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Herein, the structural, optical, and magnetic properties of Y0.85La0.15FexAlyO3: (x; y) where x = 1; y = 0, x = 0.975; y = 0.025, x = 0.95; y = 0.05, and x = 0.9; y = 0.1 nanomaterials obtained from sol–gel method are reported. The X‐ray powder diffraction (XRD) for the structural characterization, scanning electron microscopy for crystallite size estimation, ultraviolet–visible absorption for optical studies, and vibrating‐sample magnetometer for magnetic studies are used in this investigation. An increase of orthorhombic crystal structure with an increase of Al content in the sample is observed from XRD studies. The existence of all the elements present in the samples is observed from energy‐dispersive X‐ray spectroscopy. The optical bandgap increases from 2.04 to 2.10 eV with an increase of Al concentration from 0 to 0.05. The observed magnetization value is 3.14 emu g−1 for y = 0.05, which is higher than y = 0 (2.11 emu g−1) and y = 0.024 (2.58 emu g−1). In summary, the obtained result (x = 0.95; y = 0.05) can be useful for different magnetic‐based applications. [ABSTRACT FROM AUTHOR]

The recent year has witnessed a flurry of activities in investigating the promising electronic, optical, and transport properties of lead‐free double perovskite halides. In the present work, the structural, electronic, optical, and transport properties of Cs2(Li/Na)GaI6 are carefully examined. The predicted negative formation energy, absence of imaginary frequency in the phonon spectra, and ab‐initio molecular dynamics calculations show that they are thermodynamically stable. Additionally, electronic studies employing generalized gradient approximation (GGA)–Perdew–Burke–Ernzerhof (PBE) + modified Becke‐Johnson + spin‐orbit coupling reveal that Cs2(Li/Na)GaI6 exhibits a direct bandgap, with values of 1.24 eV for Cs2LiGaI6 and 1.39 eV for Cs2NaGaI6. The exceptional optical properties, including a high absorption coefficient (105 cm−1) and excellent optical conductivity with low reflectivity across the entire UV–visible range, indicate that Cs2(Li/Na)GaI6 are promising materials for solar cell applications. Moreover, the ultralow thermal conductivity, high Seebeck coefficient, and substantial electrical conductivity of Cs2(Li/Na)GaI6 result in a high figure of merit over the temperature range of 200–600 K. Thus, Cs2(Li/Na)GaI6 shows strong potential as both photovoltaic and thermoelectric materials. [ABSTRACT FROM AUTHOR]

An optical spectroscopy study is reported of single crystals of the LiNbO3–LiTaO3 solid solution. The spectra are dominated by the fundamental absorption edges. The direct band‐to‐band transitions in congruent LiNbO3 (LN) and LiTaO3 (LT) as well as in selected compositions of solid solutions grown from mixtures of the congruently melting end members are studied at temperatures up to 1200 °C. At room temperature, the direct optical bandgaps of congruent LN and LT assume values of about 4.0 and 4.6 eV, respectively. With rising temperatures, the absorption edges are found to shift to lower energies. The isothermal composition dependence of bandgaps is a far from linear by going through a minimum. This behavior is maintained up to the highest temperatures of our study. At about 600 °C, congruent LT undergoes a structural transition from the ferroelectric to the paraelectric phase. This is reflected by a change in the temperature dependence of the gap energy indicating structure‐related changes in electron–phonon coupling. [ABSTRACT FROM AUTHOR]

Bulk ferroelectrics hold tremendous potential for the rapidly growing field of photovoltaic applications due to the separation of charge carriers caused by polarization, resulting in a high photovoltage. However, the wider bandgap in ferroelectrics limits their photoresponse. Attempts to tune the bandgap degrade ferroelectric polarization, while increased oxygen vacancy (Vo¨$\overset{\cdot\cdot}{\text{o}}$) in oxide perovskite hinders electron conduction and undermines ferroelectricity. Therefore, controlling Vo¨$\overset{\cdot\cdot}{\text{o}}$ and maintaining polarization in reduced bandgap ferroelectric photovoltaics remains challenging. To address this, aliovalent Fe3+ and Nb5+ are co‐substituted on the B‐site of Na0.5Bi0.5TiO3 ceramics. Various techniques confirm the controlled Vo¨$\overset{\cdot\cdot}{\text{o}}$ concentration, and UV‐absorption data reveal a reduction in bandgap energy from 3.01 to 2.38 eV through metal substitution. Density functional theory calculations identify a localized intermediate gap state within the bandgap, created by Fe–O hybridization, acting as a charge carrier scaffold and further reducing the bandgap energy to 2.47 eV. Remarkably, the Al/NBFNT75/Ag configuration achieves an augmented short‐circuit current density of 18.92 nA cm−2, while the open‐circuit voltage of the Al/NBFNT50/Ag device reaches 4.13 V. The resulting Al/NBFNT75/Ag device exhibits a maximum photovoltaic power density of 0.725 mW m−2 which is 9.5 times greater than Al/Na0.5Bi0.5TiO3/Ag. This approach successfully reduces Vo¨$\overset{\cdot\cdot}{\text{o}}$ and achieves narrow bandgap conditions through suitable aliovalent substitution, leading to enhanced photovoltaic power, photosensing response, photoresponsivity, and specific detectivity. [ABSTRACT FROM AUTHOR]

