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In recent years, transition metal-nitrogen-carbon (M-N-C) composites are expected to be an alternative to platinum group metal (PGM) among various nonprecious metal catalysts investigated. However, the major challenge comes from insufficient electrocatalytic performance and durability for oxygen reduction reaction (ORR). In addition to the selection of suitable central metal active sites, the electrocatalytic activity and stability of the M-N-C catalysts can be enhanced by adjusting the electronic structure of the catalysts. In this work, M-N-C/F composites were synthesized by loading transition metal phthalocyanine complexes onto pre-fluorinated carbon nanotubes through a simple pyrolysis method. Pyrroline-N(PN) and graphite-N(GN) formed after thermal treatment can act as electron acceptors to modulate their charge distribution on the M-N4 sites, and the use of pre-fluorinated nanotubes also allows for a more controlled introduction of fluoride ions that are well coordinated to transition metals, both of which can modulate and modify the electronic structure of M-N-C catalysts. The obtained manganese phthalocyanine/fluorinated carbon nanotubes at 800°C (MnPc/FCNT800) exhibits a competitive electrocatalytic ORR performance with the half-wave potential (E1/2) of 0.9 V and only 12.1% decay after 20 h long-term chronoamperometry (CA) test in 1.0 M KOH electrolyte, outperforming the commercial Pt/C. Overall, this work paves the way of the electronic structure modification and design of such M-N-C composites for sustainable energy applications.

In this paper, nanocones array is introduced into bottom silicon cells design. By finite-difference time-domain methods, the absorption efficiency in the range of 300-1100nm has been analyzed, and the structural parameters have been also optimized. Our calculations show that with the increase of the height of the nanocones, the spectra of the top cell and the bottom cell have significant interference effects, and the short wave photons and long wave photons can achieve the maximum light absorption through strict optical management.The absorption enhancement modes of photons at different wavelengths have been analyzed intuitively by the distribution of electric field. These results enable a viable and convenient route toward high efficiency design of perovskite/Si tandem solar cells.

Perovskite solar cells are used in silicon-based tandem solar cells due to their tunable band gap, high absorption coefficient and low preparation cost. However, the relatively large optical refractive index of bottom silicon, in comparison with that of top perovskite absorber layers, results in significant reflection losses in two-terminal devices. Therefore, light management is crucial to improve photocurrent absorption in the Si bottom cell. In this paper, nanoholes array filled with TiO2 is introduced into bottom cells design. By finite-difference time-domain methods, the absorption efficiency and photocurrent density in the range of 300–1100 nm has been analyzed, and the structural parameters have been also optimized. Our calculations show the photocurrent density which tends to be saturated with the increase in the height of the nanoholes. The absorption enhancement modes of photons at different wavelengths have been analyzed intuitively by the distribution of electric field. These results enable a viable and convenient route toward high efficiency design of perovskite/Si tandem solar cells.

Perovskite solar cells have attracted great attention in recent years due to its advantageous features including low production cost. Incorporation of plasmonic metal nanocrystals is a promising approach for broadening and enhancing the light harvesting of Perovskite solar cells. In this paper, we report a facile and versatile route to tune the photoresponse of perovskite via embedding Ag nanorods with multiplexed length-to-diameter aspect ratios. Plasmonic Ag nanorods with length-to-diameter aspect ratio of 2 and 3 are embedded, exhibiting their plasmon peak at 789 nm and 798 nm, respectively. Furthermore, the mechanism of the absorption has been discussed.

Using the density functional theory combined with the Keldysh non-equilibrium Green's function methods, we investigate the thermally (or voltage)-induced spin transport properties of a two-probe device consisting of a carbon atom chain sandwiched between two zigzag graphene nanoribbon (ZGNR) electrodes. When the edge of one ZGNR electrode is partially doped by B atoms, the flowing direction of thermal single-spin current can be reversed in contrast with the undoped case. In addition, when a voltage is applied across the carbon-based device at room temperature, a giant rectification ratio of 10 4 is observed which mainly originates from the band-structure incompatibility between two ZGNR electrodes in the voltage window. Moveover, in the high-voltage region, a single-spin negative differential resistance is also observed in the carbon-based device. Our findings here suggest that the carbon-based systems can be used to design spintronic devices with multiple functions.

