All-inorganic lead-free perovskite solar cells have emerged as environmentally benign candidates;however,their device performance is still constrained by pronounced carrier recombination losses in the bulk and at inte...All-inorganic lead-free perovskite solar cells have emerged as environmentally benign candidates;however,their device performance is still constrained by pronounced carrier recombination losses in the bulk and at interfaces.By combining energy band alignment analysis with detailed modeling of recombination mechanisms,a systematic strategy for optimizing hole transport layers is developed.The results reveal that a negative valence band offset produces a cliff-like interface,which facilitates hole extraction while also accounting for the observed variations in open-circuit voltage.Furthermore,short-circuit current losses are quantitatively attributed to different recombination pathways,modeled by incorporating radiative,Shockley–Read–Hall,Auger,and interface recombination processes.This comprehensive approach not only clarifies the correlation between energy level alignment and recombination dynamics but also highlights the competing roles of band offset and interface defects in determining device performance.The optimized device architecture,based on Ge-based lead-free perovskites,achieves a power conversion efficiency of 25.1%,with an open-circuit voltage of 1.29 V,a short-circuit current density of 22.5 mA·cm^(-2),and a fill factor of 86.3%.These findings provide theoretical guidance for designing stable,high-performance,and environmentally friendly lead-free perovskite solar cells.展开更多
We have systematically studied the thermoelectric properties in Zn-doped Sn Te.Strikingly,band convergence and embedded precipitates arising from Zn doping,can trigger a prominent improvement of thermoelectric perform...We have systematically studied the thermoelectric properties in Zn-doped Sn Te.Strikingly,band convergence and embedded precipitates arising from Zn doping,can trigger a prominent improvement of thermoelectric performance.In particular,the value of dimensionless figure of merit z T has increased by 100% and up to ～ 0.5 at 775 K for the optimal sample with 2% Zn content.Present findings demonstrate that carrier concentration and effective mass play crucial roles on the Seebeck coefficient and power factor.The obvious deviation from the Pisarenko line（Seebeck coefficient versus carrier concentration） due to Zn-doping reveals the convergence of valence bands.When the doping concentration exceeds the solubility,precipitates occur and lead to a reduction of lattice thermal conductivity.In addition,bipolar conduction is suppressed,indicating an enlargement of band gap.The Zn-doped Sn Te is shown to be a promising candidate for thermoelectric applications.展开更多
Hydrogen peroxide(H_(2)O_(2))is one of the 100 most important chemicals in the world with high energy density and environmental friendliness.Compared with anthraquinone oxidation,direct synthesis of H_(2)O_(2) with hy...Hydrogen peroxide(H_(2)O_(2))is one of the 100 most important chemicals in the world with high energy density and environmental friendliness.Compared with anthraquinone oxidation,direct synthesis of H_(2)O_(2) with hydrogen(H_(2))and oxygen(O_(2)),and electrochemical methods,photocatalysis has the characteristics of low energy consumption,easy operation and less pollution,and broad application prospects in H_(2)O_(2) generation.Various photocatalysts,such as titanium dioxide(TiO_(2)),graphitic carbon nitride(g-C_(3)N_(4)),metal-organic materials,and nonmetallic materials,have been studied for H_(2)O_(2) production.Among them,g-C_(3)N_(4) materials,which are simple to synthesize and functionalize,have attracted wide attention.The electronic band structure of g-C_(3)N_(4) shows a bandgap of 2.77 eV,a valence band maximum of 1.44 V,and a conduction band minimum of−1.33 V,which theoretically meets the requirements for hydrogen peroxide production.In comparison to semiconductor materials like TiO_(2)(3.2 eV),this material has a smaller bandgap,which results in a more efficient response to visible light.However,the photocatalytic activity of g-C_(3)N_(4) and the yield of H_(2)O_(2) were severely inhibited by the electron-hole pair with high recombination rate,low utilization rate of visible light,and poor selectivity of products.Although previous reviews also presented various strategies to improve photocatalytic H_(2)O_(2) production,they did not systematically elaborate the inherent relationship between the control strategies and their energy band structure.From this point of view,this article focuses on energy band engineering and reviews the latest research progress of g-C_(3)N_(4) photocatalytic H_(2)O_(2) production.On this basis,a strategy to improve the H_(2)O_(2) production by g-C_(3)N_(4) photocatalysis is proposed through morphology control,crystallinity and defect,and doping,combined with other materials and other strategies.Finally,the challenges and prospects of industrialization of g-C_(3)N_(4) photocatalytic H_(2)O_(2) production are discussed and envisioned.展开更多
Hybrid transition-metal dichalcogenides （TMDs） with different chalcogens on each side （X-TM-Y） have attracted attention because of their unique properties. Nanotubes based on hybrid TMD materials have advantages i...Hybrid transition-metal dichalcogenides （TMDs） with different chalcogens on each side （X-TM-Y） have attracted attention because of their unique properties. Nanotubes based on hybrid TMD materials have advantages in flexibility over conventional TMD nanotubes. Here we predict the wide band gap tunability of hybrid TMD double-wall nanotubes （DWNTs） from metal to semiconductor. Using density-function theory （DFT） with HSE06 hybrid functional, we find that the electronic property of X-Mo-Y DWNTs （X = O and S, inside a tube; Y = S and Se, outside a tube） depends both on electronegativity difference and diameter difference. If there is no difference in electron negativity between inner atoms （X） of outer tube and outer atoms （Y） of inner tube, the band gap of DWNTs is the same as that of the inner one. If there is a significant electronegativity difference, the electronic property of the DWNTs ranges from metallic to semiconducting, depending on the diameter differences. Our results provide alternative ways for the band gap engineering of TMD nanotubes.展开更多
