Small Band Gap Research Articles

Vacancy and strain effects on electronic structures of monolayer hexagonal 1T-phase pdSe2

Two-dimensional transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have traditionally been used, but Group-10 TMDs have recently attracted attention due to their small and tunable band gap and high mobility. This paper investigates the impact of vacancy and strain on the structure of hexagonal single-layer PdSe2 using density functional theory (DFT) calculations. The sublayers can introduce strain into the structure when building these 2D surfaces. Structures with chalcogen vacancies are more stable than those with metallic vacancies. When Se atoms are removed, the band gap disappears, and the semiconductor phase changes from semiconductor to conductor. The band gap can be recreated by applying a suitable percentage of strain using the vacancy mode. The work function (WF) was also calculated. WF decreases with compressive strain but increases with Se removal and tensile strain.

22% Record Efficiency in Nanorod Light-Emitting Diodes Achieved by Gradient Shells.

The external quantum efficiency (EQE) in light-emitting diodes (LEDs) based on isotropic quantum dots has approached the theoretical limit of close to 20%. Anisotropic nanorods can break this limit by taking advantage of their directional emission. However, the progress towards higher EQE by using CdSe/CdS nanorods (NRs) faces several challenges, primarily involving the low quantum yield and unbalanced charge injection in devices. Herein, the seeded growth method is modified and anisotropic nanorods are obtained with photoluminescence quantum yield up to 98% by coating a gradient alloyed CdZnSe shell around conventional spherical CdSe seeds. This intermediate alloyed CdZnSe shell combined with a subsequent rod-shaped CdZnS/ZnS shell can effectively suppress the electron delocalization in the typical CdSe/CdS nanorods due to their small conduction bandgap offset. Additionally, this alloyed shell can reduce the hole-injection barrier and create a larger barrier for electron injection, both effects promoting a balanced injection of electrons and holes in LEDs. Hence, LEDs are reached with high brightness (160341cd m-2) and high efficiency (EQE = 22%, current efficiency = 23.19cd A-1), which are the highest values to date for nanorod LEDs.

Exceptional Thermoelectric Performance of Cu2(Zn,Fe,Cd)SnS4 Thin Films.

High-quality Cu2(Zn,Fe,Cd)SnS4 (CZFCTS) thin films based on the parent CZTS were prepared by aerosol-assisted chemical vapor deposition (AACVD). Substitution of Zn by Fe and Cd significantly improved the electrical transport properties, and monophasic CZFCTS thin films exhibited a maximum power factor (PF) of ∼0.22 μW cm-1 K-2 at 575 K. The quality and performance of the CZFCTS thin films were further improved by postdeposition annealing. CZFCTS thin films annealed for 24 h showed a significantly enhanced maximum PF of ∼2.4 μW cm-1 K-2 at 575 K. This is higher than all reported values for single-phase quaternary sulfide (Cu2BSnS4, B = Mn, Fe, Co, Ni) thin films and even exceeds the PF for most polycrystalline bulk materials of these sulfides. Density functional theory (DFT) calculations were performed to understand the impact of Cd and Fe substitution on the electronic properties of CZTS. It was predicted that CZFCTS would have a smaller band gap than CZTS and a higher density of states (DoS) near the Fermi level. The thermal conductivity and thermoelectric figure of merit (zT) of the CZFCTS thin films have been evaluated, yielding an estimated maximum zT range of 0.18-0.69 at 550 K. The simple processing route and improved thermoelectric performance make CZFCTS thin films extremely promising for thermoelectric energy generation.

