Search

Copper iodide (CuI) has garnered considerable attention as a promising alternative to p‐type transparent conducting oxides owing to its low cation vacancy formation energy, shallow acceptor level, and readily modifiable conductivity via doping. Although sulfur (S) doping through liquid iodination has exhibited high efficacy in enhancing the conductivity with record high figure of merit (FOM) of 630 00 MΩ−1, solution‐processed S‐doped CuI (CuI:S) for low‐cost large area fabrication has yet to be explored. Here, a highly conducting CuI:S thin‐film for p‐type transparent conducting electrode (TCE) is reported using low temperature solution‐processing with thiourea derivatives. The optimization of thiourea dopant is determined through a comprehensive acid‐base study, considering the effects of steric hindrance. The modification of active groups of thioureas facilitated a varying carrier concentration range of 9 × 1018–2.52 × 1020 cm−3 and conductivities of 4.4–390.7 S cm−1. Consequently, N‐ethylthiourea‐doped CuI:S exhibited a FOM value of 7 600 MΩ−1, which is the highest value among solution‐processed p‐type TCEs to date. Moreover, the formulation of CuI:S solution for highly conductive p‐type TCEs can be extended to CuI:S inks, facilitating high‐throughput solution‐processes such as inkjet printing and spray coating. [ABSTRACT FROM AUTHOR]

Metal oxide semiconductors have several advantages over conventional Si-based materials, including high mobility even in the amorphous state, excellent optical transparency, and compatibility with low-cost fabrication processes. Despite the toxic nature of cadmium compounds, the excellent electrical and optical properties of CdO have attracted research attention for potential applications in high-performance military and aerospace technologies. In this study, an amorphous cadmium gallium oxide (a-CdGaO)-based thin-film transistor (TFT) (optimized at Cd : Ga ratio of 5.5 : 4.5) is demonstrated, with a maximum mobility of 17.68 (14.10 in average) cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) of 1.01 × 109, a threshold voltage (Vth) of 0.73 V, optical transmittance (T550) > 90%, a bias stability of 4.36 V under positive bias stress (PBS), a bias stability of −1.83 V under negative bias stress (NBS), and a high frequency of 250 kHz when applied on a seven-stage oscillator ring circuit. Additionally, the optimized a-Cd5.5Ga4.5O12.25 device showed excellent stability over time with negligible change of mobility and Vth values after one week exposure to ambient air condition. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have attracted a considerable amount of research attention with significant progress made in the field of optoelectronics. Despite their outstanding electrical characteristics, structural defects impede their potential performance due to the polycrystalline nature of solution‐processed perovskite films. Herein, the effective p‐type doping and defect passivation of phenethylammonium tin iodide ((PEA)2SnI4) perovskite films using xanthate additives as a sulfur source is reported. Sulfur can be introduced to the iodine vacancies mainly at the grain boundaries of the perovskite film, passivating the electrical defects originating from the iodine vacancy and increasing the hole concentration. The Fermi‐level shift toward the valence band maximum of the sulfur‐doped perovskite film is confirmed using ultraviolet photoemission spectroscopy, resulting in p‐type doping. Finally, the electrical performance improvement for the 0.2% sulfur‐doped (PEA)2SnI4 thin‐film transistor with a mobility of 1.45 cm2 V−1 s−1, an on/off ratio of 2.9 × 105 is demonstrated, and hysteresis of 10 V is reduced. [ABSTRACT FROM AUTHOR]