Two-dimensional monolayer copper selenide(CuSe)has been epitaxially grown and predicted to host the Dirac nodal line fermion(DNLF).However,the metallic state of monolayer CuSe inhibits the potential application of nan...Two-dimensional monolayer copper selenide(CuSe)has been epitaxially grown and predicted to host the Dirac nodal line fermion(DNLF).However,the metallic state of monolayer CuSe inhibits the potential application of nanoelectronic devices in which a band gap is needed to realize on/off properties.Here,we engineer the band structure of monolayer CuSe which is an analogue of a p-doped system via external atomic modification in an effort to realize the semiconducting state.We find that the H and Li modified monolayer CuSe shifts the energy band and opens an energy gap around the Fermi level.Interestingly,both the atomic and electronic structures of monolayer CuHSe and CuLiSe are very different.The H atoms bind on top of Se atoms of monolayer CuSe with Se-H polar covalent bonds,annihilating the DNLF band of monolayer CuSe dominated by Se orbitals.In contrast,Li atoms prefer to adsorb at the hexagonal center of CuSe,preserving the DNLF band of monolayer CuSe dominated by Se orbitals,but opening band gaps due to a slight buckling of the CuSe layer.The realization of metal-to-semiconductor transition from monolayer CuSe to CuXSe(X=H,Li)as revealed by first-principles calculations makes it possible to use CuSe in future electronic devices.展开更多
CuGaTe_(2)is p-type thermoelectric material with high thermoelectric potential.However,its performance is hindered by its intrinsic high resistivity and thermal conductivity.In this study,a synergistic strategy combin...CuGaTe_(2)is p-type thermoelectric material with high thermoelectric potential.However,its performance is hindered by its intrinsic high resistivity and thermal conductivity.In this study,a synergistic strategy combining band engineering and chemical bonding modulation is employed to simultaneously optimize the electrical and thermal transport properties of CuGaTe_(2).First-principles calculations reveal that Cd preferentially occupy Ga sites,leading to bandgap narrowing and increasing density of states near Fermi level.Consequently,both carrier concentration and density-of-states effective mass are simultaneously optimized,ultimately power factor reaches 1359μW·m^(-1)·K^(-2).Phonon dispersion analysis reveals that Cd doping induces acoustic-optical phonon avoided crossing behavior,decelerating phonon velocity.Combined with the increase of Grüneisen parameter and weakened chemical bonding,which significantly enhances lattice anharmonicity,leading to effectively reduce in lattice thermal conductivity.Microstructural characterization further reveals that CdTe doping leads to the formation of three-dimensional defect network consisting of point defects,dislocations,and stacking faults enhances phonon scattering.Ultimately,lattice thermal conductivity of doped sample is reduced to 0.81 W·m^(-1)·K^(-1).Consequently,(CuGaTe_(2))_(0.9975)(2CdTe)_(0.0025)sample achieves enhanced zT of 1.05 at 823 K.This work provides insights into the synergistic effects of band engineering and chemical bonding modulation,offering pathway for the design of thermoelectric materials.展开更多
The Zintl compound EuMg_(2)Sb_(2)is a promising thermoelectric material due to its inherently low lattice thermal conductivity and tunable electronic and thermal properties related to its multi-component nature.Howeve...The Zintl compound EuMg_(2)Sb_(2)is a promising thermoelectric material due to its inherently low lattice thermal conductivity and tunable electronic and thermal properties related to its multi-component nature.However,the large difference in electronegativity between Mg and Sb results in poor electronic transport properties,reducing its thermoelectric conversion efficiency and limiting its practical application.Thus,this study investigates a doping modification strategy for enhancing the thermoelectric performance of EuMg_(2)Sb_(2)and the microscopic mechanism using thefirst-principle calculations combined with the Boltzmann transport theory.Indeed,the larger energy separation at the valence band maximum is the key factor affecting the electronic transport properties of EuMg_(2)Sb_(2).The results demonstrate that Zn doping at the Mg site effectively increases the thermoelectric performance by promoting the valence band convergence owing to the close electronegativity to Sb and softening the phonon thus largely suppressing the lattice thermal conductivity.By optimizing the Zn doping concentration,the highestfigure of merit(zT)value is significantly increased to 2.24(2.66)in the x(z)direction at 800 K.The results suggest that the proposed modulation strategy and effect are of great significance for improving the thermoelectric performance of Zintl materials.展开更多
In recent years, transition metal phosphorus trichalcogenides MPX_(3)(M = transition metal, X = S, Se) have garnered significant attention in the field of two-dimensional van der Waals materials on account of their un...In recent years, transition metal phosphorus trichalcogenides MPX_(3)(M = transition metal, X = S, Se) have garnered significant attention in the field of two-dimensional van der Waals materials on account of their unique layered structures and diverse physical properties. In this work, we systematically investigated the vibrational modes and band gap evolution of ZnPSe_(3) under extreme conditions using Raman spectroscopy and high-pressure ultraviolet–visible(UV-vis) absorption spectroscopy. The experimental results demonstrate that the vibrational modes of ZnPSe_(3) remain stable at low temperatures(5–300 K) and high pressures(0–22.1 GPa). Notably, the band gap of ZnPSe_(3) exhibits an initial increase followed by a decrease under pressures ranging from 0 to 20.6 GPa, which is likely associated with a pressure-induced transition from an indirect to a direct band gap. This work not only enriches the understanding of van der Waals materials but also provides crucial experimental insights for their application in band gap engineering.展开更多
Constrained by severe bulk charge recombination,the actual photocurrent density of tantalum nitride(Ta_(3)N_(5))photoanode is much lower than the theoretical maximum value.Herein,we report the doping of phosphorus,a n...Constrained by severe bulk charge recombination,the actual photocurrent density of tantalum nitride(Ta_(3)N_(5))photoanode is much lower than the theoretical maximum value.Herein,we report the doping of phosphorus,a non-metallic element distinct from oxygen,into Ta_(3)N_(5),resulting in a photocurrent density 9 times higher than that of pristine Ta_(3)N_(5).Systematic characterization reveals that the phosphorus doping simultaneously enhances the bulk charge separation efficiency and surface charge injection efficiency of Ta_(3)N_(5),and induces favorable band energy restructuring.Specifically,a type-II homojunction formed between phosphorus-doped near-surface region and bulk Ta_(3)N_(5) effectively promotes the separation and transfer of photogenerated holes and electrons.Further modification with a Ni Fe-based cocatalyst enables the optimized photoanode to deliver a photocurrent density of 10 mA/cm^(2) at 1.23 V versus the reversible hydrogen electrode(RHE)and an applied bias photo-to-current efficiency of 1.78%at 0.95 V versus RHE.Our work provides a foundation for the development of a broader range of non-metal doped semiconductors.展开更多
