Anion Vacancies Research Articles

Multifunctional Molecule Modification toward Efficient Carbon‐Based All‐Inorganic CsPbIBr2 Perovskite Solar Cells

AbstractFavorable stability is a big challenge for the commercialization of perovskite solar cells, and all‐inorganic perovskite semiconductors have attracted much attention due to their excellent performance in this field. In reality, the poor stability is mainly due to the high‐density defects in the perovskite films, which provide a channel for charge nonradiative recombination and ion migration. In this work, a multifunctional aminoguanidine hemisulfate (AG HSUL) is introduced into the CsPbIBr2 perovskite layer to achieve defect passivation. Guanidine cations (GA+) can form strong hydrogen bonds with under‐coordinated halogen ions to stabilize the crystal lattice; the nitrogen atom in the amino group can form a complex with the under‐coordinated lead ion; inorganic acids and ions can not only compensate for halogen anion vacancies, but also combine with lead clusters or capped lead ions to reduce defect density. The synergistic effect of anions and cations can effectively passivate the defects, and an energy conversion efficiency of 10.10% is obtained at the optimal concentration of modification. In addition, carbon electrodes are used instead of metal electrodes, which greatly reduces the cost. The results provide a new idea for the development of efficient all‐inorganic CsPbIBr2 perovskite solar cells.

Sulfur-doped LaNiO3 perovskite oxides with enriched anionic vacancies and manipulated orbital occupancy facilitating oxygen electrode reactions in lithium-oxygen batteries

The rational design of effective bifunctional catalysts with enhanced activity toward oxygen reduction reaction and oxygen evolution reaction is of significance to develop high-performance lithium-oxygen (Li–O2) batteries. Herein, sulfur-doped LaNiO3 nanoparticles are elaborately synthesized, and their catalytic activity toward oxygen redox reactions in Li–O2 batteries is comprehensively studied. As confirmed by the density functional theory calculations and experimental results, the substitution of oxygen atoms by sulfur atoms with lower Pauling electronegativity can enhance the covalent feature of bonds, thus increasing electrical conductivity of catalyst. In addition, abundant oxygen vacancies created after sulfur doping are capable of providing concentrated active sites. Simultaneously, sulfur dopants boost the hybridization between Ni 3d orbital and O 2p orbital and increase the covalency of Ni–O bonds due to the increase of Ni3+ with the near-unity occupancy of the eg orbital, thereby increasing the adsorption strength of oxygen-containing intermediates on the surface. Eventually, lowered reaction energy barriers and accelerated reaction kinetics of oxygen electrode reactions are realized, contributing to the optimized electrochemical performance of Li–O2 battery. The Li–O2 battery based on sulfur-doped LaNiO3 with the optimized S-doping level of 2.89 wt% (marked as S2.89 wt%-LNO) delivers a high specific discharge capacity of 24067 mAh/g, an ultralow overpotential of 0.37 V and extended life of 347 cycles.

What controls electrostatic vs electrochemical response in electrolyte-gated materials? A perspective on critical materials factors

Electrolyte-gate transistors are a powerful platform for control of material properties, spanning semiconducting behavior, insulator-metal transitions, superconductivity, magnetism, optical properties, etc. When applied to magnetic materials, for example, electrolyte-gate devices are promising for magnetoionics, wherein voltage-driven ionic motion enables low-power control of magnetic order and properties. The mechanisms of electrolyte gating with ionic liquids and gels vary from predominantly electrostatic to entirely electrochemical, however, sometimes even in single material families, for reasons that remain unclear. In this Perspective, we compare literature ionic liquid and ion gel gating data on two rather different material classes—perovskite oxides and pyrite-structure sulfides—seeking to understand which material factors dictate the electrostatic vs electrochemical gate response. From these comparisons, we argue that the ambient-temperature anion vacancy diffusion coefficient (not the vacancy formation energy) is a critical factor controlling electrostatic vs electrochemical mechanisms in electrolyte gating of these materials. We, in fact, suggest that the diffusivity of lowest-formation-energy defects may often dictate the electrostatic vs electrochemical response in electrolyte-gated inorganic materials, thereby advancing a concrete hypothesis for further exploration in a broader range of materials.

