Quasi-2D Dion-Jacobson(DJ)tin halide perovskite has attracted much attention due to its elimination of Van der Waals gap and enhanced environmental stability.However,the bulky organic spacers usually form a natural qu...Quasi-2D Dion-Jacobson(DJ)tin halide perovskite has attracted much attention due to its elimination of Van der Waals gap and enhanced environmental stability.However,the bulky organic spacers usually form a natural quantum well structure,which brings a large quantum barrier and poor film quality,further limiting the carrier transport and device performance.Here,we designed three organic spacers with different chain lengths(ethylenediamine(EDA),1,3-propanediamine(PDA),and 1,4-butanediamine(BDA))to investigate the quantum barrier dependence.Theoretical and experimental characterizations indicate that EDA with short chain can reduce the lattice distortion and dielectric confinement effect,which is beneficial to the effective dissociation of excitons and the inhibition of trap-free non-radiative relaxation.In addition,EDA cation shows strong interaction with the inorganic octahedron,realizing large aggregates in precursor solution and high-quality films with improved structural stability.Furthermore,femtosecond transient absorption proves that EDA cations can also weaken the formation of small n-phases with large quantum barrier to achieve effective carrier transport between different nphases.Finally,the quasi-2D DJ(EDA)FA_(9)Sn_(10)I_(31)solar cells achieves a 7.07%power conversion efficiency with good environment stability.Therefore,this work sheds light on the regulation of the quantum barrier and carrier transport through the chain length of organic spacer for qua si-2D DJ lead-free perovskites.展开更多
Interface roughness strongly influences the performance of germanium metal-organic-semiconductor field effect transistors (MOSFETs). In this paper, a 2D full-band Monte Carlo simulator is used to study the impact of...Interface roughness strongly influences the performance of germanium metal-organic-semiconductor field effect transistors (MOSFETs). In this paper, a 2D full-band Monte Carlo simulator is used to study the impact of interface roughness scattering on electron and hole transport properties in long- and short- channel Ge MOSFETs inversion layers. The carrier effective mobility in the channel of Ge MOSFETs and the in non-equilibriurn transport properties are investigated. Results show that both electron and hole mobility are strongly influenced by interface roughness scattering. The output curves for 50 nm channel-length double gate n and p Ge MOSFET show that the drive currents of n- and p-Ge MOSFETs have significant improvement compared with that of Si n- and p-MOSFETs with smooth interface between channel and gate dielectric. The 82% and 96% drive current enhancement are obtained for the n- and p-MOSFETs with the completely smooth interface. However, the enhancement decreases sharply with the increase of interface roughness. With the very rough interface, the drive currents of Ge MOSFETs are even less than that of Si MOSFETs. Moreover, the significant velocity overshoot also has been found in Ge MOSFETs.展开更多
All-inorganic Cs_(3)Bi_(2)I_(9)(CBI)halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability.Unfortunately,the discrete molecular[Bi2I9]3−clu...All-inorganic Cs_(3)Bi_(2)I_(9)(CBI)halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability.Unfortunately,the discrete molecular[Bi2I9]3−clusters limit the charge-transport behaviors.Herein,the defect halide perovskite based on trivalent Bi^(3+)is expanded to Cs_(3)Bi_(2)I_(6)Br_(3)(CBIB).Centimeter-size CBIB single crystal(Φ15×70 mm^(3))was grown by the vertical Bridgeman method.The powder X-ray diffraction analysis shows that CBIB has structure with lattice parameters of a=b=8.223Å,c=10.024Å,α=β=90°andγ=120°.The density functional theory(DFT)calculations demonstrate that the charge density distribution was enhanced after the dimensional expansion.The enhancement of carrier transport ability of(00l)in-plane is characterized before and after dimensional improvement.The obtained CBIB(001)exhibited an electron mobility up to 40.03 cm^(2)V^(−1)s^(−1)by time-of-flight(TOF)technique,higher than 26.46 cm^(2)V^(−1)s^(−1)of CBI(001).Furthermore,the X-ray sensitivity increases from 707.81μC Gy^(−1)cm^(−2)for CBI(001)to 3194.59μC Gy−1 cm^(−2)for CBIB(001).This research will deepen our understanding of Bi-based perovskite materials and afford more promising strategies for lead-free perovskite optoelectronic devices modification.展开更多
The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and witho...The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.展开更多
We established a model for investigating polycrystalline silicon(poly-Si) thin film transistors(TFTs).The effect of grain boundaries(GBs) on the transfer characteristics of TFT was analyzed by considering the nu...We established a model for investigating polycrystalline silicon(poly-Si) thin film transistors(TFTs).The effect of grain boundaries(GBs) on the transfer characteristics of TFT was analyzed by considering the number and the width of grain boundaries in the channel region,and the dominant transport mechanism of carrier across grain boundaries was subsequently determined.It is shown that the thermionic emission(TE) is dominant in the subthreshold operating region of TFT regardless of the number and the width of grain boundary.To a poly-Si TFT model with a 1 nm-width grain boundary,in the linear region,thermionic emission is similar to that of tunneling(TU),however,with increasing grain boundary width and number,tunneling becomes dominant.展开更多