Induced out-of-plane piezoelectricity and giant Rashba spin splitting in Janus WSiZ3H (Z = N, P, As) monolayers toward next-generation electronic devices

Two-dimensional (2D) piezoelectric nanomaterials have widely been studied recently due to their promise for various applications in technology. Investigation of vertical piezoelectricity will contribute to a deeper understanding of the intrinsic mechanism of piezoelectric effects in the 2D structures. In this paper, we report a first-principle study for the structural, electronic, piezoelectric, and transport properties of new-designed Janus WSiZ3H (Z= N, P, and As) monolayers. The structural stability of WSiZ3H is theoretically confirmed based on the energetic, phonon dispersion, and also elastic analyses. At the ground state, while WSiN3H is an indirect semiconductor, both WSiP3H and WSiAs3H are predicted to be direct semiconductors with smaller bandgaps. When the spin-orbit coupling effects are taken into account, a large valley spin splitting is observed at the K point of WSiZ3H materials. Interestingly, a giant Rashba spin splitting is found in WSiP3H and WSiAs3H with Rashba constant αR up to 770.91 meV Å. Additionally, our first-principles study indicates that Janus WSiZ3H monolayers are piezoelectric semiconductors with high out-of-plane piezoelectric coefficient |d31|, up to 0.15 pm/V, due to the broken mirror symmetry. Besides, with high electron mobilities and also possessing direct band gaps, WSiP3H and WSiAs3H monolayers are favorable for applications in optoelectronics.

Accurate and rapid predictions with explainable graph neural networks for small high-fidelity bandgap datasets

Accurate and rapid bandgap prediction is a fundamental task in materials science. We propose graph neural networks with transfer learning to overcome the scarcity of training data for high-fidelity bandgap predictions. We also add a perturbation-based component to our framework to improve explainability. The experimental results show that a framework consisting of graph-level pre-training and standard fine-tuning achieves superior performance on all high-fidelity bandgap prediction tasks and training-set sizes. Furthermore, the framework provides a reliable explanation that considers node features together with the graph structure. We also used the framework to screen 105 potential photovoltaic absorber materials.

Strain-Induced Topological Phase Transitions Covering the Indicator in Orthorhombic Li2AuBi.

The symmetry indicator is widely used to classify topological materials hosting inversion symmetry. We find orthorhombic Li2AuBi in space group Cmcm is a topological insulator with under no strain via first-principles calculations. Due to small band gaps in the kz = 0 plane, the band inversions can be selectively induced by moderate external strains to realize phases covering all values of = 1, 2, 3, and 0. Detailed phase diagrams are plotted under various moderate strains. The (001) surface states and their associated Fermi surfaces and spin textures are calculated. The topological surface states have different connectivities and different spin textures for the four different phases. The tunability of topological surface states via moderate strain suggests Li2AuBi as an attractive topological material for device applications.

Geometry optimization and energy parameter calculations using density-functional theory method and molecular docking of anticonvulsant therapeutic metal complexes of gabapentin

This work aims to give computational studies of Mn(II), Co(II), Ni(II) and Cu(II) complexes of gabapentin (Gpn), formulized as [M(Gpn)(H2O)3(Cl)].nH2O complexes (where n = 2-6), using DFT method. They were previously synthesized and characterized. DFT calculations are in good agreement with practical studies. Bond lengths of metal complexes reduced or increased rather than that of ligand due to complexation. Bond angles of complexes predict the octahedral environment around the central metal ions predicting sp3d2 or d2sp3hybridization. The calculated energy parameters are negative indicating stability of metal complexes. The small energy band gap of compounds predicts the higher biological activity and high tendency of electron transfer. The comparable frequencies of theoretical and experimental IR may be attributed to different phases of measurement. The induced fit docking SP G-score of the molecular interactions of drug (Gpn) and its metal(II) complexes show that all investigated compounds have a good interaction towards sertonine receptor 5-HT2C and D2 dopamine receptor proteins. Co(II)-Gpn interacts with active site residues of sertonine receptor 5-HT2C with an excellent dock score of -7.370 kcal/mol and RMSD = 1.581 Å. On the other hand, Ni(II)-Gpn has the best dock score of -6.638 kcal/mol and RMSD = 1.995 Å with D2 dopamine receptor.
 KEY WORDS: Gabapentin, Transition metals, DFT-method, molecular docking
 Bull. Chem. Soc. Ethiop. 2024, 38(2), 511-526. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i2.18

Interfacial-Confined Isochronous Conversion to Biphasic Selenide Heterostructure with Enhanced Adsorption Behaviors for Robust High-Rate Na-Ion Storage.

