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Over 11% Efficient Eco-Friendly Kesterite Solar Cell: Effects of S-Enriched Surface of Cu2ZnSn(S,Se)4 Absorber and Band Gap Controlled (Zn,Sn)O Buffer
For high efficiency kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cell, CdS thin film was usually used as a buffer layer. However, due to the toxicity of Cd and pollution problems involved from the solution-based chemical bath deposition, eco-friendly high efficiency CZTSSe solar cell with Cd-free buffer is necessary. As an Cd-free buffer layer, we investigated (Zn,Sn)O (ZTO) film deposited by sputtering method. In order to achieve high power conversion efficiency, we controlled energy band gaps of CZTSSe absorber as well as ZTO buffer, which was required to optimize conduction band offset (CBO) between the absorber and the buffer and to increase open circuit voltage (Voc) and fill factor (FF). The CBO was optimized by controlling the band gap of ZTO. By varying the Sn/(Zn + Sn) ratio and its deposition temperature, band gap of ZTO was successfully adjusted. Experimental and computational calculation results showed that solar cell performance was strongly affected by the CBO between absorber and buffer. Besides CBO matching, larger band gap of ZTO improved short circuit current density (Jsc) with enhanced external quantum efficiency value in blue photon spectrum range. As an additional way to improve power conversion efficiency of solar cell, band graded CZTSSe absorber was developed by using spray-based two-step process. The sprayed CZTSSe film was engineered to have S-enriched surface, which makes surface band gap widened and surface passivated, and resultantly increases Voc, Jsc and fill factor (FF). By controlling band gaps of both CZTSSe absorber and ZTO buffer, we obtained 11.22% environment-friendly CZTSSe solar cell without MgF2 anti-reflection coating.
Opposite current-induced spin polarizations in bulk-metallic Bi 2 Se 3 and bulk-insulating Bi 2 Te 2 Se topological insulator thin flakes
One of the most fundamental and exotic properties of three-dimensional (3D) topological insulators (TIs) is spin-momentum locking (SML) of their topological surface states (TSSs), promising for potential applications in future spintronics. However, other possible conduction channels, such as a trivial two-dimensional electron gas (2DEG) with strong Rashba-type spin-orbit interaction (SOI) and bulk-conducting states that may possess a spin Hall effect (SHE), can coexist in 3D TIs, making determining the origin of the current-induced spin polarization (CISP) difficult. Here, we directly compared the CISP between bulk-insulating Bi 2 Te 2 Se (BTS221) and bulk-metallic Bi2Se3 thin flakes using spin potentiometry. In the bulk-insulating BTS221, the observed CISP has a sign consistent with the expected helicity of the SML of the TSS, but an opposite sign to its calculated bulk spin Hall conductivity. However, compared to BTS221, an opposite CISP is observed in the bulk-metallic Bi2Se3, consistent with both the expectations of its Rashba-Edelstein effect of the band-bending induced 2DEG and bulk intrinsic spin Hall Effect (SHE). If one assumes a representative occupation of the Rashba band of 3×10 13 cm –2 in Bi 2 Se 3 with a relevant relaxation time of 100 fs, the contribution to the CISP could be more dominated by the bulk intrinsic SHE. Our results provide an electrical way to distinguish the TSS from other possible conducting channels in spin transport measurements on 3D TIs, and open ways for the potential applications in charge-spin conversion devices.
Gamma decay of Se super 73m, g and Se super 81m, g isomeric pairs.
Gamma decay of Se 73 and Se 81 isomeric pairs with half-lives, energies and decay schemes
Air-Stable Monolayer Cu 2 Se Exhibits a Purely Thermal Structural Phase Transition
Not provided.
A Surface Se-Substituted LiCo[O 2-δ Se δ ] Cathode with Ultrastable High-Voltage Cycling in Pouch Full-Cells
Cycling LiCoO 2 to above 4.5 V for higher capacity is enticing; however, hybrid O anion- and Co cation-redox (HACR) at high voltages facilitates intrinsic O α - (α < 2) migration, causing oxygen loss, phase collapse, and electrolyte decomposition that severely degrade the battery cyclability. Hereby, commercial LiCoO 2 particles are operando treated with selenium, a well-known anti-aging element to capture oxygen-radicals in the human body, showing an “anti-aging” effect in high-voltage battery cycling and successfully stopping the escape of oxygen from LiCoO 2 even when the cathode is cycled to 4.62 V. Furthermore, ab initio calculation and soft X-ray absorption spectroscopy analysis suggest that during deep charging, the precoated Se will initially substitute some mobile O α - at the charged LiCoO 2 surface, transplanting the pumped charges from O α - and reducing it back to O 2- to stabilize the oxygen lattice in prolonged cycling. As a result, the material retains 80% and 77% of its capacity after 450 and 550 cycles under 100 mA g -1 in 4.57 V pouch full-cells matched with a graphite anode and an ultralean electrolyte (2 g Ah -1 ).
Octahedral to tetrahedral bonding transitions in the local structure of phase change optical media Ge 2 Sb 2 Se 5 x Te 5-5 x with Se doping
Random access memories utilize fast, reversible switching between ordered and disordered states of matter in phase change materials (PCMs) such as Ge2Sb2Te5-5x. The short-range structure in the disordered phase has been described either as (i) a network of Ge tetrahedra or (ii) Peierls distorted Ge/Sb octahedra. The PCM transition was investigated in bulk Ge2Sb2Se5xTe5-5x (GSST), in which amorphization sets in with Se doping (x ≈ 0.85) upon quenching. GSST has a hexagonal crystalline ground state with Ge/Sb octahedral coordination, but the phase change transition to the amorphous state that is only observed when the system is quenched brings a short-range structure with sharp, tetrahedrally coordinated Ge/Sb correlations and shortened bonds that are distinctly different from the expected octahedral pairing.