Carrier transport via the V-shaped pits (V-pits) in InGaN/GaN multiple-quantum-well (MQW) solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths fo...Carrier transport via the V-shaped pits (V-pits) in InGaN/GaN multiple-quantum-well (MQW) solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths for the photo-generated carriers. Due to the thin barrier thickness and low indium composition of the MQW on V-pit sidewall, the carriers entered the sidewall QWs can easily escape and contribute to the photocurrent. This forms a parallel escape route for the carries generated in the fiat quantum wells. As the barrier thickness of the fiat MQW increases, more carriers would transport via the V-pits. Furthermore, it is found that the V-pits may reduce the recombination losses of carriers due to their screening effect to the dislocations. These discoveries are not only helpful for understanding the carrier transport mechanism in the InGaN/GaN MQW, but also important in design of the structure of solar cells.展开更多
In this paper,to better reveal the surface effect and the screening effect as well as the nonlinear multi-field coupling characteristic of the multifunctional piezoelectric semiconductor(PS)nanodevice,and to further i...In this paper,to better reveal the surface effect and the screening effect as well as the nonlinear multi-field coupling characteristic of the multifunctional piezoelectric semiconductor(PS)nanodevice,and to further improve its working performance,a magneto-mechanical-thermo coupling theoretical model is theoretically established for the extensional analysis of a three-layered magneto-electro-semiconductor coupling laminated nanoplate with the surface effect.Next,by using the current theoretical model,some numerical analyses and discussion about the surface effect,the corresponding critical thickness of the nanoplate,and the distributions of the physical fields(including the electron concentration perturbation,the electric potential,the electric field,the average electric displacement,the effective polarization charge density,and the total charge density)under different initial state electron concentrations,as well as their active manipulation via some external magnetic field,pre-stress,and temperature stimuli,are performed.Utilizing the nonlinear multi-field coupling effect induced by inevitable external stimuli in the device operating environment,this paper not only provides theoretical support for understanding the size-dependent tuning/controlling of carrier transport as well as its screening effect,but also assists the design of a series of multiferroic PS nanodevices.展开更多
The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to th...The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to the phase transition of BaF2 nanocrystals under high pressure. The charge carriers in BaF2 nanocrystals include both Fions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge-discharge processes in the Fm3m phase more difficult.展开更多
Organic light-emitting diodes(OLEDs)have demonstrated remarkable advancements in both device lifetime and luminous efficiency.However,insufficient operation lifetime due to device degradation remains a major hurdle,es...Organic light-emitting diodes(OLEDs)have demonstrated remarkable advancements in both device lifetime and luminous efficiency.However,insufficient operation lifetime due to device degradation remains a major hurdle,especially for brighter devices.Understanding the degradation mechanisms of OLEDs due to the degradation of functional materials and the formation of defects in device architectures continues to be a significant challenge.Herein,we evaluate the degradation characteristics by scrutinizing the electrical and optical properties,as well as analyzing the charge carrier dynamics in pristine and aged states of phosphorescent OLEDs(PhOLEDs).We show that degradation mechanisms in PhOLEDs can be elucidated in terms of the ideality factors of current and luminance in pristine and aged device states.The consistent shifts in distinct ideality factors across various states points out that the device degradation is attributed to the deterioration of the guest material,i.e.green-light-emitting phosphorescent material.Conversely,the incongruity in ideality factor changes between the two states indicates that the degradation results from the deterioration of non-light-emitting material.Subsequent characterization experiments provide further evidence that this degradation is primarily attributed to the deterioration of CBP-host material.The thorough understanding of degradation mechanisms established in this study can contribute to realizing the highly reliable PhOLEDs with a long lifetime.展开更多
Perovskite solar cells(PSCs) have raised research interest in scientific community because their power conversion efficiency is comparable to that of traditional commercial solar cells(i.e., amorphous Si, GaAs,and CdT...Perovskite solar cells(PSCs) have raised research interest in scientific community because their power conversion efficiency is comparable to that of traditional commercial solar cells(i.e., amorphous Si, GaAs,and CdTe). Apart from that, PSCs are lightweight, are flexible, and have low production costs. Recently, graphene has been used as a novel material for PSC applications due to its excellent optical, electrical, and mechanical properties. The hydrophobic nature of graphene surface can provide protection against air moisture from the surrounding medium, which can improve the lifetime of devices. Herein, we review recent developments in the use of graphene for PSC applications as a conductive electrode,carrier transporting material, and stabilizer material. By exploring the application of graphene in PSCs, a new class of strategies can be developed to improve the device performance and stability before it can be commercialized in the photovoltaic market in the near future.展开更多
A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to exten...A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical (QM) effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.展开更多