Sodium-ion batteries (SIBs) have gradually become one of the most promising energy storage techniques in the current era of post-lithium-ion batteries. For anodes, transitional metal selenides (TMSe) based materials are welcomed choices , owing to relatively higher specific capacities and enriched redox active sites. Nevertheless, current bottlenecks are blamed for their poor intrinsic electronic conductivities, and uncontrollable volume expansion during redox reactions. Given that, an interfacial-confined isochronous conversion strategy is proposed, to prepare orthorhombic/cubic biphasic TMSe heterostructure, namely CuSe/Cu3 VSe4 , through using MXene as the precursor, followed by Cu/Se dual anchorage. As-designed biphasic TMSe heterostructure endows unique hierarchical structure, which contains adequate insertion sites and diffusion spacing for Na ions, besides, the surficial pseudocapacitive storage behaviors can be also proceeded like 2D MXene. By further investigation on electronic structure, the theoretical calculations indicate that biphasic CuSe/Cu3 VSe4 anode exhibits well-enhanced properties, with smaller bandgap and thus greatly improves intrinsic poor conductivities. In addition, the dual redox centers can enhance the electrochemical Na ions storage abilities. As a result, the as-designed biphasic TMSe anode can deliver a reversible specific capacity of 576.8mAhg-1 at 0.1Ag-1 , favorable Na affinity, and reduced diffusion barriers. This work discloses a synchronous solution toward demerits in conductivities and lifespan, which is inspiring for TMSe-based anode development in SIBs systems.

Determining the Structural Properties and Vibrational Modes of Annealed Lead Composite Material Deposit

Techniques for effectively harnessing lead (Pb) deposits for optimum utilization have attracted a lot of research interest. Results obtained from investigating the elemental composition, vibrational modes, and structural properties of a fired Pb composite deposit, which is purified using an electric kiln furnace and further annealed in palladium‐diffused hydrogen ambient, are reported in the present study. Both atomic force microscopy and scanning electron microscopy analysis on the deposit indicate that the Pb composite is composed of crystal‐like morphology. The vibrational modes obtained from the material are identical to the Raman spectrum reported for PbSO4. Also, data acquired from the energy‐dispersive X‐ray analysis of the annealed Pb composite material confirm the presence of zinc, carbon, silicon, sulfur, and oxygen in the material. At the same time, Pb appears to be the primary constituent with reference to its weight percentage composition compared to other elements. The findings from the present study may be vital for providing an improved understanding of the electronic and structural properties of the annealed Pb composite deposit while promoting the development of a feasible approach for the recovery and recycling of Pb for future related applications.

Performance potential of transistors based on tellurium nanowire arrays: A quantum transport study

Low-dimensional nanomaterials provide promising material platforms for aggressively scaled transistor technologies. We assess the performance potential of transistors based on an array of Tellurium nanowires (TNWs), by parameterizing a machine-learning (ML) tight-binding model with quantum transport device simulations. It has been shown that a transistor based on a parallel array of carbon nanotubes (CNTs) can have excellent on-state performance, but the small bandgap limits the transistor scalability and off-state performance. Our results indicate that compared to the CNT array FETs, the TNW array FETs have significantly suppressed ambipolar transport and improved subthreshold characteristics. The TNW array FET has the potential to achieve a near-ideal subthreshold swing (SS) close to 60 mV/dec, a very large on–off ratio (>109), and low source-drain leakage current at a 10 nm-scale channel length, due to its excellent gate electrostatics with a gate-all-around (GAA) structure, larger band gap and reduced quantum–mechanical tunneling. The TNW array FET also shows excellent scalability with a SS below 100 mV/dec when the channel length is further scaled down to 5 nm. Its larger bandgap and heavier effective mass significantly reduce quantum tunneling. This mechanism contributes to improved subthreshold and lower leakage but also highlights the need to develop low Schottky barrier contacts for TNWs.

