Anisotropic Transport Properties Research Articles

Piperidine and Pyridine Series Lead-Free Dion-Jacobson Phase Tin Perovskite Single Crystals and Their Applications for Field-Effect Transistors.

Two-dimensional (2D) organic-inorganic metal halide perovskites have gained immense attention as alternatives to three-dimensional (3D) perovskites in recent years. The hydrophobic spacers in the layered structure of 2D perovskites make them more moisture-resistant than 3D perovskites. Moreover, they exhibit unique anisotropic electrical transport properties due to a structural confinement effect. In this study, four lead-free Dion-Jacobson (DJ) Sn-based phase perovskite single crystals, 3AMPSnI4, 4AMPSnI4, 3AMPYSnI4, and 4AMPYSnI4 [AMP = (aminomethyl)-piperidinium, AMPY = (aminomethyl)pyridinium] are reported. Results reveal structural differences between them impacting the resulting optical properties. Namely, higher octahedron distortion results in a higher absorption edge. Density functional theory (DFT) is also performed to determine the trends in energy band diagrams, exciton binding energies, and formation energies due to structural differences among the four single crystals. Finally, a field-effect transistor (FET) based on 4AMPSnI4 is demonstrated with a respectable hole mobility of 0.57 cm2 V-1 s-1 requiring a low threshold voltage of only -2.5 V at a drain voltage of -40 V. To the best of our knowledge, this is the third DJ-phase perovskite FET reported to date.

Strong anisotropic transport properties of quasi-one-dimensional ZrTe3 nanoribbons

Transition metal trichalcogenides (TMTCs) with quasi-one-dimensional (quasi-1D) structures have attracted extensive interest in diverse fields because of their unique electronic properties. Herein, we report strong in-plane anisotropic transport properties of ZrTe3 nanoribbons, which originate from their quasi-1D structures. ZrTe3 nanoribbons were mechanically exfoliated from bulk single crystals, and transport properties, including electrical conductivity (σ) and Seebeck coefficient (S), were measured in the longitudinal and transverse directions of the rectangular nanoribbons. σ was higher in the transverse direction than that in the longitudinal direction. S measurement revealed further clear anisotropic characteristics, and positive and negative S values were obtained in the longitudinal and transverse directions, respectively. Furthermore, a significant change in the transport properties was observed with a post treatment, and the potential of ZrTe3 for transport property modulation was confirmed. We believe that our findings will contribute to the understanding of anisotropic transport in quasi-1D ZrTe3 and expansion of the application fields of quasi-1D ZrTe3.

Boosting the thermoelectric properties of layered SnSb2Te4 compound by microstructure regulation combined with heterovalent halogen substitution

The layered IVV2Te4-based compounds have recently received significant attention due to their intrinsically low lattice thermal conductivities. However, the influence of microstructure regulation and halogen doping on their thermoelectric properties has been scarcely studied. In this work, we systematically investigated the anisotropic thermoelectric transport properties of pristine SnSb2Te4 compounds with varied microstructures manipulated by ball milling. With the help of thermoelectric transport models, the optimal ball milling time is estimated based on the calculation of quality factor. Furthermore, the remarkably improved Seebeck coefficient is achieved by the introduction of halogen elements into Te sites, which is attributed to reduced carrier concentration and converged carrier pockets. As a result, a maximal zT ∼0.4 at 725 K is achieved in SnSb2(Te0·94I0.06)4 sample aligned with the SPS pressure direction with a ball-milling time of 1 h, which demonstrates a 35 % enhancement over the pristine sample. This work provides an insightful guide to elevate the thermoelectric properties of layered IVVI2Te4-based compounds.

Unraveling High Thermal Conductivity with In-Plane Anisotropy Observed in Suspended SiP2.

The anisotropic thermal transport properties of low-symmetry two-dimensional materials play an important role in understanding heat dissipation and optimizing thermal management in integrated devices. Examples of efficient energy dissipation and enhanced power sustainability have been demonstrated in nanodevices based on materials with anisotropic thermal transport properties. However, the exploration of materials with high thermal conductivity and strong in-plane anisotropy remains challenging. Herein, we demonstrate the observation of anisotropic in-plane thermal conductivities of few-layer SiP2 based on the micro-Raman thermometry method. For suspended SiP2 nanoflake, the thermal conductivity parallel to P-P chain direction (κ∥b) can reach 131 W m-1 K-1 and perpendicular to P-P chain direction (κ⊥b) is 89 W m-1 K-1 at room temperature, resulting in a significant anisotropic ratio (κ∥b/κ⊥b) of 1.47. Note that such a large anisotropic ratio mainly results from the higher phonon group velocity along the P-P chain direction. We also found that the thermal conductivity can be effectively modulated by increasing the SiP2 thickness, reaching a value as high as 202 W m-1 K-1 (120 W m-1 K-1) for κ∥b (κ⊥b) at 111 nm thickness, which is the highest among layered anisotropic phosphide materials. Notably, the anisotropic ratio always remains at a high level between 1.47 and 1.68, regardless of the variation of SiP2 thickness. Our observation provides a new platform to verify the fundamental theory of thermal transport and a crucial guidance for designing efficient thermal management schemes of anisotropic electronic devices.