The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of C...The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.展开更多
SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit.We synthesized polycrystalline Al_(x)Sn_(1-x)Se(x=0.01,0.02,0.03 and 0.04)by hot-pressing method,and...SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit.We synthesized polycrystalline Al_(x)Sn_(1-x)Se(x=0.01,0.02,0.03 and 0.04)by hot-pressing method,and combined theoretical estimation with experimental measurement to investigate the in-fluence of Al doping on thermoelectric properties of SnSe.It was found that dopant Al can effectively adjust the band structure of SnSe by introducing intermediate band.Al doping with low content(x=0.01 and 0.02)can introduce a single intermediate band close to the valence band maximum or conduction band minimum,achieving band engineering optimization.In high temperature region(498 K<T<823 K),the electronic transport properties significantly enhance with thermal excitation.The lattice thermal conductivity reduces with the Al atomic point defect scattering,leading to a low thermal conductivity of 0.47 W m^(-1) K^(-1) in Al_(0.04)Sn_(0.96)Se at 823 K.As a result,a high ZT of 0.84 at 823 K is obtained from the Al_(0.04)Sn_(0.96) Se perpendicular to the pressing direction,which is 58.5%larger than that of SnSe.In addition,dopant Al can adjust the anisotropy of polycrystalline SnSe.The anisotropy of electronic properties are enhanced with low doping level(x=0.01,0.02)and suppressed with high doping level(x=0.03,0.04).展开更多
Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is propo...Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is proposed for achieving electrical manipulation of a nonvolatile 180°magnetization reversal.A half semiconductor(HSC)and a bipolar magnetic semiconductor(BMS)are selected as the model of magnetic layers,whose conduction-band minimum and valence-band maximum are in the same and opposite spin states,respectively.Based on the analysis of virtual hopping and tight-binding models,the interlayer coupling of HSC/insulator/BMS devices is successfully tuned between ferromagnetic and antiferromagnetic interactions by varying electric field directions.Moreover,the interlayer coupling nearly disappears after removing the electric field,proving the nonvolatile magnetization reversal.Using first-principles calculations,the feasibility of present design strategy is further confirmed by a representative device with the structure of CrBr3/h-BN/2H-VSe_(2).This design guideline and physical phenomena may open an avenue to explore magnetoelectric coupling mechanisms and develop next-generation spintronic devices.展开更多
SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intr...SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermo-electric applications.In the current work,we show that alloying of Se and S in SrFBi_(S) 2 reduces the optical band gap with the second conduction band serving as an electron-transport medium,simultaneously increasing the electron concentration and effective mass.In addition,the raw material Bi_(2)Se_(3) is shown to act as liquid adjuvant during the annealing process,favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering.Highly ordered lamellar grains are stacked perpendicular to the pressure direction,leading to enhanced mobility along this direction.The synthetic effect results in a maximum power factor of 5.58 μm W cm^(-1) K^(-2) at 523 K for SrFBiSSe and a peak zT=0.34 at 773 K,enhancements of 180%compared with those of pristine SrFBiS_(2).展开更多
Doping with various impurities is an effective approach to improve the photoelectrochemical properties of TiO2. Here, we explore the effect of oxygen vacancy on geometric and elec- tronic properties of compensated （i...Doping with various impurities is an effective approach to improve the photoelectrochemical properties of TiO2. Here, we explore the effect of oxygen vacancy on geometric and elec- tronic properties of compensated （i.e. V-N and Cr-C） and non-compensated （i.e. V-C and Cr-N） codoped anatase TiO2 by performing extensive density functional theory calculations. Theoretical results show that oxygen vacancy prefers to the neighboring site of metal dopant （i.e. V or Cr atom）. After introduction of oxygen vacancy, the unoccupied impurity bands located within band gap of these codoped TiO2 will be filled with electrons, and the posi- tion of conduction band offset does not change obviously, which result in the reduction of photoinduced carrier recombination and the good performance for hydrogen production via water splitting. Moreover, we find that oxygen vacancy is easily introduced in V-N codoped TiO2 under O-poor condition. These theoretical insights are helpful for designing codoped TiO2 with high photoelectrochemical performance.展开更多
Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthe...Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications.The engineering of their band structures holds great promise in the rational tuning of the electronic and optical properties of perovskite nanostructures,which is one of the keys to achieving efficient and multifunctional optoelectronic devices.In this article,we summarize recent advances in band structure engineering of perovskite nanostructures.A survey of bandgap engineering of nanostructured perovskites is firstly presented from the aspects of dimensionality tailoring,compositional substitution,phase segregation and transition,as well as strain and pressure stimuli.The strategies of electronic doping are then reviewed,including defect-induced self-doping,inorganic or organic molecules-based chemical doping,and modification by metal ions or nanostructures.Based on the bandgap engineering and electronic doping,discussions on engineering energy band alignments in perovskite nanostructures are provided for building high-performance perovskite p-n junctions and heterostructures.At last,we provide our perspectives in engineering band structures of perovskite nanostructures towards future low-energy optoelectronics technologies.展开更多
Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subje...Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.展开更多
Tuning of phosphor luminescence properties,including the emission energy/intensity and thermal stability,is an important way to develop superior luminescent materials for diverse applications.In this work,we discuss t...Tuning of phosphor luminescence properties,including the emission energy/intensity and thermal stability,is an important way to develop superior luminescent materials for diverse applications.In this work,we discuss the effect of band gap engineering and energy transfer on the luminescence properties of Ce^3+or Pr^3+doped(Y,Gd)AGG systems,and analyze the underlying reasons for their different phenomena.By using VUV-UV excitation spectra and constructing VRBE schemes,the changes of host band structure,5 d excited level energies and emission thermal stability of Ce^3+and Pr^3+with the incorporation of Gd^3+ions were studied.In addition,the energy transfer dynamics was also investigated in terms of the luminescence decay curves.This work demonstrates a way to tune phosphor luminescence properties by combining band gap engineering and energy transfer tailoring and provides an inspiring discussion on the different results of Ce^3+doping on the Ce^3+and Pr^3+emissions.展开更多
Atomically thin two-dimensional （2D） layered materials have potential applications in nanoelectronics, nanophoton- ics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for...Atomically thin two-dimensional （2D） layered materials have potential applications in nanoelectronics, nanophoton- ics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for their broad applications in high-performance integrated devices, such as broad-band photodetectors, multi-color light emitting diodes （LEDs）, and high-efficiency photovoltaic devices. In this review, we will summarize the recent progress on the controlled growth of composition modulated atomically thin 2D semiconductor alloys with band gaps tuned in a wide range, as well as their induced applications in broadly tunable optoelectronic components. The band gap engineered 2D semiconductors could open up an exciting opportunity for probing their fundamental physical properties in 2D systems and may find diverse applications in functional electronic/optoelectronic devices.展开更多
Artificially constructed van der Waals heterostructures(vdWHs)provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics.Two methods for building vdWHs have been developed:stacking ...Artificially constructed van der Waals heterostructures(vdWHs)provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics.Two methods for building vdWHs have been developed:stacking two-dimensional(2D)materials into a bilayer structure with different lattice constants,or with different orientations.The interlayer coupling stemming from commensurate or incommensurate superlattice pattern plays an important role in vdWHs for modulating the band structures and generating new electronic states.In this article,we review a series of novel quantum states discovered in two model vdWH systems—graphene/hexagonal boron nitride(hBN)hetero-bilayer and twisted bilayer graphene(tBLG),and discuss how the electronic structures are modified by such stacking and twisting.We also provide perspectives for future studies on hetero-bilayer materials,from which an expansion of 2D material phase library is expected.展开更多
As a low-bandgap ferroelectric material, BiFeO3 has gained wide attention for the potential photovoltaic applications,since its photovoltaic effect in visible light range was reported in 2009. In the present work, Bi...As a low-bandgap ferroelectric material, BiFeO3 has gained wide attention for the potential photovoltaic applications,since its photovoltaic effect in visible light range was reported in 2009. In the present work, Bi（Fe, Mn）O3thin films are fabricated by pulsed laser deposition method, and the effects of Mn doping on the microstructure, optical, leakage,ferroelectric and photovoltaic characteristics of Bi（Fe, Mn）O3 thin films are systematically investigated. The x-ray diffraction data indicate that Bi（Fe, Mn）O3 thin films each have a rhombohedrally distorted perovskite structure. From the light absorption results, it follows that the band gap of Bi（Fe, Mn）O3 thin films can be tuned by doping different amounts of Mn content. More importantly, photovoltaic measurement demonstrates that the short-circuit photocurrent density and the open-circuit voltage can both be remarkably improved through doping an appropriate amount of Mn content, leading to the fascinating fact that the maximum power output of ITO/BiFe（0.7）Mn（0.3）O3/Nb-STO capacitor is about 175 times higher than that of ITO/BiFeO3/Nb-STO capacitor. The improvement of photovoltaic response in Bi（Fe, Mn）O3 thin film can be reasonably explained as being due to absorbing more visible light through bandgap engineering and maintaining the ferroelectric property at the same time.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52102165 and 62474056)the Natural Science Foundation of Nanjing University of Posts and Telecommunications(Grant Nos.NY221029 and NY222165)。
文摘All-inorganic lead-free perovskite solar cells have emerged as environmentally benign candidates;however,their device performance is still constrained by pronounced carrier recombination losses in the bulk and at interfaces.By combining energy band alignment analysis with detailed modeling of recombination mechanisms,a systematic strategy for optimizing hole transport layers is developed.The results reveal that a negative valence band offset produces a cliff-like interface,which facilitates hole extraction while also accounting for the observed variations in open-circuit voltage.Furthermore,short-circuit current losses are quantitatively attributed to different recombination pathways,modeled by incorporating radiative,Shockley–Read–Hall,Auger,and interface recombination processes.This comprehensive approach not only clarifies the correlation between energy level alignment and recombination dynamics but also highlights the competing roles of band offset and interface defects in determining device performance.The optimized device architecture,based on Ge-based lead-free perovskites,achieves a power conversion efficiency of 25.1%,with an open-circuit voltage of 1.29 V,a short-circuit current density of 22.5 mA·cm^(-2),and a fill factor of 86.3%.These findings provide theoretical guidance for designing stable,high-performance,and environmentally friendly lead-free perovskite solar cells.