Quantum dots(QDs)are promising candidates for the next-generation optical and electronic devices due to the outstanding photoluminance efficiency,tunable bandgap and facile solution synthesis.Nevertheless,the limited ...Quantum dots(QDs)are promising candidates for the next-generation optical and electronic devices due to the outstanding photoluminance efficiency,tunable bandgap and facile solution synthesis.Nevertheless,the limited optoelectronic performance and poor lifetime of QDs devices hinder their further applications.As a gas-phase surface treatment method,atomic layer deposition(ALD)has shown the potential in QDs surface modification and device construction owing to the atomic-level control and excellent uniformity/conformality.In this perspective,the attempts to utilize ALD techniques in QDs modification to improve the photoluminance efficiency,stability,carrier mobility,as well as interfacial carrier utilization are introduced.ALD proves to be successful in the photoluminance quantum yield(PLQY)enhancement due to the elimination of QDs surface dangling bonds and defects.The QDs stability and devices lifetime are improved greatly through the introduction of ALD barrier layers.Furthermore,the carrier transport is ameliorated efficiently by infilling interstitial spaces during ALD process.Attributed to the ultra-thin and dense coating on the interface,the improvement on optoelectronic performance is achieved.Finally,the challenges of ALD applications in QDs at present and several prospects including ALD process optimization,in-situ characterization and computational simulations are proposed.展开更多
Perovskite solar cell has emerged as a promising candidate in flexible electronics due to its high mechanical flexibility,excellent optoelectronic properties,light weight and low cost.With the rapid development of the...Perovskite solar cell has emerged as a promising candidate in flexible electronics due to its high mechanical flexibility,excellent optoelectronic properties,light weight and low cost.With the rapid development of the device structure and materials processing,the flexible perovskite solar cells(FPSCs)deliver 21.1%power conversion efficiency.This review introduces the latest developments in the efficiency and stability of FPSCs,including flexible substrates,carrier transport layers,perovskite films and electrodes.Some suggestions on how to further improve the efficiency,environmental and mechanical stability of FPSCs are provided.Specifically,we considered that to elevate the performance of FPSCs,it is crucial to substantially improve film quality of each functional layer,develop more boost encapsulation approach and explore flexible transparent electrodes with high conductivity,transmittance,low cost and expandable processability.展开更多
Nanocrystalline Ge (nc-Ge) single layers and nc-Ge/SiNx multilayers are prepared by laser annealing amorphous Ge (a-Ge) films and a-Ge/SiNx multilayers. The microstructures as well as the electrical properties of ...Nanocrystalline Ge (nc-Ge) single layers and nc-Ge/SiNx multilayers are prepared by laser annealing amorphous Ge (a-Ge) films and a-Ge/SiNx multilayers. The microstructures as well as the electrical properties of laser-crystallized samples are systematically studied by using various techniques. It is found that the optical band gap of nc-Ge film is reduced compared with its amorphous counterpart. The formed nc-Ge film is of p-type, and the dark conductivity is enhanced by 6 orders for an nc-Ge single layer and 4 orders for a multilayer. It is suggested that the carrier transport mechanism is dominant by the thermally activation process via the nanocrystal, which is different from the thermally annealed nc-Ge sample at an intermediate temperature. The carrier mobility of nc-Ge film can reach as high as about 39.4 cm2.V ^-1 .s^-1, which indicates their potential applications in future nano-devices.展开更多
The strong anisotropic electrical properties of one-dimensional(1 D) nanostructure semiconductors,especially the anisotropic carrier transport, have a negative and significant influence on the performance of solar cel...The strong anisotropic electrical properties of one-dimensional(1 D) nanostructure semiconductors,especially the anisotropic carrier transport, have a negative and significant influence on the performance of solar cells if the nanostructures have random orientation. Considering the advantages of nanorod solar cells in carrier transport, we have achieved growth of vertically aligned Sb_(2)Se_(3) nanorod array with highly(hk1) orientation on Cd S substrate, and constructed superstrate nanorod solar cells for the first time. The Sb_(2)Se_(3) nanorod array solar cells exhibit the more efficient and long-range carrier transport in vertical direction. Furthermore, in order to suppress interface recombination, a CuInSe_(2) quantum dots(QDs) sensitizer has been applied to fill the volume between the nanorods completely, thus forming an interpenetrating nanocomposite structure. The CuInSe_(2) QDs can harvest additional light by absorption of visible light and contribute photocurrent. Meantime, the QDs function as a hole transport material and thus reduce the dependence of lateral transport. Consequently, the interpenetrating nanocomposite CuInSe_(2) / Sb_(2)Se_(3) solar cells display a power conversion efficiency of 7.54% with significant enhancements in the short-circuit current density and open-circuit voltage over pure Sb_(2)Se_(3) nanorod cells. This is the highest efficiency for superstrate solar cells based on Sb_(2)Se_(3) nanorod arrays.展开更多
The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found tha...The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.展开更多