Halide perovskites have broad bandgap tunability, making them suitable for diverse applications in optoelectronics and photovoltaics. The optical bandgap of halide perovskites varies almost linearly with the halide ionic size, and therefore, it can be controlled through compositional engineering. However, the mechanism underlying this low‐bandgap variation is not yet fully understood. Thus, this study comprehensively investigates the bandgap bowing of cesium–lead mixed‐halide perovskites using compositional engineering and demonstrates that bandgap bowing is extremely small in a variety of compositions including Cl, Br, and I. Subsequently, through density functional theory calculations, it is suggested that the antibonding character of the valence band maximum, tilt distortion of halide ions, and entropy effect leading to equal participation of various halide ions around Pb are collectively responsible for the small bandgap bowing. [ABSTRACT FROM AUTHOR]

Bifacial perovskite (PVK)/crystalline silicon (c‐Si) tandem photovoltaic (PV) modules provide an effective strategy to further improve the efficiency and energy yield (EY) of c‐Si PV modules. In this work, the energy outputs of bifacial tandem PV modules under outdoor conditions are analyzed by combining optical modeling, one‐diode equivalent circuit model, module tilt angle, and meteorological data, and a detailed comparative study with bifacial silicon heterojunction (SHJ) PV modules is also performed. The bifacial PVK/c‐Si tandem modules exhibit higher EY in locations with strong direct normal irradiance regardless of the ground type with any albedo, while bifacial SHJ modules exhibit similar or even higher EY than tandem modules in locations with strong diffuse horizontal irradiance (DHI) such as Chengdu. Considering factors such as EY and levelized cost of electricity, Eg_PVK in the range of 1.58–1.62 eV is suitable for most application scenarios, while the deployment of bifacial SHJ PV modules is preferred in areas dominated by DHI, as represented by Chengdu. Herein, important implications for policy making in determining the cost‐effective type of PV modules are provided to generate renewable electricity. [ABSTRACT FROM AUTHOR]

Using a microscopic model, the magnetic and electric properties of pure and ion‐doped (on the Lu or Fe sites) hexagonal LuFeO3 (LuFO) are studied and compared with the properties of ion‐doped LaFeO3 (LaFO). The magnetization increases by Sr and Sc doping which is caused by the strain and the changes of the exchange interaction constants at the doped states. It is observed that by Sm doping of LuFO the polarization decreases, whereas by Sm doping of LaFO, the polarization increases with increasing Sm concentration. By Ir or Co ion doping on the Fe site, the magnetization and the phonon energy increase whereas the bandgap energy decreases. By doping on the Fe sites with the same ion, for example, Sc, there are no differences between LuFO and LaFO. A good agreement with the experimental data is observed. The doping effects can be used for different applications. [ABSTRACT FROM AUTHOR]

Using a microscopic model, the magnetic and electric properties of pure and ion‐doped (on the Lu or Fe sites) hexagonal LuFeO3 (LuFO) are studied and compared with the properties of ion‐doped LaFeO3 (LaFO). The magnetization increases by Sr and Sc doping which is caused by the strain and the changes of the exchange interaction constants at the doped states. It is observed that by Sm doping of LuFO the polarization decreases, whereas by Sm doping of LaFO, the polarization increases with increasing Sm concentration. By Ir or Co ion doping on the Fe site, the magnetization and the phonon energy increase whereas the bandgap energy decreases. By doping on the Fe sites with the same ion, for example, Sc, there are no differences between LuFO and LaFO. A good agreement with the experimental data is observed. The doping effects can be used for different applications. [ABSTRACT FROM AUTHOR]

