher carrier concentrations, and a high average power factor (1.94 mW m-1 K-2) is realized over the entire temperature range. Additionally, compensatory vacancies, substitutions, and Ge/Mn precipitates are easily constructed with GeMnTe2 alloying, leading to a further reduction in lattice thermal conductivity, which reaches κl ∼ 0.6 W m-1 K-1 at 850 K. Ultimately, a high peak zT of ∼1.25 (850 K) and a zTave of 0.72 (300-850 K) are realized in (SnTe)2.91(In2Te3)0.03(Ge0.5Mn0.5Te)1.2, and the maximum thermoelectric conversion efficiency of ∼2.8% (ΔT ∼ 450 K) is achieved. The present results indicate multiple effects of GeMnTe2 in enhancing the thermoelectric performance of SnTe-In2Te3 alloys.

Al-delta-doped ZnO films made by atomic layer deposition and flash-lamp annealing for low-emissivity coating

In this work, we have investigated and optimized the Al-delta-doped ZnO (δ -AZO) superlattices for mid-infrared applications. Thin films of δ -AZO are fabricated by atomic layer deposition (ALD) followed by millisecond-range (ms-range) flash-lamp annealing (FLA). During the FLA process, the superlattice structure is preserved and Al is electrically activated. The highest carrier concentration and lowest resistivity estimated from Hall-effect measurements are 2.7 × 1021 cm−3 and 8.8 × 10-4 Ωcm, respectively, for the δ -AZO superlattice with an Al:Zn ratio of 1:20. Moreover, glass substrates coated with the developed δ -AZO superlattice show a reflectance above 60 % in the near- and mid-infrared spectral range, while the transmittance in the visible range maintains above 80 %. The presented δ -AZO superlattice is a good alternative material to replace indium tin oxide films for cost-efficient low-emissivity glazing.

Efficient Carrier Transport in 2D Bi2O2Se/CsBi3I10 Perovskite Heterojunction Enables Highly-Sensitive Broadband Photodetection.

2D Bi2O2Se has recently garnered significant attention in the electronics and optoelectronics fields due to its remarkable photosensitivity, broad spectral absorption, and excellent long-term environmental stability. However, the development of integrated Bi2O2Se photodetector with high performance and low-power consumption is limited by material synthesis method and the inherent high carrier concentration of Bi2O2Se. Here, a type-I heterojunction is presented, comprising 2D Bi2O2Se and lead-free bismuth perovskite CsBi3I10, for fast response and broadband detection. Through effective charge transfer and strong coupling effect at the interfaces of Bi2O2Se and CsBi3I10, the response time is accelerated to 4.1 µs, and the detection range is expanded from ultraviolet to near-infrared spectral regions (365-1500nm). The as-fabricated photodetector exhibits a responsivity of 48.63 AW-1 and a detectivity of 1.22×1012 Jones at 808nm. Moreover, efficient modulation of the dominant photocurrent generation mechanism from photoconductive to photogating effect leads to sensitive response exceeding 103 AW-1 for heterojunction-based photo field effect transistor (photo-FETs). Utilizing the large-scale growth of both Bi2O2Se and CsBi3I10, the as-fabricated integrated photodetector array demonstrates outstanding homogeneity and stability of photo-response performance. The proposed 2D Bi2O2Se/CsBi3I10 perovskite heterojunction holds promising prospects for the future-generation photodetector arrays and integrated optoelectronic systems.

A ZnO-002/amorphous Bi2WO6 heterojunction with enhanced electron-hole separation for high-performance Cr(VI) photoreduction

The difference in bandgap structure results in better charge separation performance of crystalline/amorphous heterojunctions compared to a single component. Considering that the catalytic activity of metal oxides is often accompanied by differences in facets, it has become an interesting topic to further improve the charge separation performance of such heterojunctions by adjusting the facets at the material contact interface. This article synthesized three novels ZnO/amorphous Bi2WO6 heterojunctions with specific facets (ZnO-101/aBi2WO6, ZnO-100/aBi2WO6 and ZnO-002/aBi2WO6) by adding ZnO with different facets to bismuth tungstate precursors through hydrothermal methods. Photoelectric testing shows that compared to a single component, all three heterojunctions display efficient carrier separation characteristics. Among them, the ZnO/aBi2WO6 heterojunction with the 002 facet exhibits more excellent performance, such as photocatalytic reduction of 150 mg·L−1 Cr(VI) without hole scavenger. The system spectral and energy spectrum characterization shows that the matched band structure induces a strong built-in electric field, which accelerates the separation of bulk carriers. And meanwhile, many oxygen vacancies, high specific surface area, low interface resistance and high concentration of carriers also provide help for the treatment of pollutants. In addition, 94.49 % of the photocatalytic activity was retained after 5 cycles, which proved the excellent photo cycling stability of the heterojunction.

