No abstract

It was expected that the properties of intrinsic point defects would be simple in the binary semiconductor Sb2Se3. However, we show using first-principles calculations that the intrinsic defects in this quasi-one-dimensional (Q1D) semiconductor are unexpectedly complicated and different from those in conventional photovoltaic semiconductors such as CdTe or GaAs. First, the same type of defects located on non-equivalent atomic sites can have very different properties due to the low symmetry of the Q1D structure, which makes the properties of point defects complicated, even though there are only a few point defects. Second, uncommon defects such as the cation-replace-anion antisite SbSe, anion-replace-cation antisite SeSb, and even two-anion-replace-one-cation antisite 2SeSb, which are difficult to form in CdTe and GaAs, can have high concentrations and even be dominant in Sb2Se3 due to the weak van der Waals interactions and the large void space between different [Sb4Se6] n atomic chains of the Q1D structure. These defects produce a series of acceptor and donor levels in the band gap and make Sb2Se3 p-type under the Se-rich condition but n-type under the Se-poor condition. Five deep-level recombination-center defects are identified, and their formation is difficult to suppress, imposing a serious limit to the development of high-efficiency Sb2Se3 solar cells. Our study demonstrates that the defects can be complicated and unconventional in the binary compound semiconductors with low symmetry and Q1D structures, which can be classified as chemically binary while structurally multinary.

Lithium–sulfur batteries (LSBs) with a high theoretical capacity of 1675 mAh g−1 hold promise in the realm of high‐energy‐density Li–metal batteries. To cope with the shuttle effect and sluggish transformation of soluble lithium polysulfides (LiPSs), varieties of traditional metal‐based materials (such as metal, metal oxides, metal sulfides, metal nitrides, and metal carbides) with unique catalytic activity for accelerating LiPSs redox have been exploited to fundamentally inhibit the shuttle effect and improve the performance of LSBs. Concurrently, some budding catalytic materials also possess enormous potential for facilitating LiPSs redox reaction in LSBs, including metal borides, metal phosphides, metal selenides, single atoms, and defect‐engineered materials. Here, recent advances in these emerging catalytic candidates as well as the evaluation methods and parameters for catalytic materials are comprehensively summarized for the first time. New insights are also given to aid in the design of high‐performance LSBs and satisfy the high expectation in the future, including the exposure of the active sites and adsorption‐catalysis synergy strategies. Finally, the current challenges and prospects for designing highly efficient catalytic materials are highlighted, aiming at providing guidance for configuring catalytic materials to make sure high‐energy and long‐life LSBs.

Co–Zn/N–C polyhedral nanocages: porous bimetallic Co/Zn embedded N-doped carbon (Co–Zn/N–C) polyhedral nanocages have been synthesized through annealing a ZIF-8@ZIF-67 precursor for the first time. The excellent lithium-storage ability is attributed to the unique structure of Co–Zn/N–C.

used as a cathode material. However, there are many shortcomings to hinder the development of Li-S batteries. First, insulating nature of sulfur and its discharge products (Li 2 S) lead to the poor electrochemical activity and low utilization of sulfur. On the other hand, during the charge/discharge process, the long-chain lithium polysulfides (Li 2 S x , 4 ≤ x ≤ 8) are very easily dissolved in the organic electrolyte [4,5] and diffuse toward the anode conductive bone, which results in undesired shuttle reactions, a rapid fading of capacity and lower Coulombic efficiency. [6] In order to promote the development of Li-S batteries, many researchers have tried attempts to solve these problems. For example, a variety of carbon materials have been designed as the host of sulfur with good electrical conductivity such as graphite or graphene, [7][8][9][10] meso-/ microporous carbon, [11,12] carbon nanotubes (CNTs)/nanofibers, [13][14][15] hollow carbon nanospheres, [16,17] and so on. Furthermore, porous carbon materials could effectively alleviate the dissolution and shuttle reactions of intermediate polysulfides by physical absorbability of pores. [11] By means of combination with chemical functionality, N-rich porous carbon materials have extensively attracted researchers' attention. For instance, Zhang and co-workers have presented a facile integration of high-quality aligned CNTs and graphene (ACNT/G hybrids) without barrier layers, followed by the process of nitrogen doping (N-ACNT/G hybrids). After combination with sulfur, electrochemical tests fully verify the superior cathode performance of N-ACNT/G hybrids to pristine ACNT/G. [18] According to the documents, pyridinic and pyrrolic nitrogen atoms can well provide abundant active sites and relieve "sulfur shuttling" by strong Li-N chemical interactions with soluble polysulfides. [19,20] Our group has reported dual N/O-doped carbon materials and explored it as carbon hosts. Because of the surficial chemical absorption function of heteroatoms for long-chain polysulfides, the related cells achieve a stable cyclic performance, even though the carbon matrix exhibits a low surface area. [19] More recently, Zheng and co-workers have proposed the derivation from metal-organic frameworks (MOFs), i.e., a synergistic composite containing cobalt and N-doped graphitic carbon (Co-N-GC), which demonstrates doped carbon facilitating S redox process and a remarkable enhancement of performance. [20] As we all known, nitrogen atoms doped in carbon matrix are beneficial for Herein, a flexible method is designed to engineer nitrogen-doped carbon materials (NC) with different functional and structural specialties involving N-doping level, graphitization, and surface area via tuning the carbonization temperature of the pre-prepared zeolitic imidazolate framework-8 (ZIF-8 ) crystals. With the aim to unveil the effect of these features on the electrochemical performance of sulfur cathode, these samples are evaluated as sulfur host and comprehensively investigated. NC-800 (800 °C, 10.45%N...