Capture and recycling of toxic selenite anions by cobalt-based metal-organic-frameworks for electrocatalytic overall water splitting

A nanosheet-like cobalt-based metal-organic-framework (Co-MOF) is employed to uptake SeO32− anions, and the remove capacity of Co-MOF reaches a record of 280.0 mg g−1. After uptake SeO32− by Co-MOF, the recycling defect-rich CoSeO4 (R-CoSeO4) is used as an electrocatalyst for oxygen evolution reaction (OER), which displays an overpotential of 265 mV at 10 mA cm−2 in 1 M KOH. Furthermore, cobalt-cobalt selenide heterojunction nanoparticle (Co-Co0.85Se), a high-performance hydrogen evolution reaction (HER) electrocatalyst (overpotential of 97 mV at 10 mA cm−2 in 1 M KOH) is obtained by one-step calcining of R-CoSeO4. Series experiments and density functional theory calculations confirm the anion vacancy in R-CoSeO4 and heterojunction in Co-Co0.85Se can improve the OER and HER activity, respectively. Finally, two binder-free electrodes (R-CoSeO4/CC and Co-Co0.85Se/CC) are employed as anode and cathode, respectively, to construct a water electrolysis cell, which only needs 1.47 V to achieve 10 mA cm−2 in 1 M KOH.

Engineering Sulfur Vacancies in Spinel-Phase Co3S4 for Effective Electrocatalysis of the Oxygen Evolution Reaction

Restricted by the sluggish kinetics of the oxygen evolution reaction (OER), efficient OER catalysis remains a challenge. Here, a facile strategy was proposed to prepare a hollow dodecahedron constructed by vacancy-rich spinel Co3S4 nanoparticles in a self-generated H2S atmosphere of thiourea. The morphology, composition, and electronic structure, especially the sulfur vacancy, of the cobalt sulfides can be regulated by the dose of thiourea. Benefitting from the H2S atmosphere, the anion exchange process and vacancy introduction can be accomplished simultaneously. The resulting catalyst exhibits excellent catalytic activity for the OER with a low overpotential of 270 mV to reach a current density of 10 mA cm–2 and a small Tafel slope of 59 mV dec–1. Combined with various characterizations and electrochemical tests, the as-proposed defect engineering method could delocalize cobalt neighboring electrons and expose more Co2+ sites in spinel Co3S4, which lowers the charge transfer resistance and facilitates the formation of Co3+ active sites during the preactivation process. This work paves a new way for the rational design of vacancy-enriched transition metal-based catalysts toward an efficient OER.

Anion‐Doping‐Induced Vacancy Engineering of Cobalt Sulfoselenide for Boosting Electromagnetic Wave Absorption

AbstractVacancy engineering is an attractive approach to modulate the electronic structure of transition metal chalcogens. However, illustrating how anion vacancy can be engineered to tailor their electromagnetic (EM) parameters and electromagnetic wave (EMW) absorption, based on clear vacancy concentrations and/or various anion vacancies rather than semiempirical rules, is currently lacking but significantly desired. An anion‐doping‐induced vacancy engineering is pioneered, where the selective oxidation process upgrades the transformation from Co‐based precursor to S‐doped CoSe2 (System II) instead of Se‐doped CoS2 (System I) in the subsequent sulfuration/selenization, which results in vacancy level improvement and coexistence of sulfur vacancies (VS) and selenium vacancy (VSe). Thanks to the boosted dielectric polarization loss provided by the comparable coexistence of sulfur/selenium vacancies (VS/VSe = 0.52), S‐doped CoSe2 harvests a broad bandwidth of 9.25 GHz (8.75–18.00 GHz) at 2.42 mm. This feature almost simultaneously achieves 100% coverage for X‐, and Ku‐bands, outperforming all reported metal sulfides/selenides until now. This work establishes a clear correlation between vacancy concentrations/various anion vacancies and EMW dissipation ability, offering valuable insights for designing advanced EMW absorbing materials.