High sensitivity of semimetal photodetection via Bose–Einstein condensation

AbstractThe discovery of semiconductor has witnessed remarkable strides toward high performance of photodetectors attributed to its excellent carrier properties. However, semimetal, owning to the high carrier concentration and low carrier mobility compared to those of semiconductor, is generally considered unsuitable for photodetection. Herein, we demonstrate an outstanding photodetection in a layered semimetal titanium diselenide (TiSe2) in Bose–Einstein condensation (BEC) state. High sensitivity of semimetal photodetector is realized in the range of visible, infrared and terahertz bands. The noise equivalent power (NEP) has threefold improvement at the visible and infrared wavebands, and significant decrease by one order of magnitude in the terahertz frequencies via BEC phenomenon, attributed to the electrical parameter variation after condensation. The best NEP value in the terahertz frequency is comparable to that of commercial Si photodetector. Our results show another recipe to fabricate high performance of photodetection via semimetal except for semiconductor and pave the way to exploit macroscopic quantum phenomena for optoelectronics.image

Constructing the relationship between microstructure and piezocatalysis in (K, Na)NbO3 lead-free piezocatalyst

Piezocatalysis converts mechanical vibration into chemical energy and holds great potential for wastewater treatment and biomedical applications. Although the influence of microstructure on piezocatalysis is well recognized, its relationship has been rarely investigated in potassium sodium niobate ((K, Na)NbO3, KNN), an emerging lead-free and eco-friendly piezocatalyst. In this study, we modified the synthesis conditions of (K0.48Na0.52)NbO3-0.3 %Fe2O3 (KNN-Fe) material to produce KNN-Fe piezocatalysts with different microstructure characteristics. We then examined the relationship between microstructure and piezocatalysis by assessing the degradation of Rhodamine B (RhB) and methyl orange (MO) dyes. The KNN-Fe piezocatalyst with an 8 h-sand-ground shows the reaction rate constant (k) values of 79 × 10−3 min−1 and 27.12 × 10−3 min−1 for the degradation of RhB and MO, respectively. These values are 16 % and 303 % higher than those of the sand-ground-0 h sample. The enhanced piezocatalysis of the sand-ground-8 h sample stems from the increased specific surface area and oxygen vacancies, enhanced separation of electron-hole pairs, and higher carrier concentration. This study not only elucidates the relationship between microstructure and piezocatalysis in KNN materials but also suggests a potential approach for enhancing piezocatalytic activity.

Enhancing Thermoelectric Performance in P-Type Sb2Te3-Based Compounds Through Nb─Ag Co-Doping with Donor-Like Effect.

P-type Sb2Te3 has been recognized as a potential thermoelectric material for applications in low-medium temperature ranges. However, its inherent high carrier concentration and lattice thermal conductivity led to a relatively low ZT value, particularly around room temperature. This study addresses these limitations by leveraging high-energy ball milling and rapid hot-pressing techniques to substantially enhance the Seebeck coefficient and power factor of Sb2Te3, yielding a remarkable ZT value of 0.55 at 323K due to the donor-like effect. Furthermore, the incorporation of Nb─Ag co-doping increases hole concentration, effectively suppressing intrinsic excitations ≈548K while maintaining the favorable power factor. Simultaneously, the lattice thermal conductivity can be significantly reduced upon doping. As a result, the ZT values of Sb2Te3-based materials attain an impressive range of 0.5-0.6 at 323K, representing an almost 100% improvement compared to previous research endeavors. Finally, the ZT value of Sb1.97Nb0.03Ag0.005Te3 escalates to 0.92 at 548K with a record average ZT value (ZTavg) of 0.75 within the temperature range of 323-573K. These achievements hold promising implications for advancing the viability of V-VI commercialized materials for low-medium temperature application.