In our experiment, an atomic layer MoS2structure grown on SiO2/Si substrates is used in transport test. The voltage U14,23 oscillates and the corresponding period varies with applied current. The largest period appear...In our experiment, an atomic layer MoS2structure grown on SiO2/Si substrates is used in transport test. The voltage U14,23 oscillates and the corresponding period varies with applied current. The largest period appears at 45 μA. The oscillation periods are different when samples are under laser radiation or in darkness. We discover that under the laser irradiation, the oscillation period occurs at lower current than in the darkness case. Meanwhile, the drift velocity is estimated at ~10~7 cm/s. Besides, by studying the envelope of U14,23 versus applied current, we see a beating phenomenon at a certain current value. The beating period in darkness is larger than under laser irradiation. The difference between beating periods reveals the energy difference of electrons. Similar results are obtained by using different laser power densities and different light sources. The possible mechanism behind the oscillation period is discussed.展开更多
We demonstrate a two-dimensional(2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the bounda...We demonstrate a two-dimensional(2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the boundary by solving self-consistently the 2D Poisson and Boltzmann transport equations(BTE).The infrastructure of this simulator,including the energy bands obtained from the empirical pseudo potential method,various scattering mechanics employed,and the appropriate treatment of the carrier transport at the boundary between two different semiconductor materials,is also described.As verification and calibration,we have performed a simulation on two types of silicon-germanium(Si-Ge) heterojunctions with different doping profiles—the p-p homogeneous type and the n-p inhomogeneous type.The current-voltage characteristics are simulated,and the distributions of potential and carrier density are also plotted,which show the validity of our simulator.展开更多
All-solid-state Li-SeS_(2) batteries(ASSLSs)are more attractive than traditional liquid Li-ion batteries due to superior thermal stability and higher energy density.However,various factors limit the practical applicat...All-solid-state Li-SeS_(2) batteries(ASSLSs)are more attractive than traditional liquid Li-ion batteries due to superior thermal stability and higher energy density.However,various factors limit the practical application of all-solid-state Li-SeS_(2) batteries,such as the low ionic conductivity of the solid-state electrolyte and the poor kinetic property of the cathode composite,resulting in unsatisfactory rate capability.Here,we employed a traditional ball milling method to design a Li_(7)P_(2.9)W_(0.05)S_(10.85) glass–ceramic electrolyte with high conductivity of 2.0 mS cm^(−1) at room temperature.In order to improve the kinetic property,an interpenetrating network strategy is proposed for rational cathode composite design.Signifcantly,the disordered cathode composite with an interpenetrating network could promote electronic and ionic conduction and intimate contacts between the electrolyte–electrode particles.Moreover,the tortuosity factor of the carrier transport channel is considerably reduced in electrode architectures,leading to superior kinetic performance.Thus,assembled ASSLS exhibited higher capacity and better rate capability than its counterpart.This work demonstrates that an interpenetrating network is essential for improving carrier transport in cathode composite for high rate all-solid-state Li-SeS_(2) batteries.展开更多
Lead chalcogenide colloidal quantum dots(CQDs)are regarded as attractive absorption materials for novel solar cells(SCs).The cost of lead chalcogenide CQD has been decreased to a commercialization target of$5/g due to...Lead chalcogenide colloidal quantum dots(CQDs)are regarded as attractive absorption materials for novel solar cells(SCs).The cost of lead chalcogenide CQD has been decreased to a commercialization target of$5/g due to the direct production of CQD inks.However,the photoelectric conversion efficiency(PCE)of lead chalcogenide CQDSCs is presently close to 14%,well below the commercialization target(20%),which is only 41%of the theoretical Shockley-Queisser limit efficiency.In this study,the different losses of open-circuit voltage(V_(oc)),fill factor(FF),and short circuit current density(J_(sc))for current CQDSCs are systematically discussed,as well as the percentage and likely causes of each loss.Then the primary reasons for the CQDSCs’performance constraints are highlighted.Following that,we focus on the CQDSCs interfaces(i.e.,CQD/CQD,CQD/HTL,and ETL/CQD)and explore viable ways to reduce device performance loss.Finally,based on the discussion above,we propose many enhancements to significantly solve numerous major obstacles impeding device performance to boost the PCE of CQDSCs for future commercialization significantly.展开更多
基金financially supported by the National Key Research and Development Program of China(2022YFE0118400)the National Natural Science Foundation of China(51702038)+1 种基金the Science&Technology Department of Sichuan Province(2020YFG0061)the Recruitment Program for Young Professionals。
文摘Quasi-2D Dion-Jacobson(DJ)tin halide perovskite has attracted much attention due to its elimination of Van der Waals gap and enhanced environmental stability.However,the bulky organic spacers usually form a natural quantum well structure,which brings a large quantum barrier and poor film quality,further limiting the carrier transport and device performance.Here,we designed three organic spacers with different chain lengths(ethylenediamine(EDA),1,3-propanediamine(PDA),and 1,4-butanediamine(BDA))to investigate the quantum barrier dependence.Theoretical and experimental characterizations indicate that EDA with short chain can reduce the lattice distortion and dielectric confinement effect,which is beneficial to the effective dissociation of excitons and the inhibition of trap-free non-radiative relaxation.In addition,EDA cation shows strong interaction with the inorganic octahedron,realizing large aggregates in precursor solution and high-quality films with improved structural stability.Furthermore,femtosecond transient absorption proves that EDA cations can also weaken the formation of small n-phases with large quantum barrier to achieve effective carrier transport between different nphases.Finally,the quasi-2D DJ(EDA)FA_(9)Sn_(10)I_(31)solar cells achieves a 7.07%power conversion efficiency with good environment stability.Therefore,this work sheds light on the regulation of the quantum barrier and carrier transport through the chain length of organic spacer for qua si-2D DJ lead-free perovskites.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60606013)the National Basic Research Program of China (Grant No. 2006CB302705)