Light‐harvesting materials with dynamical management of light transmittance hold great promise in smart photovoltaics (PV). Here, a novel organic–inorganic halide, MVBi2I8 (MV = methyl viologen cation), exhibiting reversible thermochromism and constant bandgap of ≈1.65 eV over a wide temperature range of 77–453 K, is presented as a candidate. The compound consists of 0D (Bi4I16)4– clusters and MV2+ cations. And the adjacent (Bi4I16)4– clusters are in touch with each other, forming a 3D interaction for the inorganic part. The experimental and theoretical studies reveal that the ionic and covalent interactions in the crystal undergo a self‐adjusting process in response to temperature changes. The self‐adjustment and electron transfer between inorganic clusters and organic cations enable excellent reversible thermochromism and constant narrow bandgaps over a wide temperature range, which is expected for smart PV windows integrated with information displays and potentially other technologies. [ABSTRACT FROM AUTHOR]

2D materials that possess multifunctional properties are of great interest for applications in semiconducting devices. Herein, a series of novel Janus XYP2 (X/Y = Si, Ge, Sn, and Pb; X ≠ Y) monolayers with good stability, electronic, mechanical, piezoelectric properties, as well as ferromagnetic properties are predicted based on density functional theory. They are all indirect‐bandgap semiconductors with bandgaps varying from 0.56 to 2.18 eV. The monolayers exhibit in‐plane and out‐of‐plane piezoelectricity with large piezoelectric coefficients, suggesting that they are promising piezoelectric materials for nanoelectromechanical systems. In SiGeP2, GeSnP2, and SnPbP2 monolayers, hole doping is found to be an effective approach in inducing or tuning different ferromagnetic states resulting from electronic instability as reflected by van Hove singularity of band structures in the 2D systems. The results suggest that Janus XYP2 monolayers can be promising 2D materials for applications in nanoelectronic, spintronic, and nanoelectromechanical devices. [ABSTRACT FROM AUTHOR]

Herein, a structural design for labyrinthine acoustic metamaterial is proposed using a topology optimization method to realize a subwavelength bandgap preventing the transmission of low‐frequency sounds. The optimized design is composed of air‐filled channels of different widths, which exhibit the subwavelength bandgap based on the monopole resonance induced in the meta‐atom. In addition to the optimized meta‐atom design, a simplified meta‐atom design with a small coiling coefficient is proposed by extracting structural features of the optimized design. The bandwidth and central frequency of the subwavelength bandgap can be controlled by adjusting the size parameters of the simplified meta‐atom. Numerical analysis for acoustic waves based on the finite‐element method is conducted to demonstrate the low transmission coefficients of the obtained designs for a wide‐ and low‐frequency range. Furthermore, using a 3D printer, experimental specimens of optimized and simplified meta‐atoms are constructed, and impedance tube experiments are performed to show their functionality. [ABSTRACT FROM AUTHOR]

Herein, a novel star‐shaped hybrid acoustic metamaterial structure is proposed. Based on Bloch's theorem and the finite element method, the bandgap characteristics and the bandgap formation mechanism of different combinations of structures are first analyzed. Then, the propagation characteristics of elastic waves in Model C2 are studied with focus on equal frequency contours, phase velocity, and group velocity. And the attenuation of elastic waves in the finite size structure of Model C2 illustrates that the elastic waves are effectively suppressed in the bandgap frequency range, which further confirms the perfect correspondence between the bandgap and the vibration attenuation region. Finally, the influence of structural parameters on the bandgap is analyzed, as well as the change of the bandgap when the structure undergoes large deformation, which can realize the tunability and flexibility of the bandgap. This study provides important clues for the design of vibration isolators and metamaterials, and shows the good engineering application potential of the structure for vibration isolation. [ABSTRACT FROM AUTHOR]

Designing artificial microstructural metamaterials that fulfill the single‐phase vibration dampening and lightweight twin goals is challenging and critical. 2D curved and chiral hybrid star‐shaped metamaterials (CCHSM) are proposed to perform vibration reduction filtering in the midfrequency region by combining the properties of chiral structure and concave structure. The generating process of the bandgap of in‐plane elastic waves, the properties of directional attenuation, and the flow direction of energy in the dispersion curve are examined using the modal shape, dispersion surface, and group velocity. In a specific frequency range, the equivalent medium parameters satisfy the conditions of negative refraction transverse and longitudinal waves, so the structure also has double‐negative characteristics. The filtering performance is validated using the CCHSM periodic plate structure and a finite‐element simulation of transmission loss. In addition, the correlation between wave attenuation characteristics and structural parameters is explored. The radius of the circular arc and the deflection angle of the connecting rod have a significant impact on the frequency range of the structural bandgap. The results show that the created simple‐configured, single‐phase lightweight acoustic metamaterials exhibit strong local resonance properties and double‐negative features. [ABSTRACT FROM AUTHOR]