基金Project supported by the National Natural Science Foundation of China(Grant No.51771126)the Youth Foundation of Science&Technology Department of Sichuan Province,China(Grant No.2016JQ0051)+3 种基金the Sichuan University Talent Introduction Research Funding(Grand No.YJ201537)the Sichuan University Outstanding Young Scholars Research Funding(Grant No.2015SCU04A20)the World First-Class University Construction Fundingthe Fundamental and Frontier Research in Chongqing(Grant No.CSTC2015JCYJBX0026)
文摘We have systematically studied the thermoelectric properties in Zn-doped Sn Te.Strikingly,band convergence and embedded precipitates arising from Zn doping,can trigger a prominent improvement of thermoelectric performance.In particular,the value of dimensionless figure of merit z T has increased by 100% and up to ～ 0.5 at 775 K for the optimal sample with 2% Zn content.Present findings demonstrate that carrier concentration and effective mass play crucial roles on the Seebeck coefficient and power factor.The obvious deviation from the Pisarenko line（Seebeck coefficient versus carrier concentration） due to Zn-doping reveals the convergence of valence bands.When the doping concentration exceeds the solubility,precipitates occur and lead to a reduction of lattice thermal conductivity.In addition,bipolar conduction is suppressed,indicating an enlargement of band gap.The Zn-doped Sn Te is shown to be a promising candidate for thermoelectric applications.
基金This work was supported by the National Natural Science Foundation of China(42307566,22205084)China Postdoctoral Science Foundation(2023M742199,2023M741039)+1 种基金This project was fundedby the National&Local Joint Engineering Research Center for Mineral Salt Deep Utilization(SF202303)the State Key Laboratory of Efficient Utilization for LowGrade Phosphate Rock and Its Associated ResourcesWFKF(2023)013.
文摘Hydrogen peroxide(H_(2)O_(2))is one of the 100 most important chemicals in the world with high energy density and environmental friendliness.Compared with anthraquinone oxidation,direct synthesis of H_(2)O_(2) with hydrogen(H_(2))and oxygen(O_(2)),and electrochemical methods,photocatalysis has the characteristics of low energy consumption,easy operation and less pollution,and broad application prospects in H_(2)O_(2) generation.Various photocatalysts,such as titanium dioxide(TiO_(2)),graphitic carbon nitride(g-C_(3)N_(4)),metal-organic materials,and nonmetallic materials,have been studied for H_(2)O_(2) production.Among them,g-C_(3)N_(4) materials,which are simple to synthesize and functionalize,have attracted wide attention.The electronic band structure of g-C_(3)N_(4) shows a bandgap of 2.77 eV,a valence band maximum of 1.44 V,and a conduction band minimum of−1.33 V,which theoretically meets the requirements for hydrogen peroxide production.In comparison to semiconductor materials like TiO_(2)(3.2 eV),this material has a smaller bandgap,which results in a more efficient response to visible light.However,the photocatalytic activity of g-C_(3)N_(4) and the yield of H_(2)O_(2) were severely inhibited by the electron-hole pair with high recombination rate,low utilization rate of visible light,and poor selectivity of products.Although previous reviews also presented various strategies to improve photocatalytic H_(2)O_(2) production,they did not systematically elaborate the inherent relationship between the control strategies and their energy band structure.From this point of view,this article focuses on energy band engineering and reviews the latest research progress of g-C_(3)N_(4) photocatalytic H_(2)O_(2) production.On this basis,a strategy to improve the H_(2)O_(2) production by g-C_(3)N_(4) photocatalysis is proposed through morphology control,crystallinity and defect,and doping,combined with other materials and other strategies.Finally,the challenges and prospects of industrialization of g-C_(3)N_(4) photocatalytic H_(2)O_(2) production are discussed and envisioned.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0202300)the National Natural Science Foundation of China(Grant No.61390501)+3 种基金the National Basic Research Program of China(Grant No.2013CBA01600)Strategic Priority Research Program(B) of Chinese Academy of Sciences(Grant Nos.XDPB0601 and XDPB08-1)the CAS Pioneer Hundred Talents ProgramBeijing Nova Program,China(Grant No.Z181100006218023)
文摘Hybrid transition-metal dichalcogenides （TMDs） with different chalcogens on each side （X-TM-Y） have attracted attention because of their unique properties. Nanotubes based on hybrid TMD materials have advantages in flexibility over conventional TMD nanotubes. Here we predict the wide band gap tunability of hybrid TMD double-wall nanotubes （DWNTs） from metal to semiconductor. Using density-function theory （DFT） with HSE06 hybrid functional, we find that the electronic property of X-Mo-Y DWNTs （X = O and S, inside a tube; Y = S and Se, outside a tube） depends both on electronegativity difference and diameter difference. If there is no difference in electron negativity between inner atoms （X） of outer tube and outer atoms （Y） of inner tube, the band gap of DWNTs is the same as that of the inner one. If there is a significant electronegativity difference, the electronic property of the DWNTs ranges from metallic to semiconducting, depending on the diameter differences. Our results provide alternative ways for the band gap engineering of TMD nanotubes.
基金supported by the National Key Research&Development Projects of China(Grant No.2016YFA0202300)the National Natural Science Foundation of China(Grant No.61888102)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB30000000).