文摘Interface roughness strongly influences the performance of germanium metal-organic-semiconductor field effect transistors (MOSFETs). In this paper, a 2D full-band Monte Carlo simulator is used to study the impact of interface roughness scattering on electron and hole transport properties in long- and short- channel Ge MOSFETs inversion layers. The carrier effective mobility in the channel of Ge MOSFETs and the in non-equilibriurn transport properties are investigated. Results show that both electron and hole mobility are strongly influenced by interface roughness scattering. The output curves for 50 nm channel-length double gate n and p Ge MOSFET show that the drive currents of n- and p-Ge MOSFETs have significant improvement compared with that of Si n- and p-MOSFETs with smooth interface between channel and gate dielectric. The 82% and 96% drive current enhancement are obtained for the n- and p-MOSFETs with the completely smooth interface. However, the enhancement decreases sharply with the increase of interface roughness. With the very rough interface, the drive currents of Ge MOSFETs are even less than that of Si MOSFETs. Moreover, the significant velocity overshoot also has been found in Ge MOSFETs.
基金supported by the National Natural Science Foundations of China(Nos.51872228,U2032170 and 51802262)the National Key Research and Development Program of China(2016YFE0115200 and 2016YFF0101301)+2 种基金the Natural Science Foundations of Shaanxi Province(2019JQ-459 and 2020JC-12)the Natural Science Basic Research Plan in Shaanxi Province of China(2019ZDLGY04-07)the Fundamental Research Funds for the Central Universities(D5000210906 and 3102020QD0408)。
文摘All-inorganic Cs_(3)Bi_(2)I_(9)(CBI)halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability.Unfortunately,the discrete molecular[Bi2I9]3−clusters limit the charge-transport behaviors.Herein,the defect halide perovskite based on trivalent Bi^(3+)is expanded to Cs_(3)Bi_(2)I_(6)Br_(3)(CBIB).Centimeter-size CBIB single crystal(Φ15×70 mm^(3))was grown by the vertical Bridgeman method.The powder X-ray diffraction analysis shows that CBIB has structure with lattice parameters of a=b=8.223Å,c=10.024Å,α=β=90°andγ=120°.The density functional theory(DFT)calculations demonstrate that the charge density distribution was enhanced after the dimensional expansion.The enhancement of carrier transport ability of(00l)in-plane is characterized before and after dimensional improvement.The obtained CBIB(001)exhibited an electron mobility up to 40.03 cm^(2)V^(−1)s^(−1)by time-of-flight(TOF)technique,higher than 26.46 cm^(2)V^(−1)s^(−1)of CBI(001).Furthermore,the X-ray sensitivity increases from 707.81μC Gy^(−1)cm^(−2)for CBI(001)to 3194.59μC Gy−1 cm^(−2)for CBIB(001).This research will deepen our understanding of Bi-based perovskite materials and afford more promising strategies for lead-free perovskite optoelectronic devices modification.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11574362,61210014,and 11374340the Innovative Clean-Energy Research and Application Program of Beijing Municipal Science and Technology Commission under Grant No Z151100003515001
文摘The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.
基金Funded by the National Natural Science Foundation of China(Nos.51202063 and 51177003)Hubei Provincial Department of Education(No.Q20111009)
文摘We established a model for investigating polycrystalline silicon(poly-Si) thin film transistors(TFTs).The effect of grain boundaries(GBs) on the transfer characteristics of TFT was analyzed by considering the number and the width of grain boundaries in the channel region,and the dominant transport mechanism of carrier across grain boundaries was subsequently determined.It is shown that the thermionic emission(TE) is dominant in the subthreshold operating region of TFT regardless of the number and the width of grain boundary.To a poly-Si TFT model with a 1 nm-width grain boundary,in the linear region,thermionic emission is similar to that of tunneling(TU),however,with increasing grain boundary width and number,tunneling becomes dominant.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61564007 and 11364034)the Sci-Tech Support Plan of Jiangxi Province,China(Grant No.20141BBE50035)
文摘Carrier transport via the V-shaped pits (V-pits) in InGaN/GaN multiple-quantum-well (MQW) solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths for the photo-generated carriers. Due to the thin barrier thickness and low indium composition of the MQW on V-pit sidewall, the carriers entered the sidewall QWs can easily escape and contribute to the photocurrent. This forms a parallel escape route for the carries generated in the fiat quantum wells. As the barrier thickness of the fiat MQW increases, more carriers would transport via the V-pits. Furthermore, it is found that the V-pits may reduce the recombination losses of carriers due to their screening effect to the dislocations. These discoveries are not only helpful for understanding the carrier transport mechanism in the InGaN/GaN MQW, but also important in design of the structure of solar cells.