In solid state physics, a bandgap (BG) refers to a range of energies where no electronic states can exist. This concept was extended to classical waves, spawning the entire fields of photonic and phononic crystals where BGs are frequency (or wavelength) intervals where wave propagation is prohibited. For elastic waves, BGs are found in periodically alternating mechanical properties (i.e., stiffness and density). This gives birth to phononic crystals and later elastic metamaterials that have enabled unprecedented functionalities for a wide range of applications. Planar metamaterials are built for vibration shielding, while a myriad of works focus on integrating phononic crystals in microsystems for filtering, waveguiding, and dynamical strain energy confinement in optomechanical systems. Furthermore, the past decade has witnessed the rise of topological insulators, which leads to the creation of elastodynamic analogs of topological insulators for robust manipulation of mechanical waves. Meanwhile, additive manufacturing has enabled the realization of 3D architected elastic metamaterials, which extends their functionalities. This review aims to comprehensively delineate the rich physical background and the state‐of‐the art in elastic metamaterials and phononic crystals that possess engineered BGs for different functionalities and applications, and to provide a roadmap for future directions of these manmade materials. [ABSTRACT FROM AUTHOR]

Minimal cost, huge area, high throughput, high performance of photovoltaic panels, prolonged lifespan, and less toxicity are vital aspects when transitioning photovoltaic technology from lab‐scale production to industrial implementations. A new class of materials typically known as hybrid halide double perovskites (HHDPs) has emerged as a possible alternative for the replacement of toxic lead in crystal lattice for realizing lead‐free, stable, and high‐performance perovskite solar cells (PSCs). An ab initio analysis of (MA)2AgInBr6 HHDP via the WIEN2K code is conducted. It is found that this material has a direct bandgap of 3.85 eV having excellent optical properties in the UV region. The calculated thermodynamic parameters confirm its thermal stability at different temperatures and pressure. Its figure of merit is more than unity at room temperature as well as higher temperature ranges, so this material will be useful in thermoelectric (TE) devices as a TE material. [ABSTRACT FROM AUTHOR]

Double perovskite halide materials have been widely used in batteries, light‐emitting diodes, and solar cells. Thus, investigations of the fundamental properties of the double perovskite halide to search for an ideal structure are crucial. In this study, a surrogate model is developed to predict the formation energy, convex hull energy, and bandgap of A2BB′X6 type double perovskite halide structures. The material properties of 13 542 candidate structures are predicted and validated through first‐principles calculations. Without double perovskite halide information during training, the prediction accuracy for the formation energy is obtained as an R‐squared value of 0.770 and Root Mean Square Error (RMSE) of 0.404 eV atom−1. For the convex hull energy, an accuracy of 0.642 is obtained. For the bandgap, R‐squared score of 0.427 and an RMSE of 1.235 eV are achieved. Furthermore, the optimization process confirms that adding only 850 (6%) double perovskite halide structures to the training set increases the R‐squared value to 0.90 for the formation energy. In the bandgap, more data are needed; 3550 data (68.2%) are added to achieve an R‐squared score of 0.9. The current study successfully predicts the fundamental properties of double perovskite halides for the accelerated discovery of ideal structures. [ABSTRACT FROM AUTHOR]

Metal chalcohalides have recently been highlighted as so‐far overlooked semiconductors that could play an important role in the future of photovoltaics (PV). Indeed, the blooming field of emergent PV technologies is still in search for stable, efficient, and environmentally‐friendly light‐harvesting materials to be used either in single‐junction solar cells or multijunction devices in combination with silicon or another absorbers. Under the broad terms of metal chalcohalides, there exists a plethora of semiconductor materials with different chemical, structural, and optoelectronic characteristics. While some have already been implemented in solar cells with power conversion efficiencies up to 4–5%, others are only theoretically described. This perspective article offers a general overview of these materials as potential next‐generation absorbers in PV and also discusses possible limitations, not only related to intrinsic materials' properties but also to processing conditions. [ABSTRACT FROM AUTHOR]