The anisotropic transport properties of the three-terminal ballistic junction based on α−T 3 lattice

The three-terminal ballistic junction (TBJ) has promising applications in nanoelectronics. We investigate the transport properties of a α−T 3-based TBJ, where two typical configurations are considered, i.e. the A- and Z-TBJ. It is found that both A- and Z-TBJ exhibit transmission anisotropy, and the transmission of the A-TBJ has stronger anisotropy than that of the Z-TBJ. The amplitude of the rectification coefficient is smaller than that of phosphorene TBJ, but larger than that of graphene TBJ. When the symmetrical input is applied, the output voltage curve exhibits symmetric behavior. While in the case of asymmetric input, the symmetric behavior is broken, and the maximum value of the output voltage can reach a positive value. Interestingly, the voltage output shows a dramatic nonlinear response which may be useful for the voltage diode application with a push-pull input voltage. In addition, the heat fluxes of the asymmetric input are much smaller than those of the symmetric input. The maximum value of the heat flux under the symmetric input exceeds twice of that under the asymmetric input. Our results are useful to design nanoelectronic devices based on α−T 3 TBJ.

First-Principles Investigation of Simultaneous Thermoelectric Power Generation and Active Cooling in a Bifunctional Semimetal ZrSeTe Janus Structure.

Traditional thermoelectric materials often face a trade-off between efficient power generation (high ZT) and cooling performance. Here, we explore the potential of achieving simultaneous thermoelectric power generation and cooling capability in the recently fabricated bulk ZrSeTe Janus structure using first-principles density functional theory (DFT). The layered ZrSeTe Janus structure exhibits a semimetal character with anisotropic transport properties along the in-plane and out-of-plane directions. Our DFT calculations, including the explicit calculation of relaxation time, reveal a maximum ZT of ~0.065 in the out-of-plane direction at 300 K which is one order of magnitude larger than that in the in-plane direction (ZT~0.006). Furthermore, the thermoelectric cooling performance is also investigated. The in-plane direction shows a cooling performance of 13 W/m·K and a coefficient of performance (COPmax) of ~90 with a temperature difference (ΔT) of 30 K, while the out-of-plane direction has a cooling performance of 2.5 W/m·K and COPmax of ~2.5. Thus, the out-of-plane current from the thermoelectric power generation can be utilized as an in-plane current source for active heat pumping. Consequently, we propose that the semimetal ZrSeTe Janus structure can display bifunctional thermoelectric properties for simultaneous thermoelectric power generation and active cooling.

Transport properties evaluation of pore-scale GDLs for PEMFC using orthogonal design method

Gas diffusion layer (GDL) is an essential component of proton exchange membrane fuel cells, serving the functions of gas-water transport, thermal-electrical conduction and mechanical support. The various microstructural characteristics of the GDL have coupled and complex impact on transport properties, which is not comprehensively considered in previous studies. This study combines stochastically reconstruction techniques, pore-scale modeling and orthogonal design method to evaluate the coupling effect of multiple microstructural characteristics on transport properties, and determine the impact degree of each microstructural characteristics, including fiber diameter, porosity, GDL thickness, fiber orientation coefficient, binder and PTFE content. Finally, new mathematical models are developed and validated to predict and optimize the anisotropic transport properties accurately and rapidly by considering the coupling effect of multiple microstructural characteristics. The results showed that porosity has higher impact degree on gas diffusion and heat conduction than other microstructural characteristics. The combinations of microstructural parameters are optimized to achieve higher performance, with thermal conductivity and gas diffusivity increased by ≥139% and 62%, respectively. The prediction mathematical models are validated with the error ranging from 1% to 8%, which can predict transport properties and optimize the GDL microstructure accurately and rapidly.