基金supported by the National Natural Science Foundation of China(Nos.12072253,11972176,and 12062011)the Doctoral Science Fund of Lanzhou University of Technology of China(No.062002)the Opening Project from the State Key Laboratory for Strength and Vibration of Mechanical Structures of China(No.SV2021-KF-19)。
文摘In this paper,to better reveal the surface effect and the screening effect as well as the nonlinear multi-field coupling characteristic of the multifunctional piezoelectric semiconductor(PS)nanodevice,and to further improve its working performance,a magneto-mechanical-thermo coupling theoretical model is theoretically established for the extensional analysis of a three-layered magneto-electro-semiconductor coupling laminated nanoplate with the surface effect.Next,by using the current theoretical model,some numerical analyses and discussion about the surface effect,the corresponding critical thickness of the nanoplate,and the distributions of the physical fields(including the electron concentration perturbation,the electric potential,the electric field,the average electric displacement,the effective polarization charge density,and the total charge density)under different initial state electron concentrations,as well as their active manipulation via some external magnetic field,pre-stress,and temperature stimuli,are performed.Utilizing the nonlinear multi-field coupling effect induced by inevitable external stimuli in the device operating environment,this paper not only provides theoretical support for understanding the size-dependent tuning/controlling of carrier transport as well as its screening effect,but also assists the design of a series of multiferroic PS nanodevices.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11374131,11674404,11404137 and 61378085the Program for New Century Excellent Talents in University under Grant No NCET-13-0824+1 种基金the Program for the Development of Science and Technology of Jilin Province under Grant Nos 201201079 and 20150204085GXthe Twentieth Five-Year Program for Science and Technology of Education Department of Jilin Province under Grant No 20150221
文摘The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to the phase transition of BaF2 nanocrystals under high pressure. The charge carriers in BaF2 nanocrystals include both Fions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge-discharge processes in the Fm3m phase more difficult.
基金he National Research Foundation of Korea(NRF)grant funded by the Korean Government(2020R1A2C3003958)the Basic Science Research Program(Priority Research Institute)through the NRF grant funded by the Ministry of Education(2021R1A6A1A10039823)the Korea Basic Science Institute(National Research Facilities and Equipment Center)grant funded by the Ministry of Education(2020R1A6C101B194).
文摘Organic light-emitting diodes(OLEDs)have demonstrated remarkable advancements in both device lifetime and luminous efficiency.However,insufficient operation lifetime due to device degradation remains a major hurdle,especially for brighter devices.Understanding the degradation mechanisms of OLEDs due to the degradation of functional materials and the formation of defects in device architectures continues to be a significant challenge.Herein,we evaluate the degradation characteristics by scrutinizing the electrical and optical properties,as well as analyzing the charge carrier dynamics in pristine and aged states of phosphorescent OLEDs(PhOLEDs).We show that degradation mechanisms in PhOLEDs can be elucidated in terms of the ideality factors of current and luminance in pristine and aged device states.The consistent shifts in distinct ideality factors across various states points out that the device degradation is attributed to the deterioration of the guest material,i.e.green-light-emitting phosphorescent material.Conversely,the incongruity in ideality factor changes between the two states indicates that the degradation results from the deterioration of non-light-emitting material.Subsequent characterization experiments provide further evidence that this degradation is primarily attributed to the deterioration of CBP-host material.The thorough understanding of degradation mechanisms established in this study can contribute to realizing the highly reliable PhOLEDs with a long lifetime.
基金financially supported by the Ministry of Higher Education (FRGS/1/2017/STG02/UKM/02/1)Universiti Kebangsaan Malaysia (GUP-2015-019)
文摘Perovskite solar cells(PSCs) have raised research interest in scientific community because their power conversion efficiency is comparable to that of traditional commercial solar cells(i.e., amorphous Si, GaAs,and CdTe). Apart from that, PSCs are lightweight, are flexible, and have low production costs. Recently, graphene has been used as a novel material for PSC applications due to its excellent optical, electrical, and mechanical properties. The hydrophobic nature of graphene surface can provide protection against air moisture from the surrounding medium, which can improve the lifetime of devices. Herein, we review recent developments in the use of graphene for PSC applications as a conductive electrode,carrier transporting material, and stabilizer material. By exploring the application of graphene in PSCs, a new class of strategies can be developed to improve the device performance and stability before it can be commercialized in the photovoltaic market in the near future.
