Search

Tuning electrical properties of 2D materials through mechanical strain has predominantly focused on n‐type 2D materials like MoS2 and WS2, while p‐type 2D materials such as WSe2 remain relatively unexplored. Here, the impact of controlled mechanical strain on the electron transport characteristics of both mono and bi‐layer WSe2 is studied. Through coupling atomic force microscopy (AFM) nanoindentation techniques and conductive AFM, the ability to finely tune the electronic band structure of WSe2 is demonstrated. The research offers valuable mechanistic insights into understanding how WSe2's electronic properties respond to mechanical strain, a critical prerequisite for the development of flexible photoelectronic devices. It is also observed that under high pressure, the AFM tip/monolayer WSe2/metal substrate junction transitions from Schottky to Ohmic contact, attributed to significant charge injection from the substrate to the WSe2. These findings are significant for designing efficient metal/semiconductor contact in thin and flexible PMOS (p‐type Metal–Oxide–Semiconductor) devices. [ABSTRACT FROM AUTHOR]

Double perovskites present promising opportunities for harnessing energy from both sunlight and wasted heat. In this study, we conducted a comprehensive theoretical analysis to evaluate the mechanical, electronic, optical, and transport properties of K2LiTlX6 (X = Cl, Br, I) employing the WEIN2K code. The optimized FCC unit cell's lattice parameters exhibited an increase from 10.34 to 11.98Å when substituting Cl with Br/I. To ascertain thermodynamic and structural stability, we computed the enthalpy of formation (-2.64 to -1.89 eV) and the tolerance factor (0.97 − 0.93). The results provide evidence for the thermodynamic and structural stability of the compounds. Mechanical parameter calculations, comprising bulk, Young, and shear moduli, along with Poisson's ratio in three dimensions, reveal their anisotropic nature, with greater significance observed in K2LiTlBr6 and K2LiTlI6. Moreover, the numerical values of Poisson and Pugh ratios indicated their ductile characteristics. The materials also exhibit noteworthy properties such as hardness, ultra-low lattice thermal conductivities, and greater melting and Debye temperatures, enhancing their potential applications. The direct bandgap values underwent a transformation from the visible to the infrared region (2.57 − 0.14 eV) as the halogen size increased. Using the BoltzTraP code, we calculated temperature-dependent thermodynamic parameters, showing high electrical conductivity related to thermal conductivity. The combination of a higher Seebeck coefficient and ZT highlighted the appropriateness of these compounds for future energy harvesting applications. [ABSTRACT FROM AUTHOR]

Despite extensive research on utilizing plasmonic hot carriers to advance photovoltaics and photocatalysts, achieving high hot‐carrier flux remains challenging due to their rapid relaxation. Recent studies have shown that combining plasmonic metals with perovskites improves hot‐electron flow, due to the slow hot‐electron relaxation in perovskites. Additionally, perovskites offer the advantage of facile bandgap tuning through composition changes. Herein, the influence of tuning the perovskite bandgap on the lifetime and flow of hot electrons in a perovskite/plasmonic Au/TiO2 nanodiode is explored. The findings reveal that perovskites with wider bandgaps exhibit improved hot‐electron lifetime and flow, attributed to the modified hot‐electron energy favoring a slower energy loss rate, as verified by ultrafast transient absorption spectroscopic analysis. It is believed that the results successfully demonstrate the integration of engineered hot‐carrier physics into device functions, providing valuable guidance for the design of optimized hot‐carrier‐based devices in the future. [ABSTRACT FROM AUTHOR]

Mechanical metamaterials are highly versatile structures capable of achieving unconventional mechanical properties. Of particular interest are mechanical metamaterials with the ability to tune bandgaps, offering potential applications in vibration control tailored to specific requirements. In this study, a new type of metamaterial is introduced to exhibit a distinctive two-step deformation mode under compressive displacement. Through a combination of numerical simulation and experimental verification, the band structure and vibration characteristics of the novel metamaterial in different stable states are thoroughly examined under compressive displacement. The results demonstrate that, in comparison to the initial structure, the novel mechanical metamaterial effectively addresses the issue of a significant reduction in plateau stress relative to buckling stress following buckling in the second deformation stage. The novel structure showcases notable controllable deformation capabilities, yielding distinct band structures in various stable states, and facilitating bandgap tuning. Furthermore, the study explores the influence of geometrical parameters and stable state transitions on bandgap evolution, supported by frequency response analyses and experimental validation. This research offers a fresh perspective on the utilization of Multistable Multi-Step Deformation Metamaterial (MMDM) for energy absorption and vibration damping applications. [ABSTRACT FROM AUTHOR]