Using first-principles methods, we have investigated magnetic properties and thermospin effects of zigzag silicene nanoribbons (ZSiNRs) absorbed by a single Si atom. After a relaxation, a steady dumbbell-like structure is formed, which induces a weaker antiferromagnetic (AFM) coupling between two zigzag edges. Therefore, a band gap is opened, meanwhile the adsorbed ZSiNRs show a spin semiconducting property. A large spin thermopower and weak charge thermopower in adsorbed ZSiNR-based devices can be simultaneously achieved, which is attributed to a nearly perfect mirror symmetry of spin-up and spin-down transmission spectra relative to the Fermi level.

Recently, a holey two-dimensional (2D) C2N crystal with a wide band gap has been successfully synthesized. However, its non-magnetic property largely limits real applications in spintronics. Here we find that edge magnetism can be introduced by tailoring the holey 2D C2N crystal into nanoribbons with zigzag edges. When edge N atoms are bare or passivated by H atoms, the device can be used to design high-performance thermospin devices and thermal rectifiers. This is ascribed to the emergence of a spin semiconducting property with a wide band gap. Moreover, if the edge N atoms are passivated by O atoms, the device shows a half-metallic property; meanwhile an obvious spin Seebeck effect can also be observed when a temperature difference is applied across the device.

The theoretical limit photoelectric conversion efficiency of the new perovskite/silicon-based tandem solar cell can reach 42%, which has attracted wide attention due to its wide spectral response and low preparation cost. At present, the optical loss of the mechanical stack is large, so the optical design of the laminated battery is crucial. In this paper, perovskite/silicon-based laminated cells with backplate grating structure are used as models to analyze the optical absorption characteristics of stacked battery by FDTD. The results show that the parameters such as the period and height of the backplane grating structure are effective in improving absorption of long wavelength photons in bottom cells, which provides a theoretical basis for the further design of a new perovskite/silicon-based laminate battery.

The possibility to improve thermoelectric performance of carbon-based quantum devices is of fundamental and importance in the fields of energy conservation, environmental protection, and green energy. Here we propose an effective avenue to enhance the thermoelectric figure of merits (TE-FOMs) of an all-carbon quantum device with the help of first-principles methods, and the device is constructed by a zigzag-edged trigonal graphene (ZTG) connected with zigzag-edged graphene nanoribbons (ZGNR) electrodes through the carbon atomic chains (CACs). Using a gate field, the spin-up transmission peak can be tuned from the position below the Fermi level to that above the Fermi level. However, the position of the spin-down transmission peak above the Fermi level is insensitive to the gate field. Therefore, the device can be converted from the p type to n type for the spin-up component by a gate field, while for the spin-down component the device remains n type. Meanwhile, we also find that the charge (spin) TE-FOMs at the Fermi level can be increased to about eight (three) times as compared with the case in the absence of the gate field. These TE-FOMs can also be significantly improved by tuning the incident electron energy and temperature.

Undoped and Mn-doped periodic BST multilayers have been prepared by chemical solution deposition method. Mn2+ tends to substitute for Ti4+ in the BST lattice and introduces more oxygen vacancies, which leads to the reduction of the concentration of electrons and the downward shift of the Fermi level. As a result, improved electrical properties, such as lower frequency dispersion of the dielectric constant, lower dielectric loss and leakage current were found for Mn-doped samples. However, excessive Mn leads to the coexistence of Mn2+ and Mn3+ (or Mn4+), which is believed to degenerate the electrical performance of BST multilayers. 1 mol% Mn-doped BST multilayer exhibits the best electrical performance, with leakage current density of 2.1 × 10−5 A/cm2 (at 100 kV/cm), dielectric loss of ∼0.08 (at 10 kHz) and the minimum frequency dispersion of the dielectric constant.