Effect of vacancy defects on anisotropic electronic transport behaviors of CoN4C2 based 2D devices: a first-principles study

The strong anisotropic electronic transport properties of the single-atom-thick material CoN4C2 monolayer hold immense importance for the advancement of the electronics industry. Using density functional theory combined with non-equilibrium Green’s function systematically studied the electronic structural properties and anisotropic electronic transport properties of the CoN4C2 monolayer. The results show that Co, N, and C single-atom vacancy defects do not change the electronic properties of the CoN4C2 monolayer, which remains metallic. The pristine device and the devices composed of Co, N single-atom vacancy defects exhibit stronger electronic transport along the armchair direction than the zigzag direction, which exhibit strong anisotropy, and a negative differential resistance (NDR) effect can be observed. In contrast to the results mentioned above, the device with C single-atom vacancy defects only exhibits the NDR effect. Among them, the device with the N single-atom vacancy defect regime exhibits the strongest anisotropy, with an I Z/I A of up to 7.95. Moreover, based on the strongest anisotropy exhibited by N single-atom vacancy defects, we further studied the influence of different sites of the N-atom vacancy on the electronic transport properties of the devices. The results indicate that N-1, N-2, N-3, N-12, N-23, N-123, N-1234, and N-12345 model devices did not change the high anisotropy and NDR effect of the device, and among them the N-1234 exhibits the strongest anisotropy, the I Z/I A reaches 6.12. A significant NDR effect is also observed for the electronic transport along the armchair direction in these devices. However, the current gradually decreases as an increase of the number of N defects. These findings showcase the considerable potential for integration of the CoN4C2 monolayer in switching devices and NDR-based multifunctional nanodevices.

Origin of the Anomalous Electrical Transports in Quasi-One-Dimensional Ta2NiSe7.

Exploration of exotic transport behavior is of great interest and importance for revealing the properties of the CDW phase of quasi-one-dimensional Ta2NiSe7. We report the anisotropic electrical transport properties of Ta2NiSe7 single crystals in the CDW phase. The anisotropic constant (γ = ρb/ρc) increased rapidly at TCDW = 60 K upon cooling. The results of the Hall resistivity show that both the concentrations and mobilities of carriers change abruptly at TCDW. The out-of-plane AMR exhibits C2 and C4 symmetry components while the in-plane AMR exhibits C2, C4, and C6 at the CDW state. The planar Hall effect is observed in Ta2NiSe7 at low temperature, which is suggested to originate from the anisotropic orbital magnetoresistance. The calculated results show that the Fermi surface of Ta2NiSe7 was slightly reconstructed due to the CDW transition. This work highlights the enhancement of Fermi surface anisotropy during CDW formation and provides a novel approach to study the CDW materials.

Anisotropic and High‐Mobility Electronic Transport in a Quasi 2D Antiferromagnet NdSb2

AbstractAdvancements in low‐dimensional functional device technology heavily rely on the discovery of suitable materials which have interesting physical properties as well as can be exfoliated down to the 2D limit. Exfoliable high‐mobility magnets are one such class of materials that, not due to lack of effort, has been limited to only a handful of options. So far, most of the attention has been focused on the van der Waals (vdW) systems. However, even within the non‐vdW, layered materials, it is possible to find all these desirable features. Using chemical reasoning, it is found that NdSb2 is an ideal example. Even with a relatively small interlayer distance, this material can be exfoliated down to few layers. NdSb2 has an antiferromagnetic ground state with a quasi 2D spin arrangement. The bulk crystals show a very large, non‐saturating magnetoresistance along with highly anisotropic electronic transport properties. It is confirmed that this anisotropy originates from the 2D Fermi pockets which also imply a rather quasi 2D confinement of the charge carrier density. Both electron and hole‐type carriers show very high mobilities. The possible non‐collinear spin arrangement also results in an anomalous Hall effect.

In situ self-assembled NdBa0.5Sr0.5Co2O5+δ/Gd0.1Ce0.9O2-δ hetero-interfaces enable enhanced electrochemical activity and CO2 durability for solid oxide fuel cells