Strategies and Methods of Modulating Nitrogen-Incorporated Oxide Photocatalysts for Promoted Water Splitting

ConspectusThe conversion of solar energy to chemicals and the storage of this energy is one of the most promising routes to realizing a “carbon zero” society, for which particulate photocatalytic water splitting to produce hydrogen has been considered to be a clean potential route. For this purpose, many d0 and d10 metal-based nitrogen-incorporated oxide (including nitrogen-doped oxide and oxynitride) semiconductor photocatalysts have been developed as good candidates to harvest major visible regions of solar light and to exhibit suitable energy levels to drive water splitting. Compared to the oxide-type photocatalysts, valence bands of the nitrogen-incorporated oxide can be upshifted in consideration of the lower electronegativity of nitrogen atoms concerning the oxygen atoms.However, a high-temperature nitridation process was needed to introduce nitrogen atoms into the metal oxide lattice. Because of the poor charge balance of the N3– substitution for O2– and the strong reducing effect of the active nitrogen species at high temperature, the nitriding process tends to introduce both anionic vacancy defects as well as low-valent metal ion defects. In addition, the crystal size of (oxy)nitrides synthesized through high-temperature nitridation is generally large, and there is a lack of an effective charge-separation driving force within the bulk of the (oxy)nitrides. Because of the scarcity of surface catalytic sites, the photocatalytic activity of the (oxy)nitrides is rather low.Recently, our group has been devoted to addressing the above key challenges, especially for the d0-metal-based (oxy)nitrides. The new preparation routes and/or methods were carried out to enhance the nitration kinetics for the synthesis of (oxy)nitrides with low-defect concentrations and further fabricate some novel metal (oxy)nitrides. The doping strategies were developed to suppress the generation of low-valent metal ion defects. A one-pot nitridation strategy was developed to construct the type II heterostructures of two metal oxynitrides to enhance their charge separation, and a strategy for the surface modification of metal oxynitrides with inert metal oxides was developed to promote the surface hydrophilicity and the cocatalyst dispersion. In addition, an intimate and strengthened interface between the cocatalyst and the metal oxynitride photocatalyst was achieved by a sequential cocatalyst decoration method, and it was demonstrated that the strengthened interface is beneficial to enhancing the surface charge separation efficiency. Benefitting from these methods and strategies, some novel visible-light-responsive materials have been exploited for promising water splitting, and remarkably improved water splitting performances have been achieved on some typical d0-metal-based (oxy)nitrides regardless of H2/O2-evolving half-reactions and Z-scheme overall water splitting (Z-OWS) reactions. In this Account, we will give a concise summary of these methods and strategies, and the prospects of nitrogen-incorporated oxide photocatalysts for potential water splitting will be examined.

Synthesis, structure, and electrical conductivity of Sr2LiH2N nitride hydride

K2NiF4-type structures, which exhibit diverse anion arrangements, are a promising framework for hydride ion conductors. Here, we synthesized Sr2LiH2N (SLHN), a nitride hydride with K2NiF4-type structure, and investigated the relationship between its structure and hydride ion conductivity. A solid-state reaction at 650 ​°C in a hydrogen atmosphere yielded almost-single-phase tetragonal SLHN. Rietveld analysis revealed that hydride ions occupied the equatorial sites and the apical sites in the perovskite layer whereas the nitride ions preferentially occupied the apical sites. In addition, a substantial amount of the anion vacancies (∼21%) was observed at the apical sites. The electrical conductivity of Sr2LiH2N was 1.1 ​× ​10−6 ​S ​cm−1 ​at 300 ​°C. The solid solutions of Sr2LiH2+xOxN1–x in which nitride ions were partially substituted by oxide and hydride ions were synthesized. The electrical conductivity of Sr2LiH2+xOxN1–x enhanced with increasing oxygen and hydrogen contents and reached the maximum value of 7.2 ​× ​10−6 ​S ​cm−1 for x ​= ​0.2.