Several‐nanometer‐thick, closed, and epitaxial cobalt(II) oxide films with wurtzite crystal structure (w‐CoO) are grown on Au(111) and their structural and electronic properties analyzed. The structural quality of the (0001¯) oriented, oxygen‐terminated, and unreconstructed films allow the application of surface‐science methods to unravel the properties of this unusual polymorph of CoO and may pave the way for future thin‐film applications. An experimental structural analysis by low‐energy electron diffraction (LEED‐IV) is presented with an excellent agreement between measured and calculated intensity spectra expressed by a Pendry R‐factor of R=0.112 and few‐picometer error bounds in the parameter values. Using scanning tunneling spectroscopy (STS) the bandgap of the semiconducting films is found to be 1.4 ± 0.2 eV. Ultraviolet photoelectron spectroscopy (UPS) confirms the presence of a gap and the position of the Fermi level (EF). The structural results of density functional theory calculations using (hybrid) functionals to treat electron correlations and van der Waals forces agree well with the experimentally determined structure of the antiferromagnetic w‐CoO films. In contrast to generalized gradient approximation (GGA)+U calculations, the Heyd–Scuseria–Ernzerhof hybrid functional reproduces the semiconducting nature correctly and predicts surface states in the gap which might pin EF in agreement with STS and UPS. [ABSTRACT FROM AUTHOR]

Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation‐dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density‐functional‐theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction. [ABSTRACT FROM AUTHOR]

In this research highlight, recent significant advances with hot‐assisted blade‐coating or air knife‐assisted blade‐coating of different perovskite compositions with bandgaps ranging from 1.3 eV to 1.9 eV (i.e. wide‐bandgap or small‐bandgap perovskites with mixed cations and anions, 2D/3D perovskites, Pb/Sn binary perovskites, and all‐inorganic perovskites) for single‐junction or tandem PSCs are discussed, with an emphasis on elucidating the distinct ink formulation engineering strategies, crystal growth mechanisms, crystallization kinetics, and optoelectronic properties of the different perovskite compositions. [ABSTRACT FROM AUTHOR]

Mechanical metamaterials are architected manmade materials that allow for unique behaviors not observed in nature, making them promising candidates for a wide range of applications. Existing metamaterials lack tunability as their properties can only be changed to a limited extent after the fabrication. Herein, a new magneto‐mechanical metamaterial is presented that allows great tunability through a novel concept of deformation mode branching. The architecture of this new metamaterial employs an asymmetric joint design using hard‐magnetic soft active materials that permits two distinct actuation modes (bending and folding) under opposite‐direction magnetic fields. The subsequent application of mechanical compression leads to the deformation mode branching where the metamaterial architecture transforms into two distinctly different shapes, which exhibit very different deformations and enable great tunability in properties such as mechanical stiffness and acoustic bandgaps. Furthermore, this metamaterial design can be incorporated with magnetic shape memory polymers with global stiffness tunability, which also allows for the global shift of the acoustic behaviors. The combination of magnetic and mechanical actuations, as well as shape memory effects, impart wide tunable properties to a new paradigm of metamaterials. [ABSTRACT FROM AUTHOR]

Herein, a novel wide‐band‐gap donor polymer, PBTVT, which comprises a bis(carboxylic ester)‐substituted thiophene–vinylene–thiophene (TVT) acceptor unit and benzodithiophene donor unit, is designed and synthesized. PBTVT displays good solubility in halogen‐free green solvents such as o‐xylene at elevated temperature. Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurement revealed that PBTVT can form the desired face‐on orientation in the blend films. Organic solar cells are fabricated with PBTVT as the donor and ITOIC‐2F as the acceptor. Although the highest occupied molecular orbital (HOMO) level offset between PBTVT and 2,2′‐((2Z,2′Z)‐(((4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(3,4‐bis(hexyloxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (ITOIC‐2F) is only 0.08 eV, devices still exhibit an overall power conversion efficiency (PCE) of 11.04%. Especially, devices fabricated with the green solvent o‐xylene outperform those fabricated with halogenated solvents such as 1,2‐dichlorobenzene (o‐DCB). [ABSTRACT FROM AUTHOR]

For the amorphous SiZnSnO (a‐SZTO) thin‐film transistor (TFT), Si can suppress oxygen vacancies, mainly due to higher bonding strength with O compared with Zn or Sn in amorphous oxide ZnSnO semiconductors. When these devices are driven at a low power, a nonideal transfer characteristic of hump phenomenon is observed. As Si concentration increases, this phenomenon is also found even at high voltage. The Si doping changes not only the electrical performance but also the bandgap state. As the Si concentration increases, the conduction band (Ec) raises up to vacuum level. In general, when metal and semiconductor are contacted, a band bending phenomenon occurs at a contact interface due to different work function. This change in Ec caused by the bandgap change due to Si doping also affects the band bending that can form different barriers at the interface between the metal and the channel. When low drain‐to‐source voltage (Vds) is induced, band bending can act as a barrier and cause a hump. So, the hump phenomenon is carefully observed if low Vds is applied to TFT. To make a low‐power device, the work function difference between metal and semiconductor must be considered. [ABSTRACT FROM AUTHOR]