基金Project supported by the Special Foundation for State Major Basic Research Program of China (Grant No G2000035602) and the National Natural Science Foundation of China (Grant No 90307006).
文摘A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical (QM) effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.
文摘Quantum dots(QDs)are promising candidates for the next-generation optical and electronic devices due to the outstanding photoluminance efficiency,tunable bandgap and facile solution synthesis.Nevertheless,the limited optoelectronic performance and poor lifetime of QDs devices hinder their further applications.As a gas-phase surface treatment method,atomic layer deposition(ALD)has shown the potential in QDs surface modification and device construction owing to the atomic-level control and excellent uniformity/conformality.In this perspective,the attempts to utilize ALD techniques in QDs modification to improve the photoluminance efficiency,stability,carrier mobility,as well as interfacial carrier utilization are introduced.ALD proves to be successful in the photoluminance quantum yield(PLQY)enhancement due to the elimination of QDs surface dangling bonds and defects.The QDs stability and devices lifetime are improved greatly through the introduction of ALD barrier layers.Furthermore,the carrier transport is ameliorated efficiently by infilling interstitial spaces during ALD process.Attributed to the ultra-thin and dense coating on the interface,the improvement on optoelectronic performance is achieved.Finally,the challenges of ALD applications in QDs at present and several prospects including ALD process optimization,in-situ characterization and computational simulations are proposed.
文摘Perovskite solar cell has emerged as a promising candidate in flexible electronics due to its high mechanical flexibility,excellent optoelectronic properties,light weight and low cost.With the rapid development of the device structure and materials processing,the flexible perovskite solar cells(FPSCs)deliver 21.1%power conversion efficiency.This review introduces the latest developments in the efficiency and stability of FPSCs,including flexible substrates,carrier transport layers,perovskite films and electrodes.Some suggestions on how to further improve the efficiency,environmental and mechanical stability of FPSCs are provided.Specifically,we considered that to elevate the performance of FPSCs,it is crucial to substantially improve film quality of each functional layer,develop more boost encapsulation approach and explore flexible transparent electrodes with high conductivity,transmittance,low cost and expandable processability.
基金Project supported by the National Basic Research Program of China (Grant No.2013CB632101)the National Natural Science Foundation of China (Grant Nos.11274155 and 61036001)Priority Academic Program Development of Jiangsu Higher Education Institutions,Jiangsu Province,China
文摘Nanocrystalline Ge (nc-Ge) single layers and nc-Ge/SiNx multilayers are prepared by laser annealing amorphous Ge (a-Ge) films and a-Ge/SiNx multilayers. The microstructures as well as the electrical properties of laser-crystallized samples are systematically studied by using various techniques. It is found that the optical band gap of nc-Ge film is reduced compared with its amorphous counterpart. The formed nc-Ge film is of p-type, and the dark conductivity is enhanced by 6 orders for an nc-Ge single layer and 4 orders for a multilayer. It is suggested that the carrier transport mechanism is dominant by the thermally activation process via the nanocrystal, which is different from the thermally annealed nc-Ge sample at an intermediate temperature. The carrier mobility of nc-Ge film can reach as high as about 39.4 cm2.V ^-1 .s^-1, which indicates their potential applications in future nano-devices.
基金financially supported by the National Key R&D Program of China (Grant No. 2019YFB1503400)the National Natural Science Foundation of China (Grant No. 61804064)the Natural Science Foundation of Guangdong Province (Grant No.2019A1515011616)。
文摘The strong anisotropic electrical properties of one-dimensional(1 D) nanostructure semiconductors,especially the anisotropic carrier transport, have a negative and significant influence on the performance of solar cells if the nanostructures have random orientation. Considering the advantages of nanorod solar cells in carrier transport, we have achieved growth of vertically aligned Sb_(2)Se_(3) nanorod array with highly(hk1) orientation on Cd S substrate, and constructed superstrate nanorod solar cells for the first time. The Sb_(2)Se_(3) nanorod array solar cells exhibit the more efficient and long-range carrier transport in vertical direction. Furthermore, in order to suppress interface recombination, a CuInSe_(2) quantum dots(QDs) sensitizer has been applied to fill the volume between the nanorods completely, thus forming an interpenetrating nanocomposite structure. The CuInSe_(2) QDs can harvest additional light by absorption of visible light and contribute photocurrent. Meantime, the QDs function as a hole transport material and thus reduce the dependence of lateral transport. Consequently, the interpenetrating nanocomposite CuInSe_(2) / Sb_(2)Se_(3) solar cells display a power conversion efficiency of 7.54% with significant enhancements in the short-circuit current density and open-circuit voltage over pure Sb_(2)Se_(3) nanorod cells. This is the highest efficiency for superstrate solar cells based on Sb_(2)Se_(3) nanorod arrays.