The light harvesting properties have been numerically investigated in c-silicon/a-silicon core-shell nanopillar array. The influence of shell thickness on optical absorption versus different core diameter has been thoroughly analyzed by using finite-difference time-domain (FDTD) simulations. It is found that a-silicon shell significantly enhanced infrared absorption especially for smaller diameter nanopillar. As a result, the core-shell nanopillar device exhibits a absorption enhancement from 0.22 to 0.65 at 800nm and from 0.05 to 0.43 at 1000nm. Furthermore, the mechanism of the absorption has been discussed.

Silicon nanowires radial core-shell solar cells have recently attracted significant attention as promising candidates for low cost photovoltaic application, benefit from its strong light trapping, and short radial carrier collection distances. In order to establish optics and electricity improvement, a two-dimensional model based on Shockley-Read-Hall recombination modes has been carried out for radial core-shell junction nanowires solar cell combined with guided resonance modes of light absorption. The impact of SiNWs diameter and absorption layer thickness on device electrical performance based on a fixed nanowires height and diameter-over-periodicity were investigated under illumination. The variation in quantum efficiency indicated that the performance is limited by the mismatch between light absorption and carriers’ collection length.

We propose the perfect all-carbon axisymmetric spintronic devices consisting of a zigzag-edged trigonal graphene (ZTG) linked to left and right zigzag-edged graphene nanoribbons (ZGNR) electrodes via carbon atomic chains (CACs). To ensure the stability of the system, the edge carbon atoms are passivated by hydrogen atoms. The self-consistent density functional theory (DFT) calculations show that the simple all-carbon system possesses the prefect spin-filtering property at a wide voltage region from −1.0 to 1.0 V. More importantly, the proposed system can act as a perfect dual spin diode in the antiparallel (AP) spin configuration, and the single-spin rectifying ratio can reach 103. When we add the number of the CACs linked to the left ZGNR electrode, the device shows the obvious single-spin negative differential resistance (NDR) behavior, which originates from the appearance of the localized states in the region of the left ZGNR electrode and ZTG. Meanwhile, the perfect spin-filtering and dual spin-diode ...

We examine the thermospin properties of an all-carbon nanojunction constructed by a graphene nanoflake (GNF) and zigzag-edged graphene nanoribbons (ZGNRs), bridged by the carbon atomic chains. The first-principles calculations show that the phonon thermal conductance is much weaker than the electron thermal conductance at the Fermi level, and even the former is a few percent of the latter in the low-temperature regime. In the meantime, the carbon-based device possesses an excellent spin transport property at the Fermi level due to the appearance of half-metallic property. Furthermore, the single-spin Seebeck coefficient has a larger value at the Fermi level. These facts ultimately result in a significant enhancement of spin thermoelectric figure of merit (FOM) ZST. By controlling the carbon-chain lengths and the temperature, the maximal value of ZST can reach 30. Moreover, we also find that the room temperature ZST displays an odd-even effect with the carbon-chain lengths, and it is always larger than the charge thermoelectric FOM ZCT.

In this work, in order to enhance the light absorption in one micron thick crystalline silicon solar cells, a back reflecting and rear located plasmonic nanodisk scheme is proposed. We investigate the scattering properties of aluminum nanostructures located at the back side and optimize them for enhancing absorption in the silicon layer by using finite difference time domain simulations. The results indicate that the period and diameters of nanodisks, thickness of spacer layer have a strong impact on short circuit current enhancements. The optimized Al nanoparticle arrays embedded in rear located SiO2 layer enhance J sc with an increase of 47% from the non-plasmonic case of 18.9 to 27.8 mA/cm2 when comparing with a typical stack with a planar aluminum back reflector and a back reflector with plasmonic nanoparticles. This finding could lead to improved light trapping within a thin silicon solar cell device.

Graphene planar silicon heterojunction solar cells were investigated using 2D physics-based TCAD simulation. A planar structure consisting of graphene layer as the hole transport material, and n-type silicon as substrate is simulated. Process modeling has been carried out especially for highly boron diffusion. Using this model, the effect of the highly doped surface inverse region located as 0.08, 0.22, 0.35 μm on the photovoltaic performance has been studied. The obtained J–V characteristic is analyzed to study effects of the inverse region depth and doping concentration on Schottky junction modification. The proposed design proves to be highly efficient in 0.2 h annealing, which provides a new platform to further enhance the performance of graphene planar solar cell.