Effect of anion and cation vacancies pairs in conduct of the [formula omitted] and [formula omitted] (x = 0.0033) as a memristor

As a memristor with a memory effect, barium titanate (BT) is an excellent choice for designing a memory circuit. Vacancies control the memory effect, performance, and operating temperature of the BT memristor. However, different anion and cation vacancies pairs as Schottky type defects have diverse effects on memristor conducts. In this research, the influence of oxygen and barium vacancies in Ba1−3xTiO31−x as well as oxygen and titanium vacancies in BaTi(1−3x2)O3(1−x) (x = 0.0033) on memristor manner have been investigated by molecular dynamics (MD) simulation. The obtained results indicate the type of pairs vacancies dramatically influence the diffusion of ions, response to DC voltage, and hysteresis loop area. The barium vacancies trapped fewer oxygen vacancies than titanium vacancies. So, Ba1−3xTiO31−x has more oxygen diffusion ions, better electrical current, and more hysteresis loop area than BaTi(1−3x2)O3(1−x). Therefore, Ba1−3xTiO31−x is an appropriate choice for memristor. Memristor manufacturing companies can use the obtained result from this paper to design memristors with more efficiency and low operation temperature.

Boosting the potassium-ion storage performance enabled by engineering of hierarchical MoSSe nanosheets modified with carbon on porous carbon sphere

Developing suitable electrode materials capable of tolerating severe structural deformation and overcoming sluggish reaction kinetics resulting from the large radius of potassium ion (K+) insertion is critical for practical applications of potassium-ion batteries (PIBs). Herein, a superior anode material featuring an intriguing hierarchical structure where assembled MoSSe nanosheets are tightly anchored on a highly porous micron-sized carbon sphere and encapsulated within a thin carbon layer (denoted as Cs@MoSSe@C) is reported, which can significantly boost the performance of PIBs. The assembled MoSSe nanosheets with expanded interlayer spacing and rich anion vacancy can facilitate the intercalation/deintercalation of K+ and guarantee abundant active sites together with a low K+ diffusion barrier. Meanwhile, the thin carbon protective layer and the highly porous carbon sphere matrix can alleviate the volume expansion and enhance the charge transport within the composite. Under these merits, the as-prepared Cs@MoSSe@C anode exhibits a high reversible capacity (431.8 mAh g−1 at 0.05 A g−1), good rate capability (161 mAh g−1 at 5 A g−1), and superior cyclic performance (70.5% capacity retention after 600 cycles at 1 A g−1), outperforming most existing Mo-based S/Se anodes. The underlying mechanisms and origins of superior performance are elucidated by a set of correlated in-situ/ex-situ characterizations and theoretical calculations. Further, a PIB full cell based on Cs@MoSSe@C anode also exhibits an impressive electrochemical performance. This work provides some insights into developing high-performance PIBs anodes with transition-metal chalcogenides.

Reversing the Nucleophilicity of Active Sites in CoP2 Enables Exceptional Hydrogen Evolution Catalysis.

Precisely constructing the local configurations of active sites to achieve on-demand catalytic functions is highly critical yet challenging. Herein, an anion-deficient strategy to precisely capture Ru single atoms on the anion vacancies of CoP2 (Ru-SA/Pv-CoP2 ) is developed. Refined structural characterizations reveal that the Ru single atoms preferably bind to the anion vacancy sites and consequently build a superior catalytic surface with neighboring CoP and CoRu coordination states for the hydrogen evolution reaction (HER) catalysis. The prepared Ru-SA/Pv-CoP2 nanowires exhibit an unprecedented overpotential of 17mV at 10mA cm-2geo , and the corresponding mass activity is 52.2 times higher than the benchmark Pt/C catalyst at the overpotential of 50mV. Theoretical analysis illustrates that the introduced Ru-SAs can reverse electrons state distribution (from nucleophilic P sites to electrophilic Ru sites) and boost the activation of water molecules and hydrogen production. More importantly, such a construction strategy is also applicable for Pt single atom coupling, suggesting its generality in building catalytic sites. The capability to precisely construct active sites offers a powerful platform to manipulate the catalytic performance of HER catalysts and beyond.