Tuning of end-groups in diketopyrrolopyrrole-based acceptors molecules for organic photovoltaics

In this computational approach, four small novel acceptor molecules of A2-D-A1-D-A2 type have been designed (S1-S4) by the replacement of terminal acceptor groups (A2) of R molecule with four different types of electron accepting-units. The photovoltaic aspects of molecules have been studied by using DFT based method i.e. B3LYP/6–31 G (d, p). The energy level of ground and excited state, bandgap (Egap), excitation energy, transition density matrix (TDM), absorption maxima (λmax), light-harvesting efficiency (LHE), the density of states (DOS), open circuit voltage (VOC) and many other optoelectronic properties of molecules have been investigated in this research. Out of all the newly suggested molecules, S2 has exhibited the highest red-shift in λmax (815 nm), the lowest excitation energy (1.52 eV), small band gap and ionization potential, and the highest oscillator strength (1.97). The VOC of the studied acceptor molecules was calculated with regard to the PTB7-Th donor, and the findings showed that all of the newly suggested molecules displayed a higher VOC and a greater FF than that of R molecule. Consequently, the findings of these calculations show that our computational investigations give profound insights to support a realistic implementation of OSCs with the accepted acceptor molecules examined.

Dielectric, electrical and optical properties of a Ni-substituted double perovskite ceramic

In this report, iron based double perovskite oxide Ca2Fe0.85Ni0.15NbO6 was successfully synthesized adopting the solid state reaction method. The structure and microstructure along with the purity, frequency and temperature dependent dielectric properties, energy storage and band gap modulation properties of the ceramic is also discussed. The ceramic shows a small band gap with a high remnant polarization which aligns it toward ferroelectric photovoltaic device applications. The temperature stable dielectric constant of the material up to a high temperature range is useful for MLCC applications. The energy storage density of the material is calculated from room temperature hysteresis loop. The frequency variation of ac conductivity refers Jonscher’s law. The temperature variation of frequency exponent term n indicates CBH (correlated barrier hopping), model of the conduction mechanism in the sample. The presence of room temperature M-H loop with negligible magnetization and coercive value indicates the soft ferromagnetic behavior of the ceramic.

A first-principles study on the promising thermoelectric properties of SnX (X = S, Se, Te) compounds.

SnSe has emerged as an outstanding thermoelectric material due to its exceptional performance. In this study, first-principles calculations are employed to investigate the thermoelectric properties of materials within the SnX family, where X can be either S, Se, or Te. Initially, we assessed the stability of SnX (X = S, Se, Te). We found that SnS exhibits better mechanical and thermal stability than SnSe and SnTe. We then conduct phonon and electronic transport analysis. Following the general rule that heavier atoms have lower thermal conductivity, SnTe demonstrates lower thermal conductivity due to its low group velocity compared with SnS and SnSe. Regarding electrical transport properties, the band gaps for SnS, SnSe, and SnTe are 0.56, 0.54, and 0.35 eV, respectively. Notably, the small band gap and higher degeneracy in its band valleys for SnTe make it more effective for achieving a high power factor. The maximum ZT values are determined to be 1.41, 1.41, and 1.87 for SnS, SnSe, and SnTe, respectively. Remarkably, ZTmax of SnTe exceeds that of SnSe by 32.6%. Overall, the results clearly demonstrate that SnTe exhibits superior thermoelectric properties compared to SnSe and SnS. This study provides valuable insights into the electronic structure, thermal conductivity, and mechanical and thermal stability of materials within the SnSe family, such as SnS or SnTe, without the need for extensive and costly experimental work.