Metal oxide thin film transistors have received tremendous attention due to various advantages over the conventional Si-based TFT for the next-generation wearable electronics. However, the surface of a metal oxide thin film is very sensitive to ambient molecules such as moisture and oxygen, degrading the device performance after long-term operation. In this work, we report on utilizing the passivation effect from various phosphonic acids (PAs) to suppress the adsorption of ambient chemical species and the oxygen vacancy defect in the superlattice (SL) structure prepared by insertion of PA between two nanocrystalline In-Ga-O (nc-IGO) layers (7.5% atomic percentage). The most effective stabilization of SL structure is successfully realized with 1,10-decyl diphosphonic acid (P10) treatment. Very impressively, the reference device with pristine nc-IGO film around 10 nm shows a large threshold voltage (Vth) shift of 11.80 V after 10,000 s of PBS (VG = 50 V, VDS = 25 V), but the optimized device with P10 SL structure with similar thickness shows a negligible Vth of 1.21 V with same stress condition. Furthermore, the oxygen vacancy defect suppression also resulted in a small Vth shift of 2.94 V after 10,000 s NBS (VG = −50 V, VDS = −25 V). [ABSTRACT FROM AUTHOR]

Transparent oxide semiconductors are successfully implemented as thin‐film transistors (TFTs) for large‐area display applications with superior electrical performance in comparison with that of conventional amorphous silicon. However, further development of high‐performance oxide semiconductors is hindered by the trade‐off between mobility and stability. Mixed metal composition containing heavy metal cations shows high‐mobility/low‐stability and light metal cations exhibits low‐mobility/high‐stability. A novel material design strategy for realizing a high‐performance oxide semiconductor for TFTs through partial substitution of Se or S for O in In2O3 is reported. In contrast to the conventional small‐sized Ga substitution for suppressing oxygen vacancies, the replacement of O by Se or S results in lattice stabilization and oxygen‐vacancy suppression, consequently stabilizing Se‐ or S‐incorporated In2O3 TFTs. In2O3:Se TFTs exhibit an average field‐effect mobility of 6.1 cm2 V−1s−1, ON/OFF current ratio (Ion/Ioff) of 108, and excellent operational stability with threshold voltage shift values of <0.10 V at a positive and negative bias stress for 10 000 s. Furthermore, the seven‐stage ring oscillator circuit operating at a supply bias of 20 V exhibits an oscillation frequency of >805 kHz and a corresponding propagation delay of <90 ns per stage. [ABSTRACT FROM AUTHOR]

A synthesis of EuO was carried out through the thermal reduction of Eu2O3 by a stoichiometric quantity of metallic Eu. EuO undergoes a second-order phase transformation at ~69 k from the ferromagnetic to the paramagnetic state on heating as indicated by the heat capacity and magnetic measurements.

Copper iodide (CuI) has gained attention as a highly conductive p-type transparent material. Here, we investigate the phase stability of I-rich cubic CuI phases with Cu-vacancy defects by performing hybrid-density functional theory calculations. In the Cu-rich equilibrium condition, the nearly stoichiometric phase is the ground state with quenched Cu-vacancy defects, and the Cu-vacancy defect is a major acceptor responsible for the intrinsic p-type conductivity. In contrast, in the I-rich condition, the off-stoichiometric Cu1−xIx phase (x = 0.5–0.55) containing high-density Cu vacancies is stabilized with configuration entropy from Cu vacancies. As the off-stoichiometric phases contain high-density neutral Cu vacancies, the hole transport can be hindered, and the hole mobility could be reduced. [ABSTRACT FROM AUTHOR]

