Acceptor alloys based on n‐type small molecular and fullerene derivatives are used to fabricate the ternary solar cell. The highest performance of optimized ternary device is 10.4%, which is the ...highest efficiency for one donor/two acceptors‐based ternary systems. Three important parameters, JSC, VOC, and FF, of the optimized ternary device are all higher than the binary reference devices.
Internal magnetic moments induced by magnetic dopants in MoS2 monolayers are shown to serve as a new means to engineer valley Zeeman splitting (VZS). Specifically, successful synthesis of monolayer ...MoS2 doped with the magnetic element Co is reported, and the magnitude of the valley splitting is engineered by manipulating the dopant concentration. Valley splittings of 3.9, 5.2, and 6.15 meV at 7 T in Co‐doped MoS2 with Co concentrations of 0.8%, 1.7%, and 2.5%, respectively, are achieved as revealed by polarization‐resolved photoluminescence (PL) spectroscopy. Atomic‐resolution electron microscopy studies clearly identify the magnetic sites of Co substitution in the MoS2 lattice, forming two distinct types of configurations, namely isolated single dopants and tridopant clusters. Density functional theory (DFT) and model calculations reveal that the observed enhanced VZS arises from an internal magnetic field induced by the tridopant clusters, which couples to the spin, atomic orbital, and valley magnetic moment of carriers from the conduction and valence bands. The present study demonstrates a new method to control the valley pseudospin via magnetic dopants in layered semiconducting materials, paving the way toward magneto‐optical and spintronic devices.
The synthesis of a Co‐doped MoS2 monolayer with enhanced valley Zeeman splitting is reported. Valley splittings are revealed by polarization‐resolved photoluminescence spectroscopy. Atomic‐resolution electron microscopy studies clearly identify the magnetic sites of Co substitution in the MoS2 lattice. The enhanced valley Zeeman splitting is further demonstrated by density functional theory and model calculations.
The nonlinear Hall effect, which is the second-order harmonic charge Hall effect from the Berry curvature dipole in momentum space, has received much attention recently. As the responses to higher ...harmonics of the driving ac electric field are prominent and measurable, we develop a general nonlinear theory by taking the charge and spin currents as well as the longitudinal and transverse effects into account. We introduce the expansion order of the electric field and Berry curvature multipole moment, where the Berry curvature dipole is a particular one manifesting itself at the second harmonic order and the second expansion order of the electric field. There are four cases with conserving or breaking the time-reversal symmetry (TRS) and inversion symmetry (IS). We find a specific "selection rule" that only longitudinal odd harmonic order charge currents exist for conserving both the TRS and IS, and with breaking both symmetries, all harmonic order charge and spin currents are nonzero. With conserving TRS and breaking IS, the charge Hall current exists at even harmonic order, and the longitudinal charge current occurs at odd harmonic order. Only the longitudinal spin current survives at even harmonic order. With breaking TRS and conserving IS, only odd harmonic order charge and spin currents can appear. Moreover, we observe that every harmonic order current contains a series of infinite-order expansion of the electric field. We further show that the Berry curvature dipole and quadrupole can be determined by measuring the second and fourth harmonic order currents in experiments. This may open a way to explore the higher responses of an ac driving system.
A well-known scheme for generating Majorana zero-energy modes is a heterojunction of s-wave superconductor and topological insulator that induces an equivalent two-dimensional p-wave superconductor ...at the interface. In this work, we construct a cylindrical system based on the heterojunction with the external magnetic field. We investigate the Aharonov–Bhom phase (A–B phase) of Majorana zero-energy state, find that the A–B phase between two Majorana zero-energy states located at the inner and outer boundaries of the ring system will interfere with each other. The intensity of interference fringes may change with A–B phase, which indicates that we can store the quantum information through the A–B phase and construct a single qubit A–B phase gate. We further explore the splitting of zero-bias conductance peak caused by the A–B phase and adjust the splitting energy by the A–B phase.
Graphic Abstract
Organic-inorganic halide perovskite solar cells have enormous potential to impact the existing photovoltaic industry. As realizing a higher conversion efficiency of the solar cell is still the most ...crucial task, a great number of schemes were proposed to minimize the carrier loss by optimizing the electrical properties of the perovskite solar cells. Here, we focus on another significant aspect that is to minimize the light loss by optimizing the light management to gain a high efficiency for perovskite solar cells. In our scheme, the slotted and inverted prism structured SiO2 layers are adopted to trap more light into the solar cells, and a better transparent conducting oxide layer is employed to reduce the parasitic absorption. For such an implementation, the efficiency and the serviceable angle of the perovskite solar cell can be promoted impressively. This proposal would shed new light on developing the high-performance perovskite solar cells.