π-extended pyrenes: from an antiaromatic buckybowl to doubly curved nanocarbons with gulf architectures.

The synthesis of π-extended pyrenes keeps attracting considerable attention. In particular, frameworks containing nonbenzenoid rings might display intriguing properties. Here, we report a practical synthetic pathway to access a new buckybowl (1), which is composed of four five-membered rings externally fused to a pyrene core. The buckybowl 1 exhibits antiaromaticity involving 22 π-electrons, a rapid bowl-to-bowl interconversion, and a small band gap. Furthermore, this buckybowl could be subjected to Scholl cyclodehydrogenation to prepare the doubly curved nanocarbons (2rac and 2meso), which exist as two diastereomers, as demonstrated by X-ray crystal structure determination. Variable temperature 1H NMR measurements reveal that 2meso can isomerize into 2rac under thermal conditions, with an activation free energy of 27.1 kcal mol-1. Both the enantiomers of 2rac can be separated by chiral HPLC and their chiroptical properties are thoroughly examined. In addition, the nanocarbon 2meso with two gulf architectures facilitates host-guest chemistry with a variety of guests, including PDI, TDI, C60 and C70.

Nonadiabatic molecular dynamics study on effect of Ge/Sn alloy on hot carrier relaxation of CsPbBr<sub>3</sub> perovskite

Perovskite solar cells have been a prominent focus in the field of photovoltaics in recent decades, owing to their exceptional performance: easy synthesis, and cost-effectiveness. The all-inorganic cesium-based perovskite CsPbBr<sub>3</sub>, known for its remarkable thermal stability, has become a star material in the field of optoelectronics due to its outstanding luminescent properties. Despite the high efficiency of lead-based perovskite solar cells, the toxicity associated with lead and the poor long-term stability of these devices remain significant barriers to their large-scale commercialization. As is well known, non-radiative electron-hole recombination significantly shortens the carrier lifetime, acting as a primary pathway for excited state charge to loss energy. This phenomenon directly affects the photovoltaic conversion efficiency and charge transfer performance of perovskite materials. Therefore, maximizing the reduction of non-radiative recombination energy loss in perovskite solar cells has become a crucial research focus. In this study, a systematic exploration is conducted by using a non-adiabatic molecular dynamics approach combined with time-dependent density functional theory to investigate the excited-state carrier dynamics of CsPbBr<sub>3</sub> and its alloyed structures, CsPb<sub>0.75</sub>Ge<sub>0.25</sub>Br<sub>3</sub> and CsPb<sub>0.5</sub>Ge<sub>0.25</sub>Sn<sub>0.25</sub>Br<sub>3</sub>. The study comprehensively analyzes the non-radiative electron-hole recombination scenarios and the mechanisms for reducing charge energy loss based on crystal structure, electronic properties, and excited-state properties. The research findings reveal that alloying with Sn/Ge can reduce the bandgap, increase non-adiabatic coupling, and shorten the decoherence time. The interplay of reduced quantum decoherence, smaller bandgap, and larger non-adiabatic coupling effectively decelerates the electron-hole recombination process. Consequently, the carrier lifetime of the CsPb<sub>0.75</sub>Ge<sub>0.25</sub>Br<sub>3</sub> system extends by 1.6 times. Moreover, under the joint influence of Sn/Ge, the carrier lifetime of the CsPb<sub>0.5</sub>Ge<sub>0.25</sub>Sn<sub>0.25</sub>Br<sub>3</sub> system extends by 4.2 times compared with those of the original system. The overall sequence follows CsPb<sub>0.5</sub>Ge<sub>0.25</sub>Sn<sub>0.25</sub>Br<sub>3</sub> > CsPb<sub>0.75</sub>Ge<sub>0.25</sub>Br<sub>3</sub> > CsPbBr<sub>3</sub>. This study underscores the significant influence of binary alloying of B-site metal cations (in the perovskite structure <i>ABX</i><sub>3</sub>, where B-site refers to the metal cation) on the non-radiative electron-hole recombination of CsPbBr<sub>3</sub>.This research presents an effective alloying scheme that substantially prolongs the carrier lifetime of perovskites, offering a rational approach to optimizing solar cell performance. It lays the groundwork for the future design of perovskite solar cell materials.