The development of solid oxide fuel cells (SOFCs) faces impediments in terms of challenges associated with oxygen reduction activity and CO2 durability. Therefore, a series of novel composite cathode materials, consisting of NdBa0.5Sr0.5Co2O5+δ (NBSC) and Gd0.1Ce0.9O2-δ (GDC), were designed and synthesized using a one-pot strategy through a self-assembly process. The incorporation of GDC leads to a significant increase in the number of active sites. Furthermore, it alters the anisotropic transport properties of oxygen ions within layered double perovskite materials, consequently creating a three-dimensional conduit for O2– transportation. Simultaneously, the in-situ formation of closely intertwined heterogeneous interfaces between NBSC and GDC particles can facilitate the charge transfer processes and oxygen ion transport, thereby improving the kinetics of the oxygen reduction reaction (ORR). The NBSC-10GDC cathode, prepared through the one-pot method, exhibits reduced polarization resistances and enhanced CO2 tolerance in comparison to the mechanically mixed cathode. At 750 °C, the one-pot NBSC-10GDC exhibits a low area-specific resistance (ASR) of 0.029 Ω cm2, which is 69.8% lower than the ASR of single-phase NBSC and 42.0% lower than mechanically mixed NBSC-10GDC. Additionally, the one-pot NBSC-10GDC demonstrates a remarkable maximum power density (MPD) of 1.36 W cm−2 at 750 °C. These findings highlight the considerable potential of the one-pot NBSC-10GDC as a promising material for SOFC cathode.

Graphenization of graphene oxide films for strongly anisotropic thermal conduction and high electromagnetic interference shielding

A macroscopic carbon film that has a “graphenic” structure (defect-free in-plane graphene lattice yet absence of Bernal type graphitic stacking order), may inherit the exotic properties of rotated/slipped few-layer graphene (e.g., high flexibility and anisotropic transport properties). However, the fabrication of such a film remains challenging and unreported. Here we show that the annealing of reduced electrochemical graphene oxide (REGO), which has fewer in-plane defects than the conventional graphene oxide from Hummers’ method, leads to a nearly intact graphene lattice (Raman ID/IG down to 0.03) without restoring the graphitic stacking order (I2D/IG > 1 and a single Lorentzian 2D peak). Atomic resolution transmission electron microscopy verifies the unique graphenic structure with random interlayer rotations. Density functional theory calculations imply the low defect density of REGO can suppress the interplanar interaction between undercoordinated carbon atoms, therefore inhibiting cross-plane migration of vacancies and the consequent establishment of stacking order. The annealed, graphenic REGO film is highly flexible and has an in-plane to cross-plane thermal conductivity ratio of 835 (among the highest reported for anisotropic thermal conductors). This high anisotropic ratio is attributed to the inhibited through-plane heat transport (0.26 W m−1 K−1) by the interlayer rotations and the high in-plane thermal conductivity (218 W m−1 K−1) enabled by intact graphene lattice. The graphenic films show high electromagnetic interference shielding effectiveness of 80.3 dB at a thickness of 53 μm and 42.4 dB at 5.7 μm, with an absolute effectiveness (>70000 dB cm2 g−1) superior to two-dimensional metal carbides (MXenes) and Al foil.

Electronic and optical characteristics of Silicane/GeAs van der Waals heterostructures: Effects of external electric field and biaxial strain: A first-principles study

The van der Waals heterostructure offers unusual physical properties to design novel structures for efficient optoelectronic applications. To enhance the low mobility of monolayer SiH and broaden the light absorption coefficient and range of monolayer SiH, a lattice-matched SiH/GeAs vdWh has been constructed. At the same time, the basic electronic and optical properties were investigated by first-principles calculations. The SiH/GeAs vdWh with six different structural configurations were compared, and the most stable configuration model H2 has a type-II band alignment with an indirect bandgap semiconductor value of 1.54 eV. It is associated with a strong charge transfer. Moreover, SiH/GeAs vdWh possesses anisotropic transport properties with high electron mobility along the y-direction. Interestingly, both external electric field and biaxial strain can adjust band offsets and bandgaps values. After applying vertical electric fields, The SiH/GeAs vdWh has a mutual transformation from type-I (symmetric) to type-II(staggered) to type-III(broken) band alignment, and metal-semiconductor phase transitions occurred at −0.35 and 0.15 V/Å. Besides, it's found that band alignment transition from type-II to type-I emerged under the in-plane biaxial strain of 2% and transformed indirect into direct bandgap. More importantly, tensile biaxial strain can enhance the visible-light absorption while sustaining type-II band alignment, which is favorable for photocatalysis of visible light. Our results indicate that the SiH/GeAs vdWh's moderate bandgap, excellent transport properties and optical performance may have potential applications in the field of nanoelectronic and optoelectronic devices.

A Comparative Study of the Electronic Transport and Gas-Sensitive Properties of Graphene+, T-graphene, Net-graphene, and Biphenylene-Based Two-Dimensional Devices.