The chalcogenide semiconductor system - As sub 2 Se sub 3-Sb sub 2 Se sub 3.
Glass formation region of chalcogenide semiconductor arsenic triselenide-antimony triselenide system and vitreous-crystalline transformation, investigating electrical and optical properties
Materials Data on Se by Materials Project
Se is alpha-like structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four cyclooctaselenium molecules. there are eight inequivalent Se sites. In the first Se site, Se is bonded in a water-like geometry to two Se atoms. Both Se–Se bond lengths are 2.36 Å. In the second Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the third Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the fourth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the fifth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the sixth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the seventh Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the eighth Se site, Se is bonded in a water-like geometry to two Se atoms.
Materials Data on Se by Materials Project
Se is beta Selenium structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four cyclooctaselenium molecules. there are eight inequivalent Se sites. In the first Se site, Se is bonded in a water-like geometry to two Se atoms. Both Se–Se bond lengths are 2.36 Å. In the second Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the third Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the fourth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the fifth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the sixth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the seventh Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the eighth Se site, Se is bonded in a water-like geometry to two Se atoms.
Materials Data on Se by Materials Project
Se is red selenium structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight cyclooctaselenium molecules. there are eight inequivalent Se sites. In the first Se site, Se is bonded in a water-like geometry to two Se atoms. Both Se–Se bond lengths are 2.36 Å. In the second Se site, Se is bonded in a water-like geometry to two Se atoms. Both Se–Se bond lengths are 2.37 Å. In the third Se site, Se is bonded in a water-like geometry to two Se atoms. There are one shorter (2.36 Å) and one longer (2.37 Å) Se–Se bond lengths. In the fourth Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.37 Å. In the fifth Se site, Se is bonded in a water-like geometry to two Se atoms. In the sixth Se site, Se is bonded in a water-like geometry to two Se atoms. In the seventh Se site, Se is bonded in a water-like geometry to two Se atoms. The Se–Se bond length is 2.36 Å. In the eighth Se site, Se is bonded in a water-like geometry to two Se atoms.
SE-FIT
The mathematical theory of capillary surfaces has developed steadily over the centuries, but it was not until the last few decades that new technologies have put a more urgent demand on a substantially more qualitative and quantitative understanding of phenomena relating to capillarity in general. So far, the new theory development successfully predicts the behavior of capillary surfaces for special cases. However, an efficient quantitative mathematical prediction of capillary phenomena related to the shape and stability of geometrically complex equilibrium capillary surfaces remains a significant challenge. As one of many numerical tools, the open-source Surface Evolver (SE) algorithm has played an important role over the last two decades. The current effort was undertaken to provide a front-end to enhance the accessibility of SE for the purposes of design and analysis. Like SE, the new code is open-source and will remain under development for the foreseeable future. The ultimate goal of the current Surface Evolver Fluid Interface Tool (SEFIT) development is to build a fully integrated front-end with a set of graphical user interface (GUI) elements. Such a front-end enables the access to functionalities that are developed along with the GUIs to deal with pre-processing, convergence computation operation, and post-processing. In other words, SE-FIT is not just a GUI front-end, but an integrated environment that can perform sophisticated computational tasks, e.g. importing industry standard file formats and employing parameter sweep functions, which are both lacking in SE, and require minimal interaction by the user. These functions are created using a mixture of Visual Basic and the SE script language. These form the foundation for a high-performance front-end that substantially simplifies use without sacrificing the proven capabilities of SE. The real power of SE-FIT lies in its automated pre-processing, pre-defined geometries, convergence computation operation, computational diagnostic tools, and crash-handling capabilities to sustain extensive computations. SE-FIT performance is enabled by its so-called file-layer mechanism. During the early stages of SE-FIT development, it became necessary to modify the original SE code to enable capabilities required for an enhanced and synchronized communication. To this end, a file-layer was created that serves as a command buffer to ensure a continuous and sequential execution of commands sent from the front-end to SE. It also establishes a proper means for handling crashes. The file layer logs input commands and SE output; it also supports user interruption requests, back and forward operation (i.e. undo and redo), and others. It especially enables the batch mode computation of a series of equilibrium surfaces and the searching of critical parameter values in studying the stability of capillary surfaces. In this way, the modified SE significantly extends the capabilities of the original SE.
Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77 Se and 113 Cd Solid-State NMR Spectroscopy
Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113 Cd and 77 Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113 Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe 3 O, CdSe 2 O 2 , and CdSeO 3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113 Cd– 113 Cd and 77 Se– 77 Se and heteronuclear 113 Cd– 77 Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77 Se{ 113 Cd} scalar heteronuclear multiple quantum coherence ( J -HMQC) experiments were used to selectively measure one-bond 77 Se– 113 Cd scalar coupling constants ( 1 J ( 77 Se, 113 Cd)). With knowledge of 1 J ( 77 Se, 113 Cd), heteronuclear 77 Se{ 113 Cd} spin echo ( J -resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. Furthermore, the J -resolved experiments directly confirmed that major Cd and Se surface species have CdSe 2 O 2 and SeCd 4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.