文摘Two-dimensional monolayer copper selenide(CuSe)has been epitaxially grown and predicted to host the Dirac nodal line fermion(DNLF).However,the metallic state of monolayer CuSe inhibits the potential application of nanoelectronic devices in which a band gap is needed to realize on/off properties.Here,we engineer the band structure of monolayer CuSe which is an analogue of a p-doped system via external atomic modification in an effort to realize the semiconducting state.We find that the H and Li modified monolayer CuSe shifts the energy band and opens an energy gap around the Fermi level.Interestingly,both the atomic and electronic structures of monolayer CuHSe and CuLiSe are very different.The H atoms bind on top of Se atoms of monolayer CuSe with Se-H polar covalent bonds,annihilating the DNLF band of monolayer CuSe dominated by Se orbitals.In contrast,Li atoms prefer to adsorb at the hexagonal center of CuSe,preserving the DNLF band of monolayer CuSe dominated by Se orbitals,but opening band gaps due to a slight buckling of the CuSe layer.The realization of metal-to-semiconductor transition from monolayer CuSe to CuXSe(X=H,Li)as revealed by first-principles calculations makes it possible to use CuSe in future electronic devices.
文摘CuGaTe_(2)is p-type thermoelectric material with high thermoelectric potential.However,its performance is hindered by its intrinsic high resistivity and thermal conductivity.In this study,a synergistic strategy combining band engineering and chemical bonding modulation is employed to simultaneously optimize the electrical and thermal transport properties of CuGaTe_(2).First-principles calculations reveal that Cd preferentially occupy Ga sites,leading to bandgap narrowing and increasing density of states near Fermi level.Consequently,both carrier concentration and density-of-states effective mass are simultaneously optimized,ultimately power factor reaches 1359μW·m^(-1)·K^(-2).Phonon dispersion analysis reveals that Cd doping induces acoustic-optical phonon avoided crossing behavior,decelerating phonon velocity.Combined with the increase of Grüneisen parameter and weakened chemical bonding,which significantly enhances lattice anharmonicity,leading to effectively reduce in lattice thermal conductivity.Microstructural characterization further reveals that CdTe doping leads to the formation of three-dimensional defect network consisting of point defects,dislocations,and stacking faults enhances phonon scattering.Ultimately,lattice thermal conductivity of doped sample is reduced to 0.81 W·m^(-1)·K^(-1).Consequently,(CuGaTe_(2))_(0.9975)(2CdTe)_(0.0025)sample achieves enhanced zT of 1.05 at 823 K.This work provides insights into the synergistic effects of band engineering and chemical bonding modulation,offering pathway for the design of thermoelectric materials.
基金the National Supercomputer Center in Tianjin,and the calculations were performed on TianHe-1(A).It was supported by grants from the General Program of National Natural Science Foundation of China(No.52372007)the General Q.Song,L.Bai,X.Gao et al.Journal of Materiomics 11(2025)1009107Program of Natural Science Foundation of Shandong Province(No.ZR2023ME125)+1 种基金the Taishan Industry Leading Talents Program(No.tscx202312007)Qilu Young Scholars Program of Shandong University.
文摘The Zintl compound EuMg_(2)Sb_(2)is a promising thermoelectric material due to its inherently low lattice thermal conductivity and tunable electronic and thermal properties related to its multi-component nature.However,the large difference in electronegativity between Mg and Sb results in poor electronic transport properties,reducing its thermoelectric conversion efficiency and limiting its practical application.Thus,this study investigates a doping modification strategy for enhancing the thermoelectric performance of EuMg_(2)Sb_(2)and the microscopic mechanism using thefirst-principle calculations combined with the Boltzmann transport theory.Indeed,the larger energy separation at the valence band maximum is the key factor affecting the electronic transport properties of EuMg_(2)Sb_(2).The results demonstrate that Zn doping at the Mg site effectively increases the thermoelectric performance by promoting the valence band convergence owing to the close electronegativity to Sb and softening the phonon thus largely suppressing the lattice thermal conductivity.By optimizing the Zn doping concentration,the highestfigure of merit(zT)value is significantly increased to 2.24(2.66)in the x(z)direction at 800 K.The results suggest that the proposed modulation strategy and effect are of great significance for improving the thermoelectric performance of Zintl materials.
基金Project supported by the National Key Research and Development Program of China (Grant Nos. 2021YFA1400204 and 2021YFA0718701)the National Natural Science Foundation of China (Grant Nos. 12204420, 12474021, and 12174347)。
文摘In recent years, transition metal phosphorus trichalcogenides MPX_(3)(M = transition metal, X = S, Se) have garnered significant attention in the field of two-dimensional van der Waals materials on account of their unique layered structures and diverse physical properties. In this work, we systematically investigated the vibrational modes and band gap evolution of ZnPSe_(3) under extreme conditions using Raman spectroscopy and high-pressure ultraviolet–visible(UV-vis) absorption spectroscopy. The experimental results demonstrate that the vibrational modes of ZnPSe_(3) remain stable at low temperatures(5–300 K) and high pressures(0–22.1 GPa). Notably, the band gap of ZnPSe_(3) exhibits an initial increase followed by a decrease under pressures ranging from 0 to 20.6 GPa, which is likely associated with a pressure-induced transition from an indirect to a direct band gap. This work not only enriches the understanding of van der Waals materials but also provides crucial experimental insights for their application in band gap engineering.
基金supported by the National Natural Science Foundation of China(Nos.22472071,21832005,22072168,22002175)the Natural Science Foundation of Gansu Province(No.21JR7RA440)Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA21061011)。
文摘Constrained by severe bulk charge recombination,the actual photocurrent density of tantalum nitride(Ta_(3)N_(5))photoanode is much lower than the theoretical maximum value.Herein,we report the doping of phosphorus,a non-metallic element distinct from oxygen,into Ta_(3)N_(5),resulting in a photocurrent density 9 times higher than that of pristine Ta_(3)N_(5).Systematic characterization reveals that the phosphorus doping simultaneously enhances the bulk charge separation efficiency and surface charge injection efficiency of Ta_(3)N_(5),and induces favorable band energy restructuring.Specifically,a type-II homojunction formed between phosphorus-doped near-surface region and bulk Ta_(3)N_(5) effectively promotes the separation and transfer of photogenerated holes and electrons.Further modification with a Ni Fe-based cocatalyst enables the optimized photoanode to deliver a photocurrent density of 10 mA/cm^(2) at 1.23 V versus the reversible hydrogen electrode(RHE)and an applied bias photo-to-current efficiency of 1.78%at 0.95 V versus RHE.Our work provides a foundation for the development of a broader range of non-metal doped semiconductors.