To reveal the intrinsic relationship between the electronic structure and optical properties of YxAl1−xN alloys, a comparative first‐principles study for pure AlN and YxAl1−xN alloys is conducted. In light of the density functional theory, the arrangement of yttrium (Y) atoms in the AlN supercell is first investigated, which demonstrates that the structure of Y atoms distributed locally along the c‐axis tends to be energetically favorable, compared with the structures of Y atoms lying on the same ab plane. The lattice parameters, bandgap, density of states, and optical constants are also calculated with varied Y concentration x. The results indicate that the lattice parameters increase with the ascending x, which demonstrates the distortion of the crystal structure. Moreover, the bandgaps of YxAl1−xN are found to be affected by the arrangement of Y atoms but generally with the same trend to become narrowed by the increase in x, respectively. The optical properties of YxAl1−xN alloy are adjustable by the Y concentration x in the low energy regime and correspond to the variation in the bandgaps. The theoretical results are likewise compared with the previously reported experimental data. [ABSTRACT FROM AUTHOR]

Bandgaps of AlInN alloys, short‐period InN/AlN superlattices (SLs), and short‐period AlInN alloy SLs are calculated using first‐principles calculations with the pseudopotential self‐interaction correction method. The dependence of these bandgaps on the composition and thickness of the SLs and the influence of strain are investigated. It is found that the bandgaps of the InN/AlN SLs depend on both the composition and thickness of the SLs. The maximum value of the bandgap equal to 2.56 eV is obtained for 1InN/4AlN SLs. The bandgaps of AlInN alloy SLs decrease with an increase in In content, and they cover the whole range between the values of AlN and InN. The bandgaps of InN/AlN SLs lattice‐matched to AlN are smaller than those of free‐standing InN/AlN SLs. [ABSTRACT FROM AUTHOR]

Due to the unique bandgap tunability of bilayer graphene, the preparation of large‐sized bilayer graphene has attracted a wide range of attention. Herein, the preparation of bilayer graphene, from stacking order to growth mechanism, is reviewed, and the chemical vapor deposition (CVD) of AB‐stacked bilayer graphene on copper substrate is emphasized. Various methods and growth strategies to synthesize bilayer graphene and the corresponding growth mechanisms are discussed. Mechanisms of layer‐by‐layer growth, the hydrogen passivation of graphene edges for the formation of bilayers, and carbon atoms penetrating through a copper wall for bilayer growth are included and highlighted for a better understanding of controlling bilayer graphene uniformity and forming its stacking order. Finally, the remaining challenges and the potential development of CVD‐controlled growth of bilayer graphene are outlined. [ABSTRACT FROM AUTHOR]

The alloying behavior between FAPbI3 and CsSnI3 perovskites is studied carefully for the first time, which has led to the realization of single-phase hybrid perovskites of (FAPbI3)1− x(CsSnI3) x (0< x<1) compositions with anomalous bandgaps. (FAPbI3)1− x(CsSnI3) x perovskites exhibit stable, homogenous composition/microstructure at the nanoscale, as confirmed by microscopic characterization. The ideal bandgap of 1.3 eV for single-junction solar cell operation is achieved in the rationally-tailored (FAPbI3)0.7(CsSnI3)0.3-composition perovskite. Solar cells based on this new perovskite show power conversion efficiency up to 14.6 %. [ABSTRACT FROM AUTHOR]

A unique non-destructive characterization method for apparent bandgap imaging in photovoltaic (PV) devices based on acquisition of two electroluminescence (EL) images in different spectral ranges is presented. The method consists of a calibration procedure and a bandgap imaging procedure. Calibration has to be performed once per module type and EL imaging setup, and must provide a relation between the bandgap and the ratio between two spectrally independent EL images. After calibration, bandgap imaging only requires acquisition of two spectrally independent EL images followed by image processing, making the method very fast and suitable for in-line PV module characterization with regard to spatial (in)homogeneity and production process stability. The method is demonstrated on a commercial state-of-the-art Cu(In,Ga)Se2 PV module where apparent bandgap fluctuations between 1.07 and 1.15 eV are detected. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