The electronic transport properties of the four carbon isomers: graphene+, T-graphene, net-graphene, and biphenylene, as well as the gas-sensing properties to the nitrogen-based gas molecules including NO2, NO, and NH3 molecules, are systematically studied and comparatively analyzed by combining the density functional theory with the nonequilibrium Green's function. The four carbon isomers are metallic, especially with graphene+ being a Dirac metal due to the two Dirac cones present at the Fermi energy level. The two-dimensional devices based on these four carbon isomers exhibit good conduction properties in the order of biphenylene > T-graphene > graphene+ > net-graphene. More interestingly, net-graphene-based and biphenylene-based devices demonstrate significant anisotropic transport properties. The gas sensors based on the above four structures all have good selectivity and sensitivity to the NO2 molecule, among which T-graphene-based gas sensors are the most prominent with a maximum ΔI value of 39.98 μA, being only three-fifths of the original. In addition, graphene+-based and biphenylene-based gas sensors are also sensitive to the NO molecule with maximum ΔI values of 29.42 and 25.63 μA, respectively. However, the four gas sensors are all physically adsorbed for the NH3 molecule. By the adsorption energy, charge transfer, electron localization functions, and molecular projection of self-consistent Hamiltonian states, the mechanisms behind all properties can be clearly explained. This work shows the potential of graphene+, T-graphene, net-graphene, and biphenylene for the detection of toxic molecules of NO and NO2.

Evaluation of the electronic properties of layered TlPbI3 perovskites

TlPbI3 is a new three-dimensional layered halide perovskite with special optoelectronic properties. Simulations of unique geometric and electronic structures showed that in contrast to ordinary halide perovskites, the Tl ion orbitals significantly contribute to the bonding interactions. We simulated the low-temperature changes in the TlPbI3 lattice by contracting the lattice constant and found that the bond angles decreased with lattice shrinkage, which reveals a significant lateral displacement between the atoms in the TlPbI3 crystal; this leads to reinforced bonding interactions between Tl, Pb, and I ions. Stronger bonding interactions generate more dispersive band edges, thereby increasing the bandwidth and reducing the bandgap. Moreover, the enhanced dispersion of the band edges resulted in reduced effective carrier masses and anisotropic transport properties. This provides a strategy for modulating the physical performance of new perovskites.

Anisotropic transport properties and high-mobility of charge carriers of antiferromagnetic GdAgSb2

We report detailed magnetic and magnetotransport properties of single-crystalline GdAgSb2 antiferromagnet. The electronic transport properties show metallic behavior along with large, anisotropic, and non-saturating magnetoresistance (MR) in transverse experimental configuration. At 2 K and 9 T, the value of MR reaches as high as ∼1.8×103%. The anisotropic MR along with additional features for applied magnetic field along some specific crystallographic directions reveal the quasi-two-dimensional nature of the Fermi surface of GdAgSb2. Hall resistivity confirms the presence of two types of charge carriers. The high carrier mobilities (∼1.2×104 cm2 V−1 s−1) and nearly-compensated electron and hole-density (∼1019 cm−3) could be responsible for the large transverse MR in GdAgSb2. We have also observed the de Haas–van Alphen oscillations in the magnetization measurements below 7 K. Furthermore, the robust planar Hall effect, which persists up to high temperatures, could indicate the nontrivial nature of the electronic band structure for GdAgSb2.

Promising anisotropic mechanical, electronic, and charge transport properties of 2D InN alloys for photocatalytic water splitting

Two-dimensional (2D) materials with unique physical properties lead to new possibilities in future nanomaterial-based devices. Among them, 2D structures suitable to be the solar-driven catalyst for water-splitting reactions have become excessively important since the demand for clean energy sources has increased. Apart from the conventional crystals with well-known symmetries, recent studies showed that materials with exotic decorations could possess superior features in these kinds of applications. In this respect, we report novel 2D tetrahexagonal (th-) InN crystal and its ordered alloys In0.33X0.67N (X=Al, Ga) that can be utilized as effective catalysts for water splitting reactions. Proposed structures possess robust energetic, dynamical, thermal, and mechanical stability with a versatile mechanical response. After a critical tensile strain value, all monolayers exhibit strain-induced negative Poisson’s ratio in a particular crystal direction, making them half-auxetic materials. The examined materials are indirect semiconductors with desired band gaps and band edge positions for water-splitting applications. Due to their structural anisotropy, they have direction-dependent mobility that can keep the photogenerated charge carriers separated by reducing their recombination probability, which boosts the photocatalytic process. High absorption capacity in the wide spectral range underlines their potential performance. The versatile mechanical, electronic, and optical properties of 2D th-InN and its alloys, together with their remarkable structural stability, indicate that they can appropriately be exploited in the future for water splitting applications.