Fourier ptychographic microscopy (FPM) is a newly reported techniques that bypasses the SBP barrier of conventional microscope platforms, which gets high-resolution (HR) images with large FOV. FPM uses an LED matrix as the illuminating source of the microscope. Each lighted LED corresponds to a low-resolution (LR) image. An HR image is generated from a set of LR images by FPM. Larger illuminating angle provides higher frequency information for the HR image. Therefore, FPM increases the NA of the low-NA objective lens while maintaining the large FOV. However, the process of FPM is usually time-consuming, since typically hundreds of LR images are recorded and equally involved in the iteration to maintain the quality of reconstruction. In this paper, we proposed a method to accelerate FPM reconstructing process, called Adaptive-FPM. Inspired by the concept of “keyhole imaging” in MRI, we set an energy change threshold in the reconstruction for each LR image to decide whether the image can be skipped in current iteration or not. In this way, some images will be skipped in further iteration, and the total reconstruction time can be reduced. The method was tested by both simulated data and biomedical data, which showed that the new method led to similar results with the original FPM method, while the run-time was reduced a lot.

A planar structure consisting of graphene layer as the hole transport material, and n-type silicon as substrate is simulated. The degradation of this cell caused by high interface state density has been carried out. The simulated results match published experimental results indicating the accuracy of the physics-based model. Using this model, the effect of interface state density as zero, 1×1016cm-2, 1×1017cm-2 on the photovoltaic performance has been studied. The obtained IV and EQE characteristic based on realistic parameters shows that the interface state playing a prominent role in graphene silicon schottky contact.

Fano effect is an important quantum phenomenon in mesoscopic systems, which arises from an interference between the localized state and the extended state. Here we observe an obvious Fano effect near the Fermi level in an all-carbon molecular device consisting of an acene molecule sandwiched between two zigzag graphene nanoribbon (ZGNR) electrodes. By increasing the length of the molecule, an extended state gradually evolves into a localized state. With the aid of the nearby extended state, a Fano effect is achieved. Using a gate voltage, we can easily tune the Fano effect induced by the single-transmission channel. When the spin degree of freedom is involved, the all-carbon device can show a half-metallic property with positive or negative 100% spin polarization at the Fermi level under the gate voltage; meanwhile the spin thermoelectric effect can also be enhanced.

Two dimensional model of graphene silicon heterojunction solar cell with an boron doped surface layer is structured using Silvaco TCAD tools by accurate control of diffusion process. The introduction of inverse doped layer obviously improved the efficiency of heterojunction photovoltaic cell.

In this work, in order to enhance the light absorption in one micron thick crystalline silicon solar cells, a back reflecting and plasmonic nanodisk scheme is proposed. We investigate the scattering properties of aluminum nanostructures located at the back side and optimize them for enhancing absorption in the silicon layer by using finite difference time domain simulations. The results indicate that the period and diameters nanoparticles, spacer layer have a strong impact on short circuit current enhancements. This finding could lead to improved light trapping within a thin silicon solar cell device.

The noise behaviors of the epitaxial Si:P BIB detectors have been investigated by experimental and theoretical tools. The device structure and testing system are presented in detail. The relationship between the noise spectral density and device temperature is analyzed. It is demonstrated that not only thermal noise but also shot noise are strongly dependent on the device temperature.

Design of ion implantation scheme for the planar GaAs blocked-impurity-band (BIB) detectors is performed by numerical simulation. The device structure and the preparation process are presented. It is demonstrated that the implanted Si ion concentration of the absorbing region and the contact region are 5×1015 cm−3 and 4×1019 cm−3, respectively, and can be implemented by four-step implantation with different ion energies and doses.