AlGaN High Electron Mobility Transistor for High Temperature Logic

We report on AlGaN HEMT-based logic development, using combined enhancement- and depletion-mode transistors to fabricate inverters with operation from room temperature up to 500°C. Our development approach included: (a) characterizing temperature dependent carrier transport for different AlGaN HEMT heterostructures, (b) developing a suitable gate metal scheme for use in high temperatures, and (c) over-temperature testing of discrete devices and inverters. Hall mobility data revealed the GaN-channel HEMT experienced a 6.9× reduction in mobility, whereas the AlGaN channel HEMTs experienced about a 3.1x reduction. Furthermore, a greater aluminum contrast between the barrier and channel enabled higher carrier densities in the two-dimensional electron gas for all temperatures. The combination of reduced variation in mobility with temperature and high sheet carrier concentration showed that an Al-rich AlGaN-channel HEMT with a high barrier-to-channel aluminum contrast is the best option for an extreme temperature HEMT design. Three gate metal stacks were selected for low resistivity, high melting point, low thermal expansion coefficient, and high expected barrier height. The impact of thermal cycling was examined through electrical characterization of samples measured before and after rapid thermal anneal. The 200 nm tungsten gate metallization was the top performer with minimal reduction in drain current, a slightly positive threshold voltage shift, and about an order of magnitude advantage over the other gates in on-to-off current ratio. After incorporating the tungsten gate metal stack in device fabrication, characterization of transistors and inverters from room temperature up to 500°C was performed. The enhancement-mode (e-mode) devices’ resistance started increasing at about 200°C, resulting in drain current degradation. This phenomenon was not observed in depletion-mode (d-mode) devices but highlights a challenge for inverters in an e-mode driver and d-mode load configuration.

Tungsten-Doped Indium Tin Oxide Thin-Film Transistors for Dual-mode Proximity Sensing Application.

Technologies for human-machine interactions are booming now. In order to achieve multifunctional sensing abilities of electronic skins, further developments of various sensors are in urgent demand. Herein, a dual-mode proximity sensor based on an oxide thin-film transistor (TFT) is reported. Although InSnO (ITO) is featured with high mobility, the inherent high carrier concentration limits its use as a channel material for thin-film transistors. Herein, the tungsten element was introduced as a carrier suppressor to develop ITO-based semiconducting materials and devices. TFTs with amorphous tungsten-doped ITO (ITWO) channel layers were fabricated. As for a flat panel display application, the TFT device from 250 °C-annealed ITWO layer with an atomic ratio of In/Sn/W = 86:9:5 presented the optimal device performance with carrier mobility of 11.53 cm2 V-1 s-1, swing subthreshold of 0.66 V dec-1, threshold voltage of -2.18 V, and Ion/Ioff ratio of 3.33 × 107 and much small hysteresis of transfer characteristic. ITWO TFT devices were further developed as dual-mode proximity sensors that could work with both extended-gate and compact configurations, where the drain current was directly related to the surface potential of a charged object and the distance between the sensing end and the object, enabling the proximity sensing of charged stimuli. For extended-gate-configured proximity sensing, a charged object modulated the formation of a conductive channel at the semiconductor/SiO2 interface, while this conductive channel occurred at the semiconductor/air interface for compact-configured sensing. Formation of the conductive channel of the compact transistor was modulated by the electric field component in the direction perpendicular to the interface, and the drain current was sensitive to the orientation of the approaching object, which implied the capacity of angle sensing to the approach of a charged object. This work further emphasizes that the basic device performance should be optimized according to its specific application scenarios rather than only considering the requirements of the panel display.

The Mechanism Behind the High zT of SnSe&lt;sub&gt;2&lt;/sub&gt; Added SnSe at High Temperatures

SnSe is a promising thermoelectric material due to its low toxicity, low thermal conductivity, and multiple valence band structures, which are ideal for high electronic transport properties. The multiple valence band structure has attracted many attempts to engineer the carrier concentration of the SnSe via doping, to place its fermi level at a position where the maximum number of valence bands can participate in the electronic transport. Up until now, ~5 × 10&lt;sup&gt;19&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt; was the highest carrier concentration achieved in SnSe via doping. Recently, introducing SnSe&lt;sub&gt;2&lt;/sub&gt; into SnSe was found to effectively increase the carrier concentration as high as ~6.5 × 10&lt;sup&gt;19&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt; (at 300 K) due to the generated Sn vacancies. This high carrier concentration at 300 K, combined with the reduction in lattice thermal conductivity due to SnSe&lt;sub&gt;2&lt;/sub&gt; micro-domains formed within the SnSe lattice, improved the thermoelectric performance (&lt;i&gt;zT&lt;/i&gt;) of SnSe – &lt;i&gt;x&lt;/i&gt;SnSe&lt;sub&gt;2&lt;/sub&gt; as high as ~2.2 at 773 K. Here, we analyzed the changes in the electronic band parameters of SnSe as a function of temperature with varying SnSe&lt;sub&gt;2&lt;/sub&gt; content using the Single Parabolic Band (SPB) model. According to the SPB model, the calculated density-of-states effective mass and the fermi level are changed with temperature in such a way that the Hall carrier concentration (&lt;i&gt;nH&lt;/i&gt;) of the SnSe – xSnSe2 samples at 773 K coincides with the optimum &lt;i&gt;nH&lt;/i&gt; where the theoretically maximum &lt;i&gt;zT&lt;/i&gt; is predicted. To optimize the &lt;i&gt;nH&lt;/i&gt; at high temperatures for the highest &lt;i&gt;zT&lt;/i&gt;, it is essential to tune the 300 K &lt;i&gt;nH&lt;/i&gt; and the rate of &lt;i&gt;nH&lt;/i&gt; change with increasing temperature via doping.