MoS2/graphene (MoS2/Gr) vertical heterostructures have exhibited great application potentials in high speed electronic and optoelectronic devices, as well as efficient electrocatalysts in hydrogen evolution reaction (HER). The electronic property at the edge of monolayer MoS2 is an essential parameter for addressing such applications. Herein, it is reported that, for monolayer MoS2 synthesized on Gr/Au foils by chemical vapor deposition, a dramatic decrease of the bandgap from ≈2.20 to ≈0.30 eV occurs at the domain edge within a lateral distance of ≈6 nm, as evidenced by scanning tunneling microscopy/spectroscopy observations. The edges of monolayer MoS2 on Gr/Au foils can thus be regarded as narrow-gap quantum wires considering of their reduced bandgaps. More intriguingly, it is found that this bandgap decrease at the domain edge is closely related to the rather high HER performance for MoS2/Gr/Au foils comparing with that of MoS2/Au foils. Briefly, this work should propel the band structure investigations for MoS2/Gr stacks and their applications in energy related fields. [ABSTRACT FROM AUTHOR]

Through the labile coordination sites of a robust phosphonate-stabilized titanium-oxo cluster, 14 O-donor ligands have been successfully introduced without changing the cluster core. The increasing electron-withdrawing effect of the organic species allows the gradual reduction of the bandgaps of the {Ti6} complexes. Transition-metal ions are then incorporated by the use of bifunctional O/N-donor ligands, organizing these {Ti6} clusters into polymeric structures. The coordination environments of the applied metal ions show significant influence on their visible-light adsorption. Both the above structural functionalizations also tune the photocatalytic H2 production activities of these clusters. This work provides a systematic bandgap engineering study of titanium-oxo clusters, which is important not only for their future photocatalytic applications, also for the better understanding of the structure-property relationships. [ABSTRACT FROM AUTHOR]

The electroluminescence (EL) degradation mechanisms of organic light‐emitting devices (OLEDs) are studied utilizing phosphorescent and fluorescent materials as emitter guests. The results show that these emitter guests, despite being used in low concentrations in OLEDs, aggregate as a result of electrical stress, giving rise to the emergence of new longer‐wavelength bands in their EL spectra after prolonged device operation. Such electrical‐driving‐induced aggregation occurs more significantly in guest materials with wider bandgap (Eg) and flatter molecular structures. Further investigations reveal that the aggregation process is mainly induced by interactions between excitons and positive polarons that reside on the guests. The findings uncover a previously unknown degradation mechanism that appears to be responsible for the generally much lower EL stability of blue devices relative to their green and red counterparts, especially in case of phosphorescent emitters. [ABSTRACT FROM AUTHOR]

A photochemical route for the facile synthesis of tunable bandgap graphene‐based derivatives from graphene oxide (GO) through controlled laser irradiation in liquid phase is presented. The method is facile and fast, yielding these materials within 2 h and with excellent long‐term stability. It makes use of photogenerated‐solvated electrons that give rise to GO reduction, accompanied by preferential attachment of the desired functional unit, intentionally dispersed into the precursor GO solution. As a proof of concept, laser GO‐ethylene‐dinitro‐benzoyl (LGO‐EDNB) was photochemically synthesized and utilized as the electron acceptor material in organic bulk heterojunction solar cells (OSCs) with the poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] as the electron donor. The graphene derivatives are highly dispersible in organic solvents used in OSCs, while their energy levels can be readily tuned upon fine‐tuning of the bandgap, which is directly related to the irradiation dose applied during the synthesis process. The utilization of LGO‐EDNB with a band gap of 1.7 eV, and a resultant lowest unoccupied molecular orbital level of 4.1 eV, leads to maximum open‐circuit voltage of 1.17 V and to power conversion efficiency (PCE) of 2.41%, which is the highest PCE for graphene‐based electron acceptors to date. [ABSTRACT FROM AUTHOR]

Six conjugated polymers based on the indenopyrazine ( IPY) unit are designed and synthesized by copolymerization with different electron-deficient and electron-rich building blocks. All of the polymers show good solubility, excellent film-forming ability, and low-lying highest occupied molecular orbit (HOMO) energy levels. The effects of the different copolymerized units on the optical, electrochemical, and photovoltaic properties are investigated. Results indicate that their bandgaps and molecular energy levels are readily tuned by copolymerizing with electron-deficient and electron-rich units. Polymer solar-cell devices are fabricated utilizing the polymers as electron donors and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor. The best power conversion efficiency of the cell based on PIPY-DTBTA, one of the IPY- based polymers, reaches 0.77%, with a relatively high Voc up to 0.78 V. [ABSTRACT FROM AUTHOR]