The performance of graphene based Schottky junction solar cell on silicon substrate is studied theoretically by TCAD Silvaco tools. We calculate the current-voltage curves and internal quantum efficiency of this device at different conditions using tow dimensional model. The results show that the power conversion efficiency of Schottky solar cell dependents on the work function of graphene and the physical properties of silicon such as thickness and doping concentration. At higher concentration of 1e17cm-3 for n-type silicon, the dark current got a sharp rise compared with lower doping concentration which implies a convert of electron emission mechanism. The biggest fill factor got at higher phos doping predicts a new direction for higher performance graphene Schottky solar cell design.

Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work.

We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

— The exo-electron currents from a ACPDP test panel with or without MgO crystals sprayed on MgO film were measured directly after eliminating of the wall-voltage effect. An inverse relationship was established between the statistical delay time and exo-electron currentfrom the MgO cathode film. The spraying of MgO crystals on MgO thin film was observed to reduce the statistical delay time dramatically even for the same exo-electron currents measured. The shift of the inverse curve may be attributed to an increased discharge success probability by the MgO crystals sprayed.

In this study, we attempted to understand the temperature dependence of statistical delay of ac-PDPs. Two theoretical models, Auger mechanism of thermal excitation and Tunneling model, were used to predict the temperature and time dependency of exo-electron currents. In the Auger mechanism model, a distributed source of trapped electrons was used. The theoretical prediction from the Auger model showed a significant discrepancy from the experimentally measured results from the panels with MgO nano-cube powder coating. The tunneling model seems to describe the exo-electron currents from MgO nano-cube powders better.

The relationship between IR and VUV emission was investigated in an opposed PDP discharge at high Xe content and high voltage levels. The ratio of VIS/IR and the ratio of Efficacy/VIS/IR were determined to analyze the behavior of the xenon excitation efficiency and the electron excitation efficiency as a function of driving voltage and xenon content. We see that the xenon excitation efficiency is almost independent from the driving voltage, and is increasing approximately linearly with the xenon partial pressure.

The effect of the MgO crystal structure on the addressing discharge jitter in SMPDP is investigated. By varying the oxygen pressure during E-beam deposition, different MgO crystal structure was made, as analyzed by XRD. The jitter time in a PDP panel was measured for isolated On-pixels at low intensity levels. The conclusion is that the jitter time can be decreased by maximizing the relative (200)/(111) peak ratio, obtained by decreasing the O2 addition during E-Beam MgO deposition.

Photoluminescence (PL) spectra were recorded for doped MgO crystals, irradiated by VUV light (λ=147nm, hv=8.4eV) in vacuum at room temperature. The emission band between 200 nm and 800nm was observed. Two strong emission peaks are found, one around 330nm and one centered at about 700nm. We assume that the 330nm peak is a recombination emission peak, while the 700nm peak is supposed to be related to hole traps. The crystals were then baked in air for 1h at 150°C, 450°C and 800°C, after which the samples were studied with PL analysis. The trend is that the recombination peak around 330nm increases with baking temperature, suggesting that the heat-cleaning treatment improves the recombination emission characteristics of doped MgO crystals.

A comparative study of photoluminescence and thermoluminescence for both pure and doped MgO poly-crystals has been performed. for pure MgO, a red emission band at 730nm can be observed under VUV light excitation. The doped MgO exhibits a strong emission at 650 nm excited by the VUV or 250 nm light. After exposure to VUV radiation, a strong TL peak corresponding to red emission band can be detected in the temperature range of 20°C–250°C for both doped and undoped MgO. Using Hoogenstraaten's heating rate method, a trap depth of 0.31 eV can be obtained for pure MgO. The trap depth in doped MgO is about 0.51 eV and shifts to high energy level due to the addition of the doping element.

The influence of sustaining frequency on the discharge of Shadow Mask PDP (SM-PDP) is been investigated by both experiments and two dimensional simulations. The ratio of VIS/IR and Efficacy/(VIS/IR) is used to illustrate the xenon excitation efficiency and electron heating efficiency respectively. It can be seen from the simulations that the decrease of efficacy in high sustaining frequency is the result of long life xenon metastables relative to the repetition rate, cannot convert into xenon excimer efficiently and therefore a lower value of the overall discharge efficiency.