Morphology matters: Investigating the influence of granules and nanofibers on the physicochemical properties of TiO2 for optoelectronic applications

This study investigated the influence of morphology on the physiochemical properties of TiO2, specifically comparing granule-like structures and nanofibers. Both morphologies were fabricated using different methods and characterized comprehensively. After annealing, X-ray diffraction confirmed their crystalline nature with peaks corresponding to the anatase phase of titania. Scanning electron microscopy revealed long nanofibers with diameters ranging from 62 nm to 95 nm, while the granules appeared as spherical or nearly spherical particles with sizes between 43 nm and 59 nm. Energy-dispersive X-ray analysis confirmed the presence of Ti and O in both structures. The Fourier-transform infrared and raman spectra exhibited characteristic bands related to the Ti–O–Ti stretching, vibrational, binding and anatase phase of titania, respectively. Raman peaks' intensity and position were influenced by crystal size, quality, and strain. The nanofibers showed higher raman mode peak intensities due to their larger surface area to volume ratio and high aspect ratio. In UV–Vis–NIR spectra, the nanofibers displayed higher absorption and a narrower bandgap than the granules. Hall Effect measurements indicated that the nanofibers had a higher carrier concentration and conductivity than the granules. Additionally, the nanofibers exhibited hydrophobic behavior with a water contact angle of 95°, while the granules were relatively hydrophilic with a contact angle of 58o. The findings could potentially facilitate the creation of customized TiO2 materials that are better suited for specific optoelectronic devices. This advancement would result in improved overall efficiency and performance across a range of technological uses.

Zirconium doped zinc oxide thin films grown by spray pyrolysis technique for TCO applications

Zirconium (Zr) doped Zinc Oxide (ZnO) thin films were grown on pre-cleaned glass substrates by spray pyrolysis technique. The dopant was added in different concentrations to study its influence on the structural, optical, morphological, and electrical properties of ZnO thin films. X- Ray Diffractogram (XRD) data was used to study the structural properties of all the thin films. It was found that the crystallite size varied between 25 and 45 nm for dopant at different concentrations. Additionally, it was discovered that ZnO possessed a hexagonal wurtzite structure with (002) as its preferred orientation regardless of the doping doses. The optical properties for all the thin films were obtained by analysing the absorption spectra. The transmittance of all the thin films ranged between 65 % and 86 % in the visible range with 4 at % Zr doped ZnO having highest transmittance. Scanning Electron Microscopy (SEM) results showed the agglomeration of particles at higher concentrations of the dopant. Electrical studies showed that the resistivity of the doped samples decreased as compared to the pristine sample. Sample with 6 % of doping had the highest carrier concentration and hence, showed the least resistivity of 67 Ω cm.

Annealing-free fabrication of high-quality indium tin oxide films for free-carrier-based hybrid metal–semiconductor nanophotonics

Recent discoveries have revealed that indium tin oxide (ITO), due to the presence of an epsilon-near-zero (ENZ) point and suitable carrier concentration and mobility, can be used to modulate the refractive index, confine fields in the nanoscale, enhance nonlinear effects, achieve ultrafast light switching or to construct so-called time-varying media. While this potential positions ITO as a key material for future nanophotonic devices, producing ITO films with precisely engineered properties remains a significant challenge. Especially when the device’s complex geometry or incorporated materials require the fabrication process to be conducted at substrate temperatures below 100 °C and without any post-annealing treatment. Here we present a comprehensive study on the low-temperature deposition of 70 nm thick ITO films using an e-beam PVD system. The nanolayers evaporated under different conditions were characterized by SEM and AFM microscopy, Hall effect measurement system as well as spectroscopic ellipsometry. We discuss the factors influencing the optical, electrical, and morphological properties of ITO films. We show that smooth nanolayers of similar quality to annealed samples can be obtained at 80 °C by controlling the oxygen plasma parameters, and the ENZ wavelength can be tuned throughout the NIR spectral range. Finally, we show that using the proposed methodology, we fabricated ITO films with resistivity as low as 5.2 × 10–4 Ω cm, smooth surface with RMS < 1 nm, high carrier concentration reaching 1.2 × 1021 cm−3 and high transmittance (85%) in the Vis/NIR spectrum.