Yttrium orthovanadate (YVO 4), a wide-bandgap photocatalyst was tuned into a visible responsive material by anchoring an organic framework on the surface of YVO 4 nanoparticles using polyethyleneimine (PEI). The surface organic framework was identified as the decomposed PEI derivatives with the carbonyl and carboxylic acid functional groups by the FTIR and XPS analyses. The top of the valence band (VB) was raised and the bottom of the conduction band was moved down; hence, the band gap of YVO 4 was reduced to absorb the light in the visible region for all three synthesized samples, which was confirmed by DRS UV–Vis analysis. The functional groups facilitated more water molecules on the YVO 4 surface via hydrogen bonding; hence, the YVO 4 surface acquired superhydrophilicity. Among the three YI, YII, and YIII samples synthesized with three different calcination temperatures of 80, 260 and 400 °C respectively, YII showed many advantageous photocatalytic properties. The optimum loading of organic compounds obtained on YII surface at 260 °C, which improved the surface area, visible light absorption, hydrophilicity, and exciton's life. Hence, YII showed a better performance of 3.75 mmol h−1g−1 cat H 2 production than YI and YII. This work interestingly revealed the influence of calcination temperature on surface functionalization and the performance of catalytic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Tuning electrical properties of 2D materials through mechanical strain has predominantly focused on n‐type 2D materials like MoS2 and WS2, while p‐type 2D materials such as WSe2 remain relatively unexplored. Here, the impact of controlled mechanical strain on the electron transport characteristics of both mono and bi‐layer WSe2 is studied. Through coupling atomic force microscopy (AFM) nanoindentation techniques and conductive AFM, the ability to finely tune the electronic band structure of WSe2 is demonstrated. The research offers valuable mechanistic insights into understanding how WSe2's electronic properties respond to mechanical strain, a critical prerequisite for the development of flexible photoelectronic devices. It is also observed that under high pressure, the AFM tip/monolayer WSe2/metal substrate junction transitions from Schottky to Ohmic contact, attributed to significant charge injection from the substrate to the WSe2. These findings are significant for designing efficient metal/semiconductor contact in thin and flexible PMOS (p‐type Metal–Oxide–Semiconductor) devices.

The suitability of halide-based double perovskites for implementation in infrared detectors and thermoelectric devices arises from their inherent environmental stability, non-toxic nature, and demonstrable performance. In the present investigation, our focus centers on an exploration of the structural stability and mechanical attributes intrinsic in Na2CuInY6 (Y = Cl, Br, I) within its cubic phase utilizing DFT. The structural and thermodynamic stability is investigated by computation of tolerance factor and enthalpy of formation. Our methodology encompasses comprehensive calculations of elastic constants based on Born stability criteria that help to understand the mechanical behavior and ductile nature of these compositions. Notably, our scrutiny of the electronic band structure reveals the presence of a direct semiconducting bandgap ranging between 1.30 and 0.36 eV. This distinctive feature holds a pivotal role in facilitating optoelectronic applications because of its pronounced role in absorption within the infrared spectrum. Remarkably, our investigation into the dielectric constant allows us to pinpoint the region of maximal light absorption within the visible spectrum. Lastly, using the BoltzTraP package, we computed the thermoelectric properties of the material and noticed an almost constant value of ZT in the wide range of temperatures highlighting the large range of workability of these compositions for thermoelectric device applications. [ABSTRACT FROM AUTHOR]

Flexible regulation of bandgap of perovskite nanocrystals (PNCs) is fundamentally critical for desirable optoelectronic functions and applications. Here, regulating chemical composition and emission wavelength of PNCs in glass by a simple heat‐treatment process are reported, which is established to rely on the thermal‐trigger phase separation and ion exchange. The first principle calculations are overall performed to reveal the mechanism of bandgap engineering and optimization of emission performance. The PNCs exhibit excellent stability against thermal, ultraviolet irradiation, and organic molecules. The bandgap of PNCs in the heat‐treated glass can also be re‐modulated by ultrafast laser irradiation. Ultrafast laser direct writing of multi‐color patterns and holographic dynamic displays are achieved, which hold great potential in the application of encryption‐decryption and emissive devices. [ABSTRACT FROM AUTHOR]

Chalcogenide perovskites have been proposed as one of the most promising candidates for solar cells due to their suitable bandgap, nontoxicity, and environmental stