Highly‐Anisotropic Dion–Jacobson Hybrid Perovskite by Tailoring Diamine into CsPbBr3 for Polarization‐Sensitive Photodetection

2D materials with inherent attributes of structural anisotropy have been well applied in the field of polarization‐sensitive photodetection. However, to explore new 2D members with strong polarized‐light responses still remains a challenge. Herein, by alloying diamine molecule into the 3D prototype of CsPbBr₃, a new Dion–Jacobson (DJ) type 2D perovskite of (HDA)CsPb₂Br₇ ( 1 , where HDA²⁺ is 1,6‐hexamethylenediammonium), containing both inorganic Cs metal and organic cations is designed. The natural anisotropy characteristics of 1 are solidly elucidated by analyzing crystal structure, electric conductivity, and optical properties. Strikingly, distinct polarization‐sensitive responses are observed in 1 , owing to its strong anisotropy of optical absorption (the ratio of α_c/α_b ≈ 2.2). Consequently, crystal‐based detectors of 1 exhibit fascinating photo‐activities to polarized‐light, including high detectivity (1.5 × 10⁹ Jones), large dichroism ratio (I_ph^c/I_ph^b ≈ 1.6) and fast responding rate (200 µs). All these polarization‐sensitive performances along with intriguing phase stability make 1 a potential candidate for polarized‐light detection. This work paves a pathway toward new functionalities of DJ‐type 2D hybrid perovskites for their future optoelectronic device applications.     

A Simple Method for Synthesis of High‐Quality Millimeter‐Scale 1T′ Transition‐Metal Telluride and Near‐Field Nanooptical Properties

The controlled synthesis of MoTe₂ and WTe₂ is crucial for their fundamental research and potential electronic applications. Here, a simplified ambient‐pressure chemical vapor deposition (CVD) strategy is developed to synthesize high‐quality and large‐scale monolayer and few‐layer 1T′‐phase MoTe₂ (length ≈ 1 mm) and WTe₂ (length ≈ 350 µm) crystals by using ordinary salts (KCl or NaCl) as the growth promoter combining with low‐cost (NH₄)₆Mo₇O₂₄·4H₂O and hydrate (NH₄)₁₀W₁₂O₄₁·xH₂O as the Mo and W sources, respectively. Atomic force microscopy, X‐ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy confirm the high‐quality nature and the atomic structure of the as‐grown 1T′ MoTe₂ and WTe₂ flakes. Variable‐temperature transport measurements exhibit their semimetal properties. Furthermore, near‐field nanooptical imaging studies are performed on the 1T′ MoTe₂ and WTe₂ flakes for the first time. The sub‐wavelength effects of 1T′‐phase MoTe₂ (λ_p ≈ 140 nm) and WTe₂ (λ_p ≈ 100 nm) are obtained. This approach paves the way for the growth of special transition‐metal dichalcogenides materials and boosts the future polaritonic research of 2D telluride compounds.     

Construction of FeS2‐Sensitized ZnO@ZnS Nanorod Arrays with Enhanced Optical and Photoresponse Performances

FeS₂‐sensitized ZnO@ZnS nanorod arrays are fabricated by a two‐step solution immersion and a subsequent sulfurization. The material properties including structure, morphology, and photoluminescence are investigated by a variety of characterization methods. As compared with ZnO@ZnS core/shell structure, FeS₂‐sensitized ZnO@ZnS nanorod arrays show improved optical absorption property with the extension of the absorption edge into the range of visible light. The photoresponse performance of FeS₂‐sensitized Zno@ZnS is also enhanced as the photocurrent density at 1.0 V is dozens of times larger than that of ZnO@ZnS nanorods. The cause for the difference in such material properties of these two materials is discussed. In this work, a new method for sensitizing wide bandgap ZnO@ZnS nanorod arrays with improved light response performance is presented.     

Broadband MoS2 Field‐Effect Phototransistors: Ultrasensitive Visible‐Light Photoresponse and Negative Infrared Photoresponse

Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS₂). The devices are capable of detecting photons with energy below the bandgap of MoS₂. Under the illumination of near‐infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible‐light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 10⁴–10⁵ A W^?1 owing to the photogating effect and charge trapping mechanism. Besides, the phototransistors can detect a weak visible‐light signal with effective optical power as low as 17 picowatts (pW). A thermally induced photoresponse mechanism, the bolometric effect, is proposed as the cause of the negative photocurrent in the NIR regime. The thermal energy of the NIR radiation is transferred to the MoS₂ crystal lattice, inducing lattice heating and resistance increase. This model is experimentally confirmed by low‐temperature electrical measurements. The bolometric coefficient calculated from the measured transport current change with temperature is ?33 nA K^?1. These findings offer a new approach to develop sub‐bandgap photodetectors and other novel optoelectronic devices based on 2D layered materials.     