Investigating the influence of Cu and Ti substitution on the structural, optical, and dielectric properties of BiFeO3.

The environmentally friendly BiFe1-x(Ti1/2Cu1/2)xO3 system with various substitution rates, including x = 0 (BFO), x = 0.02 (BFTCO2) and x = 0.04 (BFTCO4), has been synthesized using the solid-state reaction technique. All compositions exhibited a distorted rhombohedral structure with R3c space, as observed from the results of XRD and Raman spectroscopy. A significant impurity phase (Bi25FeO40) appears in pure and doped BFO, with a percentage ranging between 6 and 9%. This impurity was also detected using Mössbauer spectroscopy. UV-vis spectroscopy revealed a decrease in optical band energy with the substitution, suggesting the potential applications of doped BFO within the visible range of the spectrum, making it suitable for photocatalytic and solar cell applications. The smallest bandgap was observed for BFTCO2 with Eg = 1.93 eV. The origin of this reduction is discussed from a scientific point of view. Furthermore, Cu2+ and Ti4+ co-doped BFO display an improvement in dielectric properties due to the reduction in the value of tan δ. Dielectric measurements revealed an anomaly below TN with diffusive and dispersive behavior, suggesting a relaxor-like behavior for all compositions. The relaxor character was quantified by using the Vogel-Fulcher relationship which yielded activation energy of 0.359-0.614 eV. In our system, the relaxor behavior showed an enhancement with the heterogeneity created by the substitution rate, reaching its maximum for BFTCO4, characterized by the empirical parameters which are: ΔTrelax = 96 K and γ = 1.96. Finally, co-doped BFO ceramics not only present promising materials for optical applications due to the narrow bandgap, but their relaxor behavior can also be tailored for promising applications in high-energy storage devices.

Novel synthesis of Cl/N Co-doped TiO2 nanoparticles for enhanced photocatalytic activity

The N/Cl co-doped TiO2 nanostructures were studied as photocatalyst for rhodamine B (RhB), Methylene Blue (MB), and Methyl Orange (MO) degradation. A Commercial TiO2 (P25) grade was also compared to our materials. The N/Cl co-doped TiO2 at different Ti4+ precursors were synthesized by the co-precipitation method. The structural, surface morphology, and surface area were analyzed by XRD, SEM, TEM, and BET. Optical properties of samples were investigated by UV-visible spectroscopy showing that the N/Cl co-doped TiO2 has smaller bandgap than the P25. Overall, the improved N/Cl co-doped TiO2 samples showed better performance than the P25 for RhB, MB and MO degradations.

A giant intrinsic photovoltaic effect in atomically thin ReS2.

The photovoltaic (PV) effect in non-centrosymmetric materials consisting of a single component under homogeneous illumination can exceed the fundamental Shockley-Queisser limit compared to the traditional p-n junctions. Two-dimensional (2D) materials with a reduced dimensionality and smaller bandgap were predicated to be better candidates for the PV effect with high efficiency exceeding that of traditional ferroelectric perovskite oxides. Here, we report the giant intrinsic PV effect in atomically thin rhenium disulfide (ReS2) with centrosymmetry breaking. In graphene/ReS2/graphene sandwich structures, significant short-circuit currents (Isc) were observed with illumination over the visible spectral range, presenting the highest responsivity (110 mA W-1) and external quantum efficiency (25.7%) among those reported PV effects in 2D materials. This giant PV effect could be ascribed to the spontaneous-polarization induced depolarization field in even-number-layered ReS2 flakes benefiting from the distorted 1T lattice structure. Our results provide a new potential candidate material for the development of novel high-efficiency, miniaturized and easily integrated photodetectors and solar cells.