基金supported by the National Natural Science Foundation of China (Grant No. 51872006)the Excellent Youth Project of Natural Science Foundation of Anhui Province of China (Grant No. 2208085Y17)。
文摘The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.
基金For financial support,the authors are grateful to the funding support from the China Postdoctoral Science Foundation under grant number of 2019M653619the National Natural Science Foundation of China under grant numbers of 52006167,51825604 and 51721004the 111 Project under grant number of B16038.
文摘SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit.We synthesized polycrystalline Al_(x)Sn_(1-x)Se(x=0.01,0.02,0.03 and 0.04)by hot-pressing method,and combined theoretical estimation with experimental measurement to investigate the in-fluence of Al doping on thermoelectric properties of SnSe.It was found that dopant Al can effectively adjust the band structure of SnSe by introducing intermediate band.Al doping with low content(x=0.01 and 0.02)can introduce a single intermediate band close to the valence band maximum or conduction band minimum,achieving band engineering optimization.In high temperature region(498 K<T<823 K),the electronic transport properties significantly enhance with thermal excitation.The lattice thermal conductivity reduces with the Al atomic point defect scattering,leading to a low thermal conductivity of 0.47 W m^(-1) K^(-1) in Al_(0.04)Sn_(0.96)Se at 823 K.As a result,a high ZT of 0.84 at 823 K is obtained from the Al_(0.04)Sn_(0.96) Se perpendicular to the pressing direction,which is 58.5%larger than that of SnSe.In addition,dopant Al can adjust the anisotropy of polycrystalline SnSe.The anisotropy of electronic properties are enhanced with low doping level(x=0.01,0.02)and suppressed with high doping level(x=0.03,0.04).
基金supported by the National Natural Science Foundation of China(Grant No.52271238)the Liaoning Revitalization Talents Program(Grant No.XLYC2002075)+1 种基金the Research Funds for the Central University(Grant Nos.N2202004,and N2102012)funding from the Alexander von Humboldt Foundation(Grant No.CHN 1225715 HFST-P).
文摘Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is proposed for achieving electrical manipulation of a nonvolatile 180°magnetization reversal.A half semiconductor(HSC)and a bipolar magnetic semiconductor(BMS)are selected as the model of magnetic layers,whose conduction-band minimum and valence-band maximum are in the same and opposite spin states,respectively.Based on the analysis of virtual hopping and tight-binding models,the interlayer coupling of HSC/insulator/BMS devices is successfully tuned between ferromagnetic and antiferromagnetic interactions by varying electric field directions.Moreover,the interlayer coupling nearly disappears after removing the electric field,proving the nonvolatile magnetization reversal.Using first-principles calculations,the feasibility of present design strategy is further confirmed by a representative device with the structure of CrBr3/h-BN/2H-VSe_(2).This design guideline and physical phenomena may open an avenue to explore magnetoelectric coupling mechanisms and develop next-generation spintronic devices.
基金This work was financially supported by the National Key Research and Development Program of China(2018YFA0702100)the National Natural Science Foundation of China(21771123,52072234)J.Zhang is grateful for the support by the Open Project of Jiangsu Key Laboratory for Carbon-Based Functional Materials&Devices(KJS2023).
文摘SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermo-electric applications.In the current work,we show that alloying of Se and S in SrFBi_(S) 2 reduces the optical band gap with the second conduction band serving as an electron-transport medium,simultaneously increasing the electron concentration and effective mass.In addition,the raw material Bi_(2)Se_(3) is shown to act as liquid adjuvant during the annealing process,favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering.Highly ordered lamellar grains are stacked perpendicular to the pressure direction,leading to enhanced mobility along this direction.The synthetic effect results in a maximum power factor of 5.58 μm W cm^(-1) K^(-2) at 523 K for SrFBiSSe and a peak zT=0.34 at 773 K,enhancements of 180%compared with those of pristine SrFBiS_(2).
基金This work was supported by the National Natural Sci- ence Foundation of China （No.11034006, No.21273208, and No.21473168）, the Anhui Provincial Natural Sci- ence Foundation （No.1408085QB26）, the hmdamental Research Funds for the Central Universities, the China Postdoctoral Science Foundation （No.2012M511409）, and the Supercomputing Center of Chinese Academy of Sciences, Shanghai and USTC Supercomputer Cen- ters.
文摘Doping with various impurities is an effective approach to improve the photoelectrochemical properties of TiO2. Here, we explore the effect of oxygen vacancy on geometric and elec- tronic properties of compensated （i.e. V-N and Cr-C） and non-compensated （i.e. V-C and Cr-N） codoped anatase TiO2 by performing extensive density functional theory calculations. Theoretical results show that oxygen vacancy prefers to the neighboring site of metal dopant （i.e. V or Cr atom）. After introduction of oxygen vacancy, the unoccupied impurity bands located within band gap of these codoped TiO2 will be filled with electrons, and the posi- tion of conduction band offset does not change obviously, which result in the reduction of photoinduced carrier recombination and the good performance for hydrogen production via water splitting. Moreover, we find that oxygen vacancy is easily introduced in V-N codoped TiO2 under O-poor condition. These theoretical insights are helpful for designing codoped TiO2 with high photoelectrochemical performance.