Unravelling the regulating role of strain engineering on the phonon dispersion, mechanical behavior, and electronic transport properties of pentagonal PtTe2 monolayer

Inspired by the experimental synthesis of PdSe2 monolayer with a novel buckling configuration, the mechanical property, phonon dispersion curve, electronic structure, and carrier mobility of anisotropic pentagonal PtTe2 monolayer under strain engineering are systematically investigated by first-principles calculations and deformation potential (DP) theory. Ab initio molecular dynamics (AIMD) simulations show that the pentagonal PtTe2 monolayer is thermally stable at 300 and 600 K. Further phonon dispersion investigation verifies the dynamic stability of pentagonal PtTe2 monolayer under tensile strain, as evidenced by the absence of imaginary frequency. When subjected to tensile strains ranging from 2% to 4% in uniaxial (a- and b-direction) and biaxial directions, the mechanical properties and electronic band structures of pentagonal PtTe2 monolayer exhibit significant changes, leading to the electronic band convergence and decreasing bandgap. The effective mass, elastic constant, deformation potential, and carrier mobility also vary considerably under tensile strains, and a high hole mobility of 3618.51 cm2/V·s is discovered along the a-direction with 3% strain applied in the y-axis. Specifically, the hole mobility of pentagonal PtTe2 monolayer shows large anisotropy ratio, reaching up to 13.99 under 2% tensile strain in the y-axis. Our current work not only unravels the fundamental understanding of the anisotropic mechanical properties, phonon dispersion and electronic transport properties of pentagonal PtTe2 monolayer under strain engineering, but also provides theoretical guidance for applying strain engineering to tune the unique physical properties of two-dimensional materials with pentagonal configurations.

Hydrogenation-induced ultrahigh stabilization and tunable electronic structures of two-dimensional orthorhombic diboron diphosphide

Using density-functional theory calculations, we have studied hydrogenated two-dimensional (2D) orthorhombic diboron diphosphorus (O-B2P2). It is found that hydrogenation can transit the pristine O-B2P2 from a tiny bandgap semiconductor to a wide- and indirect-bandgap semiconductor, and the bandgaps are dependent on hydrogenation configurations. Moreover, our calculations have revealed that the three hydrogenated O-B2P2 nanostructures are both dynamically and thermally stable, and their bandgaps are estimated to be 2.8–4.2 eV according to hybrid potential calculations. They are predicted to possess strongly anisotropic mechanical and carrier transport properties, allowing potential applications for in-plane anisotropic and high-performance electronic devices. Hydrogenated O-B2P2 nanostructures exhibit strong absorbance of ultraviolet light and their bandgaps can be linearly modulated by tensile strain. Our findings demonstrate novel mechanical and electronic properties of hydrogenated O-B2P2 nanostructures, combined with excellent stability in ambient conditions, suggesting that they could be promising candidates for strongly anisotropic electronic and sensor devices.

In-doping induced resonant level and thermoelectric performance enhancement in n-type GeBi2Te4 single crystals with intrinsically low lattice thermal conductivity

Resonant level, the impurity level located inside the valence/conduction band, is an effective strategy for decoupling the electrical conductivity and Seebeck coefficient and enhancing the thermoelectric power factor. In this work, we show that In doping induces resonant level and enhances the thermoelectric performance of GeBi2Te4, a promising n-type thermoelectric material with layered structure. Single crystals grown by Bridgman method were used in this study to take the advantage of its anisotropic transport properties. An ultralow lattice thermal conductivity of ∼0.51 W m−1 K−1 at 323 K was found along the c-axis of GeBi2Te4, driven by intrinsic cation disorder and the low phonon group velocity from the relatively weak chemical bonds as well as the strong lattice anharmonicity caused by hierarchical bond orders. Both enhanced electrical conductivity and Seebeck coefficient were observed in the In-doped samples, indicating that In-doping not only increases the carrier concentration, but also introduces the resonant level that was further confirmed by the first-principles calculation. A maximum zT of ∼0.42 at 523 K and an average zT of 0.36 over 323 to 573 K were achieved in Ge0.97In0.03Bi2Te4 crystal sample, ∼100% and ∼89% enhancement compared to those of pristine single crystal sample, respectively. This study demonstrates another example of resonant level for thermoelectric performance enhancement, which may be applied to other related materials.