Diacene-fused thienothiophenes (DAcTTs) have provided an excellent π-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transport characteristics remain largely unexplored. Herein, a series of functionalized low LUMO (lowest unoccupied molecular orbital) [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)2C7, and D(C7CC(CN)2)-BTBT, have been developed. Detailed structural, physicochemical, optoelectronic, and single-crystal characterization were performed. The new molecules exhibit large optical band gaps (∼2.8–3.1 eV) and highly stabilized (−ΔELUMO = 1.2–1.4 eV)/π-delocalized LUMOs as compared to p-type DAcTTs. Symmetric functionalization is found to be important to enable strong intermolecular interactions in the solid-state. All molecules exhibit alternately stacked layers of "F–BTBT–F" and "S" (F: functional group/S: substituent) with strong herringbone-like interactions (2.8–3.6 Å distances) between π-cores. While carbonyls, regardless of the substituent, adopt nearly coplanar π-backbones with BTBT, dicyanovinylenes are found to be twisted (47.5°). The conformational difference at the molecular level has unusual effects on the π-electron deficiencies, frontier molecular orbital energetics, thermal/photophysical properties, and π-electronic structures. Dicyanovinylenes at the 2,7 positions, despite twisted conformations, are shown for the first time to yield good electron transport in DAcTTs. The D(C7CC(CN)2)-BTBT thin film exhibits large 2D plate-like crystalline grains (∼1–2 μm sizes) of terraced islands and becomes a rare example of an n-type DAcTT in organic field-effect transistors (OFETs). Although a stabilized/π-delocalized LUMO, largely governed by functional groups and intramolecular twists, is essential for electron transport, our findings suggest that it should be combined with proper substituents to yield a favorable three-dimensional BTBT/functional group π-electronic structure and a low intramolecular reorganization energy. Combined with our first n-type DAcTT semiconductor D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs. The molecular engineering perspectives presented in this study may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics. [ABSTRACT FROM AUTHOR]

Thiostannate ammonium chalcogenide aerogel (TAC) is synthesized through a unique self-crosslinking polymerization reaction between tetrahedral thiostannate dimer clusters ([Sn2S6]4−) and various ammonium ligands (NR4+). TAC is a unique and rare chalcogenide aerogel (so called "chalcogel") stabilized without using a cationic transition metal center. In-depth and synergistic structural analyses reveal that after the self-condensation reaction, the thiostannate clusters are stabilized into a three-dimensional solid network with the support of an ammonium spacer. Consequently, thiostannate coordination is successfully transformed from tetrahedral to a distorted trigonal bipyramidal geometry, yielding a [Sn3S7]2− cluster-based porous chalcogenide network. This organic/inorganic heterostructure has a large specific surface area (158–363 m2 g−1), macroscopically random orientation of pores, soft basicity, controllable hosting ammonium ligand, and rapid mass transport through multiscale channels. These characteristics enable remarkable radionuclide control functionality such as large Cs+ adsorption capacity (141–220 mg g−1), high selectivity towards cations with intermediate chemical hardness (e.g., Cs+), structural integrity over a wide pH range (2–8), and rapid ion uptake (50% in 30 min and complete equilibrium within 3 h). This study demonstrates that the self-crosslinking mechanism of chalcometallate clusters can be utilized as a diverse platform to synthesize a broad range of chalcogenide heterostructures with desirable functionalities. [ABSTRACT FROM AUTHOR]

The mixed-valence compound Eu3O4 was prepared by heating an equimolar mixture of EuO and Eu2O3 at 1800 °C for 30 h in a sealed tungsten crucible. Room temperature x-ray powder diffraction measurements showed that Eu3O4 is single phase. Magnetic measurements on polycrystalline Eu3O4 are in good agreement with the results reported previously. The heat capacity of Eu3O4 from ∼2 to 300 K was not reported in the past. The magnetocaloric effect in Eu3O4 was measured for different applied magnetic fields. The magnetic entropy change (-ΔSmag) calculated from heat capacity data of Eu3O4 is approximately 12.7 J/kg K at 6.5 K for a magnetic field change (ΔB) of 5 T. The adiabatic temperature change (ΔTad) in Eu3O4 at 7 K is about 7.0 K for a ΔB of 5 T. Also, the magnetic entropy change (-ΔSmag) calculated from magnetization data in Eu3O4 is approximately 13.6 J/kg K at 6.3 K for a magnetic field change (ΔB) of 5 T, which is slightly higher than that from the heat capacity data, but is within experimental error. A metamagnetic transition was observed between 0.3 and 0.5 T, however, some antiferromagnetic correlations appear to exist in the magnetically induced ferromagnetic phase at B>3 T. [ABSTRACT FROM AUTHOR]