Recently, layered perovskites attracted great attention for its excellent stability and light-emitting property. However, most of them rely on the toxic element lead and their emission quantum yields are generally low. Here, a unique hollow two-dimensional perovskite was developed in which the organic hexamethylene diamines (CHN) strongly coupled with distorted tin bromide anions (SnBr). This toxic-free low-dimensional tin perovskite exhibits a broadband emission in the visible region with a high luminescence quantum yield of 86%. First-principles calculation indicate the broadband emission is associated with the recombination of self-trapped excitons. And the emission is related to the geometry of tin bromide anions. An ultraviolet light-pumped white light emitting diode with excellent color-rendering index of 94 was fabricated using it together with a commercially available blue phosphor.

Use of catalytic materials is regarded as the most desirable strategy to cope with sluggish kinetics of lithium polysulfides (LiPSs) transformation and severe shuttle effect in lithium-sulfur batteries (LSBs). Single-atom catalysts (SACs) with 100 %a tom-utilization are advantagous in serving as anchoring and electrocatalytic centers for LiPSs.H erein, an ovel kind of tungsten (W) SACi mmobilized on nitrogendoped graphene (W/NG) with au nique W-O 2 N 2 -C coordination configuration and ah igh Wl oading of 8.6 wt %i s proposed by as elf-template and self-reduction strategy.T he local coordination environment of Watom endows the W/NG with elevated LiPSs adsorption ability and catalytic activity. LSBs equipped with W/NG modified separator manifest greatly improved electrochemical performances with high cycling stability over 1000 cycles and ultrahigh rate capability. It indicates high areal capacity of 6.24 mAh cm À2 with robust cycling life at ahigh sulfur mass loading of 8.3 mg cm À2 .

Defect‐rich carbon materials possess high gravimetric potassium storage capability due to the abundance of active sites, but their cyclic stability is limited because of the low reversibility of undesirable defects and the deteriorative conductivity. Herein, in situ defect‐selectivity and order‐in‐disorder synergetic engineering in carbon via a self‐template strategy is reported to boost the K+‐storage capacity, rate capability and cyclic stability simultaneously. The defect‐sites are selectively tuned to realize abundant reversible carbon‐vacancies with the sacrifice of poorly reversible heteroatom‐defects through the persistent gas release during pyrolysis. Meanwhile, nanobubbles generated during the pyrolysis serve as self‐templates to induce the surface atom rearrangement, thus in situ embedding nanographitic networks in the defective domains without serious phase separation, which greatly enhances the intrinsic conductivity. The synergetic structure ensures high concentration of reversible carbon‐vacancies and fast charge‐transfer kinetics simultaneously, leading to high reversible capacity (425 mAh g−1 at 0.05 A g−1), high‐rate (237.4 mAh g−1 at 1 A g−1), and superior cyclic stability (90.4% capacity retention from cycle 10 to 400 at 0.1 A g−1). This work provides a rational and facile strategy to realize the tradeoff between defect‐sites and intrinsic conductivity, and gives deep insights into the mechanism of reversible potassium storage.