Elucidation of the redox activity of Ca2MnO3.5 and CaV2O4 in calcium batteries using operando XRD: charge compensation mechanism and reversibility

Ca2MnO3.5 and CaV2O4 were found to be potentially interesting as positive electrode materials for calcium metal-based high-energy density batteries with DFT-predicted average voltages of 3.7 V and 2.5 V and energy barriers for Ca migration of 1.1 eV and 0.6 eV, respectively. Both compounds were prepared by solid state reaction under reducing atmospheres. Optimum conditions to achieve Ca2MnO3.5 comprised the reduction of Ca2MnO4 under NH3 gas at 420⁰C with a flow rate of 1200 ml/min while CaV2O4 was achieved by reduction of CaV2O6 at 700 ⁰C under H2 flow. Electrochemical oxidation of Ca2MnO3.5 in lithium or calcium cells resulted in the formation of an orthorhombic phase with cell parameter (a= 5.2891(1), b= 10.551(2), c= 12.1422(1)). Operando synchrotron radiation diffraction experiments indicate that the charge compensation mechanism is not related to Ca2+ extraction but to intercalation of F− (originated from electrolyte salt decomposition) into the anion vacancy position, as confirmed by EELS and EDS. This process was found to be irreversible. In the case of CaV2O4, oxidation induces the electrochemical extraction of calcium with the formation of an orthorhombic phase (space group Pbnm) with cell parameters a = 10.72008(9) Å, b = 9.20213(2) Å and c = 2.89418(3) Å. The process was also investigated via operando synchrotron radiation diffraction, with the oxidized phase being found to reintercalate Ca2+ ions upon reduction, with the formation of a solid solution. Preliminary cycling tests reveals a decrease in the polarization after the first cycle and call for further investigation of this system.

Epitaxial TiCx(001) layers: Phase formation and physical properties vs C-to-Ti ratio

Titanium carbide films are deposited onto MgO(001) by reactive magnetron sputtering in Ar/CH4 mixtures at 1100 °C with a varying CH4 fraction fCH4 = 0.4–8%, yielding C-to-Ti ratios x = 0.08–1.8. The microstructure is dominated by an epitaxial rock-salt structure TiCx(001) matrix which contains secondary hcp Ti and graphitic/a-C:H for x ≤ 0.24 and x ≥ 1.5, respectively. First-principles calculations indicate negligible interstitial C in the cubic phase, a large equilibrium phase-field x = 0.5–1 for the cubic structure which is extended to x < 0.5 by entropic stabilization, and a predicted C-solubility in hcp Ti of x = 0.06 at 1100 °C. The measured relaxed lattice constant increases from ao = 0.4304 nm for TiC0.5 to 0.4325 nm for TiC1.0, in excellent agreement with predictions. However, dao/dx for x < 0.5 and x > 1.0 is much smaller than predicted for C vacancies and interstitials in rock-salt TiCx, respectively, confirming secondary phase formation and indicating a minimum x = 0.46 in the cubic phase. The hardness and elastic modulus of phase-pure TiCx(001) increases from H = 24 GPa and E = 304 GPa for TiC0.5 to H = 31 GPa and E = 462 GPa for TiC1.0, which is attributed to an increasing bonding ionicity. H and E decrease with x < 0.5 and x > 1.0 due to secondary phase softening which is well described by an effective medium with homogenous stress. The electrical resistivities for TiC0.5 and TiC1.0 are 168 and 83 μΩ cm at 298 K, and 158 and 72 μΩ cm at 77 K, indicating electron scattering at random anion vacancies for x = 0.5 but also dominant defect scattering for stoichiometric TiC1.0.