基金support from Australian Research Council (ARC, FT150100450, IH150100006 and CE170100039)support from the MCATM and the FLEET+1 种基金the support from Shenzhen Nanshan District Pilotage Team Program (LHTD20170006)support from Guangzhou Science and Technology Program (Grant No. 201804010322)
文摘Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications.The engineering of their band structures holds great promise in the rational tuning of the electronic and optical properties of perovskite nanostructures,which is one of the keys to achieving efficient and multifunctional optoelectronic devices.In this article,we summarize recent advances in band structure engineering of perovskite nanostructures.A survey of bandgap engineering of nanostructured perovskites is firstly presented from the aspects of dimensionality tailoring,compositional substitution,phase segregation and transition,as well as strain and pressure stimuli.The strategies of electronic doping are then reviewed,including defect-induced self-doping,inorganic or organic molecules-based chemical doping,and modification by metal ions or nanostructures.Based on the bandgap engineering and electronic doping,discussions on engineering energy band alignments in perovskite nanostructures are provided for building high-performance perovskite p-n junctions and heterostructures.At last,we provide our perspectives in engineering band structures of perovskite nanostructures towards future low-energy optoelectronics technologies.
文摘Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.
基金Project supported by the National Natural Science Foundation of China(21671201,U1632101,61905289,11904425)Postdoctoral Science Foundation of China(2017M622846,2019M663202)。
文摘Tuning of phosphor luminescence properties,including the emission energy/intensity and thermal stability,is an important way to develop superior luminescent materials for diverse applications.In this work,we discuss the effect of band gap engineering and energy transfer on the luminescence properties of Ce^3+or Pr^3+doped(Y,Gd)AGG systems,and analyze the underlying reasons for their different phenomena.By using VUV-UV excitation spectra and constructing VRBE schemes,the changes of host band structure,5 d excited level energies and emission thermal stability of Ce^3+and Pr^3+with the incorporation of Gd^3+ions were studied.In addition,the energy transfer dynamics was also investigated in terms of the luminescence decay curves.This work demonstrates a way to tune phosphor luminescence properties by combining band gap engineering and energy transfer tailoring and provides an inspiring discussion on the different results of Ce^3+doping on the Ce^3+and Pr^3+emissions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11374092,61474040,61574054,and 61505051)the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province,Chinathe Science and Technology Department of Hunan Province,China(Grant No.2014FJ2001)
文摘Atomically thin two-dimensional （2D） layered materials have potential applications in nanoelectronics, nanophoton- ics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for their broad applications in high-performance integrated devices, such as broad-band photodetectors, multi-color light emitting diodes （LEDs）, and high-efficiency photovoltaic devices. In this review, we will summarize the recent progress on the controlled growth of composition modulated atomically thin 2D semiconductor alloys with band gaps tuned in a wide range, as well as their induced applications in broadly tunable optoelectronic components. The band gap engineered 2D semiconductors could open up an exciting opportunity for probing their fundamental physical properties in 2D systems and may find diverse applications in functional electronic/optoelectronic devices.
基金support from the National Natural Science Foundation of China(Grant No.11725418)the National Key Research and Development Program of China(Grant No.2016YFA0301004)+3 种基金Science Challenge Project,China(Grant No.TZ2016004)Beijing Advanced Innovation Center for Future Chip(ICFC)Tsinghua University Initiative Scientific Research Programfunded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)–TRR 173–268565370(projects A02)。
文摘Artificially constructed van der Waals heterostructures(vdWHs)provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics.Two methods for building vdWHs have been developed:stacking two-dimensional(2D)materials into a bilayer structure with different lattice constants,or with different orientations.The interlayer coupling stemming from commensurate or incommensurate superlattice pattern plays an important role in vdWHs for modulating the band structures and generating new electronic states.In this article,we review a series of novel quantum states discovered in two model vdWH systems—graphene/hexagonal boron nitride(hBN)hetero-bilayer and twisted bilayer graphene(tBLG),and discuss how the electronic structures are modified by such stacking and twisting.We also provide perspectives for future studies on hetero-bilayer materials,from which an expansion of 2D material phase library is expected.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274322,51402318,61404080,and 61675066)the National Key Technology Research and Development Program of China(Grant No.2016YFA0201102)the China Postdoctoral Science Foundation(Grant No.2016LH0050)
文摘As a low-bandgap ferroelectric material, BiFeO3 has gained wide attention for the potential photovoltaic applications,since its photovoltaic effect in visible light range was reported in 2009. In the present work, Bi（Fe, Mn）O3thin films are fabricated by pulsed laser deposition method, and the effects of Mn doping on the microstructure, optical, leakage,ferroelectric and photovoltaic characteristics of Bi（Fe, Mn）O3 thin films are systematically investigated. The x-ray diffraction data indicate that Bi（Fe, Mn）O3 thin films each have a rhombohedrally distorted perovskite structure. From the light absorption results, it follows that the band gap of Bi（Fe, Mn）O3 thin films can be tuned by doping different amounts of Mn content. More importantly, photovoltaic measurement demonstrates that the short-circuit photocurrent density and the open-circuit voltage can both be remarkably improved through doping an appropriate amount of Mn content, leading to the fascinating fact that the maximum power output of ITO/BiFe（0.7）Mn（0.3）O3/Nb-STO capacitor is about 175 times higher than that of ITO/BiFeO3/Nb-STO capacitor. The improvement of photovoltaic response in Bi（Fe, Mn）O3 thin film can be reasonably explained as being due to absorbing more visible light through bandgap engineering and maintaining the ferroelectric property at the same time.