The mixed-valence compound Eu3O4 was prepared by heating an equimolar mixture of EuO and Eu2O3 at 1800 °C for 30 h in a sealed tungsten crucible. Room temperature x-ray powder diffraction measurements showed that Eu3O4 is single phase. Magnetic measurements on polycrystalline Eu3O4 are in good agreement with the results reported previously. The heat capacity of Eu3O4 from ∼2 to 300 K was not reported in the past. The magnetocaloric effect in Eu3O4 was measured for different applied magnetic fields. The magnetic entropy change (-ΔSmag) calculated from heat capacity data of Eu3O4 is approximately 12.7 J/kg K at 6.5 K for a magnetic field change (ΔB) of 5 T. The adiabatic temperature change (ΔTad) in Eu3O4 at 7 K is about 7.0 K for a ΔB of 5 T. Also, the magnetic entropy change (-ΔSmag) calculated from magnetization data in Eu3O4 is approximately 13.6 J/kg K at 6.3 K for a magnetic field change (ΔB) of 5 T, which is slightly higher than that from the heat capacity data, but is within experimental error. A metamagnetic transition was observed between 0.3 and 0.5 T, however, some antiferromagnetic correlations appear to exist in the magnetically induced ferromagnetic phase at B>3 T. [ABSTRACT FROM AUTHOR]

Topological crystal insulators (TCIs) that have an even number of topologically protected Dirac bands driven by crystalline mirror symmetry have attracted much attention in condensed matter physics. Here, we demonstrate that a weak disordering in the topological crystalline state can enhance thermoelectric performance significantly due to highly dispersive band dispersion and high band degeneracy which guarantee high electrical mobility and a high Seebeck coefficient, respectively. When we perturb a crystalline mirror symmetry by Se-doping in TCI Pb0.5Sn0.5Te1 −xSex, the topological state becomes weak so that it eventually evolves the normal state. We experimentally prove the topological phase transition concerning Se concentration by X-ray Absorption Spectroscopy (XAS) and extended X-ray absorption Fine Structure (EXAFS) analysis. Small crystalline perturbation by Se doping (x = 0.05) significantly enhances thermoelectric performance due to the simultaneous enhancement of electrical conductivity and the Seebeck coefficient. Therefore, we report an exceptionally high ZT value of 1.9 at 800 K for the x = 0.05 compound which is a 313% enhancement of ZT compared with the pristine compound. This research proposes a new strategy for exploring high-performance thermoelectric materials by weak disordering of topological crystalline Dirac semimetals. [ABSTRACT FROM AUTHOR]

The solution processing of crystalline VO 2 thin films has been intensively investigated for both fundamental studies and various electronic applications. However, previous studies have reported that the inevitable oxidation of vanadium cations in conventional precursor solutions hinders facile and reliable fabrication of VO 2 thin films. Here we develop a kinetically stabilized precursor solution for solution-based VO 2 thin-film fabrication. The stabilized solution precursor showed increased resistance to uncontrolled vanadium oxidation compared to conventional precursors. The synthetic conditions necessary for reliable VO 2 thin-film fabrication were investigated at various oxygen concentrations and various annealing atmospheres. The oxygen level of an ambient atmosphere controls which of the three vanadium oxidation states arise, including V 3 + , V 4 + , and V 5 + at a given temperature. The unusual occurrence of V 3 + can be obtained without any reducing reagents. Nano-crystalline VO 2 thin films subjected to rapid thermal shock exhibit metal-to-insulator transition at 58.9 °C and resistive switching in a metastable state at 53.5 °C, which could be further applied to future electronic devices such as memristors, Mott transistors, and Mott memories. [ABSTRACT FROM AUTHOR]