Phase‐Controlled Synthesis of Monolayer Ternary Telluride with a Random Local Displacement of Tellurium Atoms

Alloying 2D transition metal dichalcogenides has opened up new opportunities for bandgap engineering and phase control. Developing a simple and scalable synthetic route is therefore essential to explore the full potential of these alloys with tunable optical and electrical properties. Here, the direct synthesis of monolayer WTe_2xS_2(1?x) alloys via one‐step chemical vapor deposition (CVD) is demonstrated. The WTe_2xS_2(1?x) alloys exhibit two distinct phases (1H semiconducting and 1T ′ metallic) under different chemical compositions, which can be controlled by the ratio of chalcogen precursors as well as the H₂ flow rate. Atomic‐resolution scanning transmission electron microscopy–annular dark field (STEM‐ADF) imaging reveals the atomic structure of as‐formed 1H and 1T ′ alloys. Unlike the commonly observed displacement of metal atoms in the 1T ′ phase, local displacement of Te atoms from original 1H lattice sites is discovered by combined STEM‐ADF imaging and ab initio molecular dynamics calculations. The structure distortion provides new insights into the structure formation of alloys. This generic synthetic approach is also demonstrated for other telluride‐based ternary monolayers such as WTe_2xSe_2(1?x) single crystals.     

Solution‐Processed 3D RGO–MoS2/Pyramid Si Heterojunction for Ultrahigh Detectivity and Ultra‐Broadband Photodetection

Molybdenum disulfide (MoS₂), a typical 2D metal dichalcogenide (2DMD), has exhibited tremendous potential in optoelectronic device applications, especially in photodetection. However, due to the weak light absorption of planar mono‐/multilayers, limited cutoff wavelength edge, and lack of high‐quality junctions, most reported MoS₂‐based photodetectors show undesirable performance. Here, a structurized 3D heterojunction of RGO–MoS₂/pyramid Si is demonstrated via a simple solution‐processing method. Owing to the improved light absorption by the pyramid structure, the narrowed bandgap of the MoS₂ by the imperfect crystallinity, and the enhanced charge separation/transportation by the inserted reduced graphene oxide (RGO), the assembled photodetector exhibits excellent performance in terms of a large responsivity of 21.8 A W^?1, extremely high detectivity up to 3.8 × 10¹⁵ Jones (Jones = cm Hz^1/2 W^?1) and ultrabroad spectrum response ranging from 350 nm (ultraviolet) to 4.3 µm (midwave infrared). These device parameters represent the best results for MoS₂‐based self‐driven photodetectors, and the detectivity value sets a new record for the 2DMD‐based photodetectors reported thus far. Prospectively, the design of novel 3D heterojunction can be extended to other 2DMDs, opening up the opportunities for a host of high‐performance optoelectronic devices.     

Symmetry‐Reduction Enhanced Polarization‐Sensitive Photodetection in Core–Shell SbI3/Sb2O3 van der Waals Heterostructure

Structural symmetry is a simple way to quantify the anisotropic properties of materials toward unique device applications including anisotropic transportation and polarization‐sensitive photodetection. The enhancement of anisotropy can be achieved by artificial symmetry‐reduction design. A core–shell SbI₃/Sb₂O₃ nanowire, a heterostructure bonded by van der Waals forces, is introduced as an example of enhancing the performance of polarization‐sensitive photodetectors via symmetry reduction. The structural, vibrational, and optical anisotropies of such core–shell nanostructures are systematically investigated. It is found that the anisotropic absorbance of a core–shell nanowire is obviously higher than that of two single compounds from both theoretical and experimental investigations. Anisotropic photocurrents of the polarization‐sensitive photodetectors based on these core–shell SbI₃/Sb₂O₃ van der Waals nanowires are measured ranging from ultraviolet (UV) to visible light (360–532 nm). Compared with other van der Waals 1D materials, low anisotropy ratio (I_max/I_min) is measured based on SbI₃ but a device based on this core–shell nanowire possesses a relatively high anisotropy ratio of ≈3.14 under 450 nm polarized light. This work shows that the low‐symmetrical core–shell van der Waals heterostructure has large potential to be applied in wide range polarization‐sensitive photodetectors.     

Controllable Synthesis of Atomically Thin Type‐II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All‐Solid‐State Flexible Supercapacitors

Compared with 2D S‐based and Se‐based transition metal dichalcogenides (TMDs), Te‐based TMDs display much better electrical conductivities, which will be beneficial to enhance the capacitances in supercapacitors. However, to date, the reports about the applications of Te‐based TMDs in supercapacitors are quite rare. Herein, the first supercapacitor example of the Te‐based TMD is reported: the type‐II Weyl semimetal 1Td WTe₂. It is demonstrated that single crystals of 1Td WTe₂ can be exfoliated into the nanosheets with 2–7 layers by liquid‐phase exfoliation, which are assembled into air‐stable films and further all‐solid‐state flexible supercapacitors. The resulting supercapacitors deliver a mass capacitance of 221 F g^?1 and a stack capacitance of 74 F cm^?3. Furthermore, they also show excellent volumetric energy and power densities of 0.01 Wh cm^?3 and 83.6 W cm^?3, respectively, superior to the commercial 4V/500 µAh Li thin‐film battery and the commercial 3V/300 µAh Al electrolytic capacitor, in association with outstanding mechanical flexibility and superior cycling stability (capacitance retention of ≈91% after 5500 cycles). These results indicate that the 1Td WTe₂ nanosheet is a promising flexible electrode material for high‐performance energy storage devices.     

Design for Highly Piezoelectric and Visible/Near‐Infrared Photoresponsive Perovskite Oxides

Defect‐engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B‐site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point‐defect‐mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect‐induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni²⁺‐mediated (1–x)Na_0.5Bi_0.5TiO₃‐xBa(Ti_0.5Ni_0.5)O_3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near‐infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d₃₃ = 151 pC N^–1, Pr = 31.2 μC cm^–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O₃. This research provides a new paradigm for designing highly piezoelectric and visible/near‐infrared photoresponsive perovskite oxides for solar energy conversion, near‐infrared detection, and other multifunctional applications.     

Self‐Confined Growth of Ultrathin 2D Nonlayered Wide‐Bandgap Semiconductor CuBr Flakes

2D planar structures of nonlayered wide‐bandgap semiconductors enable distinguished electronic properties, desirable short wavelength emission, and facile construction of 2D heterojunction without lattice match. However, the growth of ultrathin 2D nonlayered materials is limited by their strong covalent bonded nature. Herein, the synthesis of ultrathin 2D nonlayered CuBr nanosheets with a thickness of about 0.91 nm and an edge size of 45 µm via a controllable self‐confined chemical vapor deposition method is described. The enhanced spin‐triplet exciton (Z_f, 2.98 eV) luminescence and polarization‐enhanced second‐harmonic generation based on the 2D CuBr flakes demonstrate the potential of short‐wavelength luminescent applications. Solar‐blind and self‐driven ultraviolet (UV) photodetectors based on the as‐synthesized 2D CuBr flakes exhibit a high photoresponsivity of 3.17 A W^?1, an external quantum efficiency of 1126%, and a detectivity (D*) of 1.4 × 10¹¹ Jones, accompanied by a fast rise time of 32 ms and a decay time of 48 ms. The unique nonlayered structure and novel optical properties of the 2D CuBr flakes, together with their controllable growth, make them a highly promising candidate for future applications in short‐wavelength light‐emitting devices, nonlinear optical devices, and UV photodetectors.     

Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

To achieve excellent photoelectrochemical water‐splitting activity, photoanode materials with high light absorption and good charge‐separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO₃ (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen‐vacancy concentration (8.7%) exhibits high light‐absorption and good charge‐separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm^?2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm^?2 and stable gas production with an average solar‐to‐hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water‐splitting system.     

Black Phosphorus Revisited: A Missing Metal‐Free Elemental Photocatalyst for Visible Light Hydrogen Evolution

Metal‐free elemental photocatalysts for hydrogen (H₂) evolution are more advantageous than the traditional metal‐based inorganic photocatalysts since the nonmetal elements are generally cheaper, more earth‐abundant, and environmentally friendly. Black phosphorus (BP) has been attracting increasing attention in recent years based on its anisotropic 2D layered structure with tunable bandgap in the range of 0.3–2.0 eV; however, the application of BP for photocatalytic H₂ evolution has been scarcely reported experimentally although being theoretically predicted. Herein, for the first time, the visible light photocatalytic H₂ evolution of BP nanosheets prepared via a facile solid‐state mechanochemical method by ball‐milling bulk BP is reported. Without using any noble metal cocatalyst, the visible light photocatalytic hydrogen evolution rate of BP nanosheets reaches 512 µmol h^?1 g^?1, which is ≈18 times higher than that of the bulk BP, and is comparable or even higher than that of graphitic carbon nitrides (g‐C₃N₄).     