Modeling and tuning the electronic, mechanical and optical properties of a recently synthesized 2D polyaramid: a first principles study.

This work delves into a methodology of modeling 2D materials and their structural engineering, considering an example of a recently synthesized 2D polyaramid (2DPA-1). A bottom-up approach similar to experimental techniques is implemented for modeling, and then its electronic structures and phonon spectrum and the quadratic nature of flexural phonons are analyzed. Furthermore, boron and nitrogen atoms are substituted for the carbon atom of the amide group of 2DPA-1, and their effects on its electronic properties, phonon spectrum, and mechanical properties are compared with those of pristine 2DPA-1 using density functional theory calculations. The ab initio molecular dynamics (AIMD) simulations validate the thermal stability of our system at high temperatures. The spin-polarized electronic structures reveal the transformation of pristine 2DPA-1 from a semiconductor to a half-metal and its magnetic behaviour upon nitrogen substitution. Constraining the quadratic nature of flexural phonons using the Born-Huang criteria significantly enhances the phonon spectra, leading to more accurate and reliable simulations. For modulated 2DPA-1, the elastic modulus varies between 17 and 27 N m-1, and the absorption peaks shift from ∼5.15 eV to 2.42 eV, enabling the application of polymeric 2D nanomaterials in photocatalysis and sensing, where light absorption in the near-infrared region is important. Finally, validation of our methodology is confirmed, as computed Young's modulus (11.26-11.76 GPa) of 2DPA-1 matches excellently with the experimental value (12.7 ± 3.8 GPa). Overall, this study reveals the modeling of a newly synthesized polymeric 2D material, and tuning its properties results in smaller bandgaps and half-metallic and magnetic behaviours.

Second-harmonic generation in 2D moiré superlattices composed of bilayer transition metal dichalcogenides.

Moiré superlattices (MSLs) in twisted two-dimensional van der Waals materials feature twist-angle-dependent crystal symmetry and strong optical nonlinearities. By adjusting the twist angle in bilayer van der Waals materials, the second-harmonic generation (SHG) can be controlled. Here, we focus on exploring the electronic and SHG properties of MSLs in 2D bilayer transition metal dichalcogenides (TMDs) with different twist angles through first-principles calculations. We constructed MSL structures of five TMD materials, including three single-phase materials (MoS2, WS2, and MoSe2) and two heterojunctions (MoS2/MoSe2 and MoS2/WS2) with twist angles of 9.4°, 13.2°, 21.8°, 32.2°, and 42.1° without lattice mismatch. Our findings demonstrate a consistent variation in the SHG susceptibility among different TMD MSLs as a response to twist-angle changes. The underlying reason for the twist-angle dependence of SHG is that the twist angle regulates the interlayer coupling strength, affecting the optical band gap of MSLs and subsequently tuning the SHG susceptibility. Through a comparison of the static SHG susceptibility values, we identified the twist angle of 9.4° as the configuration that yields the highest SHG susceptibility (e.g. 358.5 pm V-1 for the 9.4° MoSe2 MSL). This value is even twice that of the monolayer (173.3 pm V-1 for monolayer MoSe2) and AA'-stacked bilayer structures (139.8 pm V-1 for AA' MoSe2). This high SHG susceptibility is attributed to the strong interlayer coupling in the 9.4° MSL, which enhances the valence band energy (contributed by the antibonding orbitals of chalcogen-pz and transition metal-dz2) and consequently leads to a small optical band gap, thus improving the optical transitions. The findings of this study provide a straightforward way to improve the SHG performance of bilayer TMDs and also throw light on the sensitive relationship between the twist angle, band structure and SHG properties of TMD MSLs.