Competing Superior Electronic Structure and Complex Defect Chemistry in Quasi-One-Dimensional Antimony Chalcogenide Photovoltaic Absorbers

Antimony chalcogenides Sb2Se3 and Sb2S3 are an emerging class of quasi-one-dimensional van der Waals bonded materials with rapid progress and great promise for low-cost, high-efficiency, and scalable thin-film photovoltaics. Here using first-principles theoretical calculations, we show that antimony chalcogenides Sb2Se3 and Sb2S3 possess competing superior electronic structure and complex defect chemistry, limiting their photovoltaic performance. The high optical absorption, large Born effective charge, and high dielectric constant lead to low exciton binding energy and small hole effective mass, which ultimately benefit the photovoltaic performance. In contrast, quasi-1D antimony chalcogenides exhibit complex defect chemistry. The cation–anion antisites are the dominating native defects in the Sb rich condition, while in the Sb poor condition the anion–cation antisites are dominant. In both cases, the anion vacancies are also easy to form. These native defects introduce midgap transition levels which act as electron–hole recombination centers, limit the dopability, and lower the open circuit voltage. As a result, Sb2Se3 is a p-type semiconductor in Se rich condition, while Sb2S3 is an intrinsic semiconductor without significant free carrier density. Additionally, due to the unique quasi-1D structures and strong electron–lattice coupling, antimony chalcogenides are able to accommodate larger lattice relaxation than conventional 3D bulk crystals, resulting in negative-U behavior in their defect structures. Therefore, the competing superior electronic structure and complex defect chemistry suggest that, while antimony chalcogenides are excellent photoabsorbers, effort shall be made to suppress the formation of the detrimental native defects to further improve their open-circuit voltage, electronic transport, and, thus, power conversion efficiency.

Theoretical insight into the anion vacancy healing process during the oxygen evolution reaction on TaON and Ta3N5.

Anion vacancies are common defects in materials, and they are usually much more stable on the outermost surface. These vacancies are sometimes taken as active sites in some reactions during catalysis. During the oxygen evolution reaction (OER), these vacancies may be healed by oxygen atoms from water. But this healing process is not well understood yet. In this work, we investigated the details of the anion vacancy healing process in the OER using TaON and Ta3N5 as models. In the OER process, we found that the vacancies are stable and cannot be healed without an applied potential. But with the equilibrium potential of 1.23 V, the vacancies on the outermost top surface will be healed. The oxygen vacancies, after healing, revert back to a clean surface. The nitrogen vacancies become an oxygen doped surface after vacancy healing. We also investigated the vacancy healing process on other well-known photocatalysts, like TiO2, BiVO4, WO3, α-Fe2O3, NaTaO3 and SrTiO3, and we found that the vacancies on the top surface of these materials will also be healed in the OER with an applied equilibrium potential of 1.23 V. The results presented here could expand to other materials used for the OER in (photo) electro-catalysis and photocatalysis. This work provides a new insight for understanding the role of vacancies in the OER.

Surface Cationic and Anionic Dual Vacancies Enhancing Photocatalytic Activity of Bi2wo6

Surface Cationic and Anionic Dual Vacancies Enhancing Photocatalytic Activity of Bi2wo6

Understanding and controlling the formation of surface anion vacancies for catalytic applications

Systematic computational efforts aimed at calculating surface anion vacancy formation energies as important descriptors of catalytic performance are summarized.

Structural characteristics, cation distribution, and elastic properties of Cr3+ substituted stoichiometric and non-stoichiometric cobalt ferrites.