Ultrafast Orbital‐Oriented Control of Magnetization in Half‐Metallic La0.7Sr0.3MnO3 Films

Manipulating spins by ultrafast pulse laser provides a new avenue to switch the magnetization for spintronic applications. While the spin–orbit coupling is known to play a pivotal role in the ultrafast laser‐induced demagnetization, the effect of the anisotropic spin–orbit coupling on the transient magnetization remains an open issue. This study uncovers the role of anisotropic spin–orbit coupling in the spin dynamics in a half‐metallic La_0.7Sr_0.3MnO₃ film by ultrafast pump–probe technique. The magnetic order is found to be transiently enhanced or attenuated within the initial sub‐picosecond when the probe light is tuned to be s‐ or p‐polarized, respectively. The subsequent slow demagnetization amplitude follows the fourfold symmetry of the ${\mathrm{d}}_{x^2?y^2}$ orbitals as a function of the polarization angles of the probe light. A model based on the Elliott–Yafet spin‐flip scatterings is proposed to reveal that the transient magnetization enhancement is related to the spin‐mixed states arising from the anisotropic spin–orbit coupling. The findings provide new insights into the spin dynamics in magnetic systems with anisotropic spin–orbit coupling as well as perspectives for the ultrafast control of information process in spintronic devices.     

High‐Performance,Room Temperature,Ultra‐Broadband Photodetectors Based on Air‐Stable PdSe2

Photodetection over a broad spectral range is crucial for optoelectronic applications such as sensing, imaging, and communication. Herein, a high‐performance ultra‐broadband photodetector based on PdSe₂ with unique pentagonal atomic structure is reported. The photodetector responds from visible to mid‐infrared range (up to ≈4.05 µm), and operates stably in ambient and at room temperature. It promises improved applications compared to conventional mid‐infrared photodetectors. The highest responsivity and external quantum efficiency achieved are 708 A W^?1 and 82 700%, respectively, at the wavelength of 1064 nm. Efficient optical absorption beyond 8 µm is observed, indicating that the photodetection range can extend to longer than 4.05 µm. Owing to the low crystalline symmetry of layered PdSe₂, anisotropic properties of the photodetectors are observed. This emerging material shows potential for future infrared optoelectronics and novel devices in which anisotropic properties are desirable.     

PtTe2‐Based Type‐II Dirac Semimetal and Its van der Waals Heterostructure for Sensitive Room Temperature Terahertz Photodetection

Recent years have witnessed rapid progresses made in the photoelectric performance of two‐dimensional materials represented by graphene, black phosphorus, and transition metal dichalcogenides. Despite significant efforts, a photodetection technique capable for longer wavelength, higher working temperature as well as fast responsivity, is still facing huge challenges due to a lack of best among bandgap, dark current, and absorption ability. Exploring topological materials with nontrivial band transport leads to peculiar properties of quantized phenomena such as chiral anomaly, and magnetic‐optical effect, which enables a novel feasibility for an advanced optoelectronic device working at longer wavelength. In this work, the direct generation of photocurrent at low energy terahertz (THz) band at room temperature is implemented in a planar metal–PtTe₂–metal structure. The results show that the THz photodetector based on PtTe₂ with bow‐tie‐type planar contacts possesses a high photoresponsivity (1.6 A W^?1 without bias voltage) with a response time less than 20 µs, while the PtTe₂–graphene heterostructure‐based detector can reach responsivity above 1.4 kV W^?1 and a response time shorter than 9 µs. Remarkably, it is already exploitable for large area imaging applications. These results suggest that topological semimetals such as PtTe₂ can be ideal materials for implementation in a high‐performing photodetection system at THz band.     