Abstract: Here, the preparation of transparent amorphous oxide semiconductor (AOS) films with unprecedented conductivity via an optimized activation process under hydrogen atmosphere for applications in solution‐processed large‐area optoelectronics is reported. Owing to their high cost and mechanical vulnerability, conventional vacuum‐processed indium–tin oxide (ITO) electrodes are inappropriate for use in next‐generation flexible and wearable electronic devices and systems. As an alternative to the ITO electrodes, solution‐processed AOS films, such as a‐IZO and a‐ZITO, with an optimized composition and postreduction treatment under hydrogen show the highest electrical conductivity of ≈300 S cm−1 and a high optical transmittance of over 90% at 550 nm. The microstructures and electrical properties of these AOS films are also studied in order to determine the optimized chemical composition and postreduction conditions. It is found that a controlled hydrogen reduction treatment of AOS films is critical for achieving high electrical conductivity by suppressing the surface morphology degradation and grain boundary disconnection. Furthermore, the a‐IZO transparent conductive electrodes are successfully implemented for high efficiency organic photovoltaic cells based on the PTB7/PC71BM active layers. This technique promises the low‐cost fabrication of high mobility and/or conductive AOSs for their applications in large‐area transparent and flexible optoelectronics. [ABSTRACT FROM AUTHOR]

Two Zintl phase thermoelectric compounds of Eu11−xKxBi10−ySny (x = 0, 0.26(1); y = 0.86(2), 1.93(2)) have been synthesized by a high-temperature solid-state reaction and arc-melting methods. The two isotypic crystal structures are characterized by both single-crystal and powder X-ray diffractions, and adopt a tetragonal Ho11Ge10-type structure (space group I4/mmm, Z = 2, Pearson code tI84) containing nine crystallographically independent asymmetric atomic sites in a unit cell. The chemical compositions are confirmed by EDS analysis. The complex crystal structure of the two title compounds can be described as an assembly of three different types of co-facial polyhedra formed by cations and 3-dimensional anionic frameworks surrounding these polyhedra. A quaternary title compound, Eu10.74(2)K0.26Bi9.14(2)Sn10.86, which simultaneously contains both cationic and anionic p-dopants in a single compound, was successfully crystallized for the first time in the A11M10 (A = alkaline-earth metals, rare-earth metals; M = triels, tetrels, pnictogens) series. In particular, two different types of p-dopants K and Sn show particular site-preferences, respectively, where K and Sn prefer to occupy the cationic Wyckoff 4e site and the anionic Wyckoff 8h site. These noticeable site preferences can be elucidated by either a size-factor criterion for the K-doping case or by an electronic-factor criterion for the Sn-doping case. The tight-binding linear muffin–tin orbital calculations show that as the double p-doping is applied to the Eu11−xKxBi10−ySny system, some extra holes are generated on the electronic structures according to the density of states curves. However, a series of thermoelectric property measurements prove that this extra hole-carrier doping is hardly effective enough to completely suppress a bipolar conduction of holes and electrons due to the rigid metallic band structure of the title system. [ABSTRACT FROM AUTHOR]

The effect of d1 impurity doping in Sr-hexaferrite (SrM) on the magnetic anisotropy is investigated. First-principles calculations revealed that group-V elements (V, Nb) are stabilized with co-doping of alkali elements. Na1+/K1+ doping at Sr2+-site is found to be critical to form the d1 impurities at Fe-site. Experimentally, Na-V doped SrM shows the intrinsic coercivity of ∼5.4 kOe, which is ∼300% enhancement compared to undoped SrM and comparable value to La-Co co-doped SrM. Finally, the spin-orbit coupling from non-vanishing angular momentum of d1 impurity in SrM should be a main factor for such a substantial improvement of intrinsic coercivity. [ABSTRACT FROM AUTHOR]