基金Project supported by the State Key Program of National Natural Science of China (Grant Nos 10474056 and 10574082)the Natural Science Foundation of Shandong Province (Grant No Z2005A01)
文摘The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.
基金Project supported by the Zhejiang Provincial Natural Science Foundation,China(Grant Nos.LY16F040003 and LY16A040007)the National Natural Science Foundation of China(Grant Nos.51401069 and 11204058)
文摘In our experiment, an atomic layer MoS2structure grown on SiO2/Si substrates is used in transport test. The voltage U14,23 oscillates and the corresponding period varies with applied current. The largest period appears at 45 μA. The oscillation periods are different when samples are under laser radiation or in darkness. We discover that under the laser irradiation, the oscillation period occurs at lower current than in the darkness case. Meanwhile, the drift velocity is estimated at ~10~7 cm/s. Besides, by studying the envelope of U14,23 versus applied current, we see a beating phenomenon at a certain current value. The beating period in darkness is larger than under laser irradiation. The difference between beating periods reveals the energy difference of electrons. Similar results are obtained by using different laser power densities and different light sources. The possible mechanism behind the oscillation period is discussed.
基金Project supported by the National Fundamental Basic Research Program of China(No.2006CB302705)the Foundation for Key Program Project of Chinese Ministry of Education(No.107003).
文摘We demonstrate a two-dimensional(2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the boundary by solving self-consistently the 2D Poisson and Boltzmann transport equations(BTE).The infrastructure of this simulator,including the energy bands obtained from the empirical pseudo potential method,various scattering mechanics employed,and the appropriate treatment of the carrier transport at the boundary between two different semiconductor materials,is also described.As verification and calibration,we have performed a simulation on two types of silicon-germanium(Si-Ge) heterojunctions with different doping profiles—the p-p homogeneous type and the n-p inhomogeneous type.The current-voltage characteristics are simulated,and the distributions of potential and carrier density are also plotted,which show the validity of our simulator.
基金This work is supported by the National Natural Science Foundation of China(No.21975025,21203008,51772030)the National Key Research and Development Program of China“New Energy Project for Electric Vehicle”(No.2016YFB0100204)+1 种基金the Nature Science Foundation of Beijing Municipality(No.2172051)State Key Laboratory also funds the project for Modifcation of Chemical Fibers and Polymer Materials,Donghua University.DTA,XRD,XPS,and NMR measurements were performed in the Analysis&Testing Center,Beijing Institute of Technology。
文摘All-solid-state Li-SeS_(2) batteries(ASSLSs)are more attractive than traditional liquid Li-ion batteries due to superior thermal stability and higher energy density.However,various factors limit the practical application of all-solid-state Li-SeS_(2) batteries,such as the low ionic conductivity of the solid-state electrolyte and the poor kinetic property of the cathode composite,resulting in unsatisfactory rate capability.Here,we employed a traditional ball milling method to design a Li_(7)P_(2.9)W_(0.05)S_(10.85) glass–ceramic electrolyte with high conductivity of 2.0 mS cm^(−1) at room temperature.In order to improve the kinetic property,an interpenetrating network strategy is proposed for rational cathode composite design.Signifcantly,the disordered cathode composite with an interpenetrating network could promote electronic and ionic conduction and intimate contacts between the electrolyte–electrode particles.Moreover,the tortuosity factor of the carrier transport channel is considerably reduced in electrode architectures,leading to superior kinetic performance.Thus,assembled ASSLS exhibited higher capacity and better rate capability than its counterpart.This work demonstrates that an interpenetrating network is essential for improving carrier transport in cathode composite for high rate all-solid-state Li-SeS_(2) batteries.
基金supported by the Japan Science and Technology Agency(JST)Mirai program(JPMJMI17EA)MEXT KAKENHI(Grant Nos.26286013,and 17H02736)。
文摘Lead chalcogenide colloidal quantum dots(CQDs)are regarded as attractive absorption materials for novel solar cells(SCs).The cost of lead chalcogenide CQD has been decreased to a commercialization target of$5/g due to the direct production of CQD inks.However,the photoelectric conversion efficiency(PCE)of lead chalcogenide CQDSCs is presently close to 14%,well below the commercialization target(20%),which is only 41%of the theoretical Shockley-Queisser limit efficiency.In this study,the different losses of open-circuit voltage(V_(oc)),fill factor(FF),and short circuit current density(J_(sc))for current CQDSCs are systematically discussed,as well as the percentage and likely causes of each loss.Then the primary reasons for the CQDSCs’performance constraints are highlighted.Following that,we focus on the CQDSCs interfaces(i.e.,CQD/CQD,CQD/HTL,and ETL/CQD)and explore viable ways to reduce device performance loss.Finally,based on the discussion above,we propose many enhancements to significantly solve numerous major obstacles impeding device performance to boost the PCE of CQDSCs for future commercialization significantly.