Realizing Remarkable Improvement of Electrical Performance in N‐Type BiSbSe3 via In Situ Compositing

AbstractBiSbSe3 is a Te‐free thermoelectric material with intrinsically low thermal conductivity. Its thermoelectric performance is limited by poor electrical conductivity. To optimize electrical conductivity, Bi2SbSe3 with high carrier concentration and mobility is introduced to BiSbSe3 matrix through in situ reaction and conventional mechanical mixing. In both methods, carrier concentrations are improved by carrier injection and redistribution. Carrier mobility is manipulated based on microstructure. In the conventional method, isolated flake‐shaped Bi2SbSe3 grains with weak‐bonding phase boundaries restrict carrier mobility. For the in situ method, irregular Bi2SbSe3 connects into conductive networks inducing a percolation effect, and in situ formed small‐angle phase boundaries barely impede carriers. Thus, the carrier mobilities of in situ composites are significantly improved and higher than that of conventional composites. Simultaneously optimized carrier concentration and mobility remarkably enhance electrical conductivity over the whole working temperature. Maximum electrical conductivity of 378 S cm−1 is achieved in BiSbSe3‐38 vol% Bi2SbSe3 in situ composites at 300 K, obtaining more than 300% improvement compared with 124 S cm−1 in BiSbSe3 matrix. Lattice thermal conductivity is reduced at a low compositing fraction. Ultimately, a record‐breaking average ZT of 0.65 (300–750 K) is attained in BiSbSe3‐13 vol% Bi2SbSe3 in situ composite. The in situ compositing method in this work effectively optimizes electrical performance, anticipated to be applied in other thermoelectric materials.

Dilute Sc/Y doping in SnTe for efficient charge transport modulation and high thermoelectric performance

As a highly potential environmental-friendly medium-temperature thermoelectric material, pure SnTe exhibits relatively poor performance due to its intrinsic high carrier concentration and large energy offset between the two valence bands. In the present work, dilute Sc/Y doping is innovatively adopted to synergistically decrease carrier concentration and achieve strong band convergence. The Hall measurement results indicate that 3 % Y doping realizes the lowest carrier concentration of 2.6 × 1019 cm−3 in SnTe. Sc and Y have similar effects in promoting band convergence, with their effects second only to toxic Hg elements at the same doping concentration. The effective decoupling of electrical and thermal transport parameters results in a high average ZT of 0.453 for Sn0.975Sc0.025Te sample, which is 103 % higher than that of pure SnTe. In addition, with Li2Te alloying to regulate carrier concentration, high-performance temperature range could be adjusted, which is more conducive to dealing with different temperature scenarios. The role of Sc/Y doping disclosed in this work provides more options for further improving the performance of SnTe-based materials.

Solvothermally silver doping boosting the thermoelectric performance of polycrystalline Bi2Te3

Bismuth telluride (Bi2Te3) is one of the most promising thermoelectric materials for commercial application at room temperature, but the thermoelectric performance of these materials still needs to be improved. In this study, we report a type of solvothermally Ag-doped Bi2Te3 microplate. By sintering these microplates into polycrystalline bulk materials, a high room-temperature figure of merit of 1 has been achieved. Based on comprehensive micro/nanostructural characterizations, we found that the solvothermally doped Ag in Bi2Te3 plays two main roles, namely as the dopants that effectively induce the point defects of AgBi and forming Ag2Te nanophases. AgBi can provide additional hole charge carriers, effectively adjusting the initially high electron carrier concentration in the system, while the Ag2Te nanophases effectively trigger energy filtering effect to maintain a high Seebeck coefficient, thereby contributing to a competitively high power factor of 25.5 μW cm−1 K−2 at 298 K. Simultaneously, a low thermal conductivity of 0.74 W m−1 K−1 is obtained due to the strong phonon scattering at various lattice imperfections, induced by the solvothermally Ag-doping, which include point defects, grain/phase boundaries, local lattice distortions, and dislocations. This work fills the gap in knowledge on the solvothermally Ag-doping mechanism in Bi2Te3 and provides guidance for the innovative design of high-performing inorganic thermoelectrics.