Poly(1,4‐Diethynylbenzene) Gradient Homojunction with Enhanced Charge Carrier Separation for Photoelectrochemical Water Reduction

As appealing photoelectrode materials for photoeletrochemical hydrogen evolution reaction (PEC HER), conjugated polymers still show poor PEC HER performance as a result of their serious recombination of photogenerated electrons and holes. Herein, a novel design of gradient homojunction is demonstrated by controlled copolymerization of 1,4‐diethynylbenzene (DEB) and 1,3,5‐triethynylbenzene (TEB). The as‐built gradient distribution of TEB monomer in poly(1,4‐diethynylbenzene) (pDEB) leads to continuous band bending engineering, which constitutes a gradient homojunction. Under AM 1.5G irradiation and in 0.1 m Na₂SO₄ aqueous solution, the as‐fabricated pDEB gradient homojunction exhibits a charge separation efficiency of 0.27% at 0.3 V versus reversible hydrogen electrode (RHE), which is 3.4 and 1.7 times higher than those for pure pDEB and the traditionally designed pDEB homojunction. As a result, the photocurrent of the pDEB gradient homojunction unprecedentedly reaches 55 µA cm^?2 at 0.3 V versus RHE, which is much higher than 19 µA cm^?2 for pure pDEB, 32 µA cm^?2 for the pDEB homojunction, and state‐of‐the‐art organic photocathodes, e.g., g‐C₃N₄ (≈1?32 µA cm^?2). This work opens up a new window for the design of gradient homojunctions and will advance the exploration of high‐performance organic photoelectrodes.     

Hierarchical Porous O‐Doped g‐C3N4 with Enhanced Photocatalytic CO2 Reduction Activity

Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO₂ is considered as a potential route for solving ever‐increasing energy crisis and greenhouse effect. Herein, hierarchical porous O‐doped graphitic carbon nitride (g‐C₃N₄) nanotubes (OCN‐Tube) are prepared via successive thermal oxidation exfoliation and curling‐condensation of bulk g‐C₃N₄. The as‐prepared OCN‐Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20–30 nm. The hierarchical OCN‐Tube shows excellent photocatalytic CO₂ reduction performance under visible light, with methanol evolution rate of 0.88 µmol g^?1 h^?1, which is five times higher than bulk g‐C₃N₄ (0.17 µmol g^?1 h^?1). The enhanced photocatalytic activity of OCN‐Tube is ascribed to the hierarchical nanotube structure and O‐doping effect. The hierarchical nanotube structure endows OCN‐Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O‐doping optimizes the band structure of g‐C₃N₄, resulting in narrower bandgap, greater CO₂ affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g‐C₃N₄ nanostructures, which can be used as promising photocatalyst for solar energy conversion.     

Nonlinear Saturable Absorption of Liquid‐Exfoliated Molybdenum/Tungsten Ditelluride Nanosheets

Molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS₂ and WS₂, molybdenum ditelluride (MoTe₂) and tungsten ditelluride (WTe₂) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near‐infrared wavelength regime. Here, few‐layer MoTe₂/WTe₂ nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe₂/WTe₂ nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode‐locking operations are realized separately in erbium‐doped fiber lasers utilizing two types of MoTe₂/WTe₂‐based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe₂/WTe₂ nanosheets, such as visible/near‐infrared pulsed laser, materials processing, optical sensors, and modulators.     

MXene‐Derived Ferroelectric Crystals

This study demonstrates the first synthesis of MXene‐derived ferroelectric crystals. Specifically, high‐aspect‐ratio potassium niobate (KNbO₃) ferroelectric crystals is successfully synthesized using 2D Nb₂C, MXene, and potassium hydroxide (KOH) as the niobium and potassium source, respectively. Material analysis confirms that a KNbO₃ orthorhombic phase with Amm2 symmetry is obtained. Additionally, ferroelectricity in KNbO₃ is confirmed using standard ferroelectric, dielectric, and piezoresponse force microscopy measurements. The KNbO₃ crystals exhibit a saturated polarization of ≈21 µC cm^?2, a remnant polarization of ≈17 µC cm^?2, and a coercive field of ≈50 kV cm^?1. This discovery illustrates that the 2D nature of MXenes can be exploited to grow ferroelectric crystals.     

In‐Plane Anisotropic Thermal Conductivity of Few‐Layered Transition Metal Dichalcogenide Td‐WTe2

2D Td‐WTe₂ has attracted increasing attention due to its promising applications in spintronic, field‐effect chiral, and high‐efficiency thermoelectric devices. It is known that thermal conductivity plays a crucial role in condensed matter devices, especially in 2D systems where phonons, electrons, and magnons are highly confined and coupled. This work reports the first experimental evidence of in‐plane anisotropic thermal conductivities in suspended Td‐WTe₂ samples of different thicknesses, and is also the first demonstration of such anisotropy in 2D transition metal dichalcogenides. The results reveal an obvious anisotropy in the thermal conductivities between the zigzag and armchair axes. The theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in stronger anisotropy. The findings here are crucial for developing efficient thermal management schemes when engineering thermal‐related applications of a 2D system.