PbTe alloys have been the most efficient materials for thermoelectric power generation since the 1950s. In addition to the observed lattice thermal conductivity reduction by alloy scattering, recent efforts targeting electronic-transport enhancement through band structure engineering have demonstrated a design route to achieve extraordinary thermoelectric performance. Guided by these recent results, the current work discusses the influence of alloying CdTe in p-type PbTe where the solubility is strongly temperature-dependent. Beneficial changes to the band structure and effective scattering of phonons are concurrently inferred when the PbTe-CdTe precipitate composite is expected to become a solid solution at high temperature, enhancing the peak thermoelectric figure of merit to ~1.7. This work emphasizes the importance of solid solution alloys of PbTe for thermoelectric power-generation applications and also provides an upper limit of about 1 micrometer to the average distance between interfaces above which phonon scattering by composite interfaces is ineffectual. [ABSTRACT FROM AUTHOR]

Three A-B-type fluorescent copolymers comprised of alternating carbazolyl and pyridinyl units, poly[(2,7-(N-(2-ethylhexyl)carbazolyl)-alt-(3,5-pyridinyl))](PEHCP-35), poly[(2,7-(N-(2-ethylhexyl)carbazolyl)-alt-(2,6-pyridinyl))] (PEHCP-26) and poly[(2,7-(N-(2-ethyl-hexyl)carbazolyl)-alt-(2,5-pyridinyl))] (PEHCP-25), are studied by means of the density functional theory (DFT/B3LYP/6-31G). Based on the optimized geometries, the optical properties are calculated by employing time-dependent density functional theory (TD-DFT). The bandgaps and optical properties are saturated quickly in PEHCP-35 and PEHCP-26. It is known from experiment that PEHCP-25 is actually an oligomer with a polymerization degree of 4. So the tetramers of PEHCP-35, PEHCP-26, and PEHCP-25 are adopted to study the electronic and optical properties, and the calculated results are in close agreement with experiment. The calculated bandgaps of copolymers obtained from two ways, i.e., HOMO–LUMO gaps and the lowest excitation energies, decrease in the following order PEHCP-35 > PEHCP-26 > PEHCP-25, the same trend as the data obtained from the edge of the electric band but different from the electrochemically obtained data from experiment (PEHCP-25 > PEHCP-26 > PEHCP-35). The outcomes showed that, when excited, a charge transfer from carbazolyl unit to pyridinyl unit occurs, and the lumophor is mainly carbazolyl units. The UV absorption and emission wavelengths both exhibit bathochromic shifts: PEHCP-35 < PEHCP-26 < PEHCP-25. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

In recent years, BiVO4 has been optimized as a photoanode material to produce photocurrent densities close to its theoretical maximum under AM1.5 solar illumination. Its performance is, therefore, limited by its 2.4 eV bandgap. Herein, nitrogen is incorporated into BiVO4 to shift the valence band position to higher energies and thereby decreases the bandgap. Two different approaches are investigated: modification of the precursors for the spray pyrolysis recipe and post‐deposition nitrogen ion implantation. Both methods result in a slight red shift of the BiVO4 bandgap and optical absorption onset. Although previous reports on N‐modified BiVO4 assumed individual nitrogen atoms to substitute for oxygen, X‐ray photoelectron spectroscopy on the samples reveals the presence of molecular nitrogen (i.e., N2). Density functional theory calculations confirm the thermodynamic stability of the incorporation and reveal that N2 coordinates to two vanadium atoms in a bridging configuration. Unfortunately, nitrogen incorporation also results in the formation of a localized state of ≈0.1 eV below the conduction band minimum of BiVO4, which suppresses the photoactivity at longer wavelengths. These findings provide important new insights on the nature of nitrogen incorporation into BiVO4 and illustrate the need to find alternative lower‐bandgap absorber materials for photoelectrochemical energy conversion applications. [ABSTRACT FROM AUTHOR]

Synergistic molecular mixing of FAPbI3 and CsSnI3 perovskites (FA=formamidinium) and formation of new crystalline alloy perovskites are reported by X. W. Sun, Y. Zhou, N. P. Padture, et al. in their Communication on page 12658 ff. The alloy perovskite of the composition (FAPbI3)0.7(CsSnI3)0.4 has an anomalous ideal bandgap of 1.3 eV for single‐junction thin‐film solar cells with an unusually high photocurrent. [ABSTRACT FROM AUTHOR]

The section shows an image which represents the Bandgap Engineering of Titanium-Oxo Clusters.