Thelayered perovskite compounds NaLnTiO4(Ln= Y, La–Tb) have Ln2O2rock-salt layers alternating with Na2O2rock-salt layers on either side of a TiO2sheet.The cation ordering introduces an internal electricfield perpendicular to the layers. Ion exchange of Li+forNa+changes the rock-salt Na2O2layersinto OLi2O antifluorite layers but does not change thecharge of the layers or, significantly, the internal electric field.The internal fields induce a ferroic displacement of the Ti(IV) ionstoward the alkali-ion layers. Reversible Li insertion is observedin both NaLixLnTiO4and Li1+xLnTiO4with 0 ≤ x≤ 1; the voltageprofiles show Ti(IV)/Ti(III) redox plateaus at 0.5 and 0.1 V vs Li+/Li0and a 4f6/4f7Eu3+/Eu2+plateau at 0.8 V vs Li+/Li0. The shift of 1 eV in the Ti(IV)/Ti(III) redox energy relativeto that found in the spinel Li4Ti5O12could be attributed to a capacitance energy associated with theformal +2eand −2echargeson the Ln2O2layers and thealkali-ion layers, respectively. Optical measurements showed thatthe energy gap between the Ti 3d0and O 2p6bandedges is not significantly different in the layered and spinel titanates. [ABSTRACT FROM AUTHOR]

Compounds of CuxBi2Te3(0 ≤ x≤ 0.1) were studied to measure the effect of Cu intercalation on their thermoelectric properties. HR-TEM images of freshly fractured surfaces of Cu0.07Bi2Te3showed that Cu nanoparticles formed in the van der Waals gaps between Te layers in Bi2Te3. Such nanoparticles acted as electron donors, changing the native p-type character of Bi2Te3to n-type. They also acted as phonon scatters, reducing thermal conductivity. Cu0.07Bi2Te3had high electrical conductivity of 681 S cm−1and Seebeck coefficient of −236 μV K−1with low thermal conductivity of 1.0 W m−1K−1, thus enhancing the figure of merit, ZT, to 1.15 at approximately 300 K. The intercalation of metal nanoparticles between Te layers in Bi2Te3is a promising strategy for the preparation of highly efficient n-type thermoelectric materials. [ABSTRACT FROM AUTHOR]

Correction for 'Thiostannate coordination transformation-induced self-crosslinking chalcogenide aerogel with local coordination control and effective Cs+ remediation functionality' by Yeo Kyung Kang et al., J. Mater. Chem. A, 2020, 8, 3468–3480, DOI: 10.1039/C9TA11282K. [ABSTRACT FROM AUTHOR]

We report an electrical and thermal transport study for polycrystalline samples of In4Se3-x substituted with various metals. Our experimental and theoretical investigation revealed that the Na, Ca, and Pb substitutions at the In4 site in the 4:3 indium selenide lattice are more effective for increase in electron concentration than the Zn, Ga, and Sn substitutions at other sites, and the Peierls distortion in cationic substituted compounds may not be as strong as In4Se3-x based on higher lattice thermal conductivities of the former than the latter. It is found that the cationic substitutions may weaken the effect of Peierls distortion on thermal properties for In4Se3-x while they maintain the same trend for electrical properties of In4Se3-x with different electron concentrations. [ABSTRACT FROM AUTHOR]

We present thermoelectric properties and electronic structure of the series compounds of In4Se3-xTex (0.0≤x≤3.0). Even if the Te-doping is an isoelectronic substitution, we found that the electron dominated carrier transport in Se-rich region (x≤0.2) evolves into the electron-hole bipolar transport properties in Te-rich region (x≥2.5) from the temperature-dependent thermal conductivity κ(T), Seebeck coefficient S(T), and Hall coefficient RH(T) measurements. The electronic band structures of In4Se3-xTex (x=0.0, 2.75, and 3.0) are not changed significantly with respect to Te-substitution concentrations. From the Boltzmann transport calculation, the electron-hole bipolar effect on thermoelectric transport properties in Te-rich region can be understood by lowering the chemical potential to the valence band maximum in the Te-rich compounds. [ABSTRACT FROM AUTHOR]