Structural, elastic and cation distribution properties have been investigated on stoichiometric and non-stoichiometric cobalt ferrites. Crystal structure, formation of spinel type ferrite, chemical bonding, cation distribution, and thermal properties of two series of Cr3+ substituted stoichiometric and non-stoichiometric various cobalt ferrites with general formula Co1−xCrxFe2O4 (S1), and Co1+xCrxFe2−xO4 (S2) were reported. Samples are synthesized by the solid-state reaction technique via planetary ball milling. X-ray diffraction (XRD) analysis confirms the formation of a single phase cubic spinel structure with the space group Fd3̄m. Rietveld refinement results show that Cr occupies both the tetrahedral (A-site) and octahedral sites (B-site). The experimental lattice parameters show increasing trends for both the series with increase of Cr content. The cation–anion vacancies, chemical bonding, and the displacement of oxygen have been evaluated to understand the effect of Cr substitution and how the non-stoichiometry affects the physical and chemical properties of the material. The crystallite size is found to be the decreasing value with an increase of Cr concentration for both series of samples. Specific vibrational modes from the FTIR spectra suggest a gradual change of inversion of the ferrite lattice with the increase of Cr concentration which is also evident from Rietveld refinement data. The elastic properties analysis reveals that the synthesized samples for both series are ductile in nature. The non-stoichiometric structure with excess Co2+ may pave a new way to realize the lowering of Curie temperature of ferrite that is expected to improve the magnetocaloric properties.

Achieving superior lithium storage performances of CoMoO4 anode for lithium-ion batteries by Si-doping dual vacancies engineering

Regarded as a promising anode material, CoMoO4 can reveal higher theoretical capacity (980 mAh g−1) in the context of completely reversible electrochemical reaction. Unfortunately, the large volume expansion, low conductivity and inferior cyclic stability are non-negligible, which have greatly limited its further development and application. Herein, a series of CoMo1-xSix/2O4-2x (x = 0, 0.1, 0.15, 0.2 and 0.25) anode materials have been successfully synthesized through a solid-state method. This heterovalent atom doped strategy can not only provide cationic vacancy (Mo vacancy) but also generate anionic vacancy (O vacancy). The results demonstrate that all the Si doped CoMoO4 samples exhibit superior electrochemical performances than that of the pure CoMoO4 although the produce of the dual vacancies has negligible influence on the microstructures of CoMoO4, which should be attributed to the synergistic effect of the Mo vacancy and O vacancy and thus leading to the lower optical band gap, the enhanced conductivity and the faster transport of lithium ions and electron. Particularly, when the content of Si-doping is set as 0.05, the obtained CoMo0.9Si0.05O3.8 sample displays the highest capacity (847.4 mAh g−1) up to 300 cycles at a current density of 200 mA g−1. This work paves an effective strategy for constructing dual vacancies to promote the electrochemical performance of transition metal oxide anode materials.

Interfacial defect passivation by novel phosphonium salts yields 22% efficiency perovskite solar cells: Experimental and theoretical evidence

AbstractWe modified perovskite/Spiro‐OMeTAD interface by using two novel phosphonium salts containing PF6− counter anion (i.e., ClTPPPF6 and BrTPPPF6). The cation and anion in phosphonium salts possess not only ionic bonds but also coordination bonds with perovskites. The anion and cation vacancies at the surface and GBs of perovskite films can be filled by phosphonium cations and PF6− anions, respectively, resulting in reduced defect density and prolonged carrier lifetimes. The stronger chemical interaction and accordingly better defect passivation were certified for BrTPPPF6 than ClTPPPF6. As a result, the devices modified by ClTPPPF6 and BrTPPPF6 deliver a PCE of 21.73% and 22.15%, respectively, which far exceed 20.6% of the control device. The unsealed BrTPPPF6 modified device maintains 98.2% of its initial efficiency value after thermal aging of 1320 h whereas merely 84.7% for the control device. 96.4% of its original efficiency was retained for BrTPPPF6‐modified device after ambient exposure of 2016 h.image