The spin and valley-dependent anomalous Nernst effects are analyzed for monolayer MoS_{2} and other group-VI dichalcogenides. We find that pure spin and valley currents can be generated perpendicular ...to the applied thermal gradient in the plane of these two-dimensional materials. This effect provides a versatile platform for applications of spin caloritronics. A spin current purity factor is introduced to quantify this effect. When time reversal symmetry is violated, e.g., two-dimensional materials on an insulating magnetic substrate, a dip-peak feature appears for the total Nernst coefficient. For the dip state it is found that carriers with only one spin and from one valley are driven by the temperature gradient.
This article gives an overview on recent theoretical progress in controlling the charge and spin dynamics in low-dimensional electronic systems by means of ultrashort and ultrabroadband ...electromagnetic pulses. A particular focus is put on sub-cycle and single-cycle pulses and their utilization for coherent control. The discussion is mostly limited to cases where the pulse duration is shorter than the characteristic time scales associated with the involved spectral features of the excitations. The relevant current theoretical knowledge is presented in a coherent, pedagogic manner. We work out that the pulse action amounts in essence to a quantum map between the quantum states of the system at an appropriately chosen time moment during the pulse. The influence of a particular pulse shape on the post-pulse dynamics is reduced to several integral parameters entering the expression for the quantum map. The validity range of this reduction scheme for different strengths of the driving fields is established and discussed for particular nanostructures. Acting with a periodic pulse sequence, it is shown how the system can be steered to and largely maintained in predefined states. The conditions for this nonequilibrium sustainability are worked out by means of geometric phases, which are identified as the appropriate quantities to indicate quasistationarity of periodically driven quantum systems. Demonstrations are presented for the control of the charge, spin, and valley degrees of freedom in nanostructures on picosecond and subpicosecond time scales. The theory is illustrated with several applications to one-dimensional semiconductor quantum wires and superlattices, double quantum dots, semiconductor and graphene quantum rings. In the case of a periodic pulsed driving the influence of the relaxation and decoherence processes is included by utilizing the density matrix approach. The integrated and time-dependent spectra of the light emitted from the driven system deliver information on its spin-dependent dynamics. We review examples of such spectra of photons emitted from pulse-driven nanostructures as well as a possibility to characterize and control the light polarization on an ultrafast time scale. Furthermore, we consider the response of strongly correlated systems to short broadband pulses and show that this case bears a great potential to unveil high order correlations while they build up upon excitations.
Organic–inorganic halide perovskites are quite promising in applications of large scale photovoltaic technology. However, toxicity is one of the crucial issues in these materials, and searching for ...environmentally friendly perovskite materials for green energy applications is in high demand. Here we present a systematic ab initio study on the replacement of toxic Pb in the perovskite CH3NH3PbI3 (MAPbI3) with possible mono- and a few binary replacements. In the mono-replacements study, Ge and Sn are the best alternatives to Pb. In the binary replacements, we replace Pb by mixing Ca/Si and Zn/Si. In case of Ca/Si, a monotonic decrease in band gaps with a monotonic increase in the optical absorption was observed with increasing the Ca concentration. It is observed for the first time that the substitution of Ca/Si (or Zn/Si) at the B-site with various ratios would lead to remarkably high device absorption efficiencies. The band gaps of the studied mixed replacements are in the ideal ranges for single-junction solar cell and one cell in tandem architecture. As a result of the smaller effective masses, the mixed replacements could have better carrier mobility. An ab initio molecular dynamic simulation demonstrates the stability of the mixed replacements. More importantly, the mixed substituting elements are highly abundant in the earth. This work is helpful to gain further insights into developing green solar cells with low cost and high performance and would lead to wide applications in the future.
It remains a challenge to exploit dual-functional metal–organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the ...bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH2bts), and the phosphonic acid ligand N,N′-piperazine (bismethylenephosphonic acid; H4L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, Tb(H2L)(H2bts)(H2O)·H2O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10–4 S cm–1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.
We theoretically analyze the nonlinear anomalous Nernst effect as the second-order response of temperature gradient by using the semiclassical framework of electron dynamics. We find that a nonlinear ...current can be generated transverse to the applied temperature gradient in time-reversal-symmetry materials with broken inversion symmetry. This effect has a quantum origin arising from the Berry curvature of states near the Fermi surface. We discuss the nonlinear Nernst effect in transition metal dichalcogenides (TMDCs) under the application of uniaxial strain. In particular, we predict that under fixed chemical potential in TMDCs, the nonlinear Nernst current exhibits a transition from T−2 temperature dependence in low temperature regime to a linear T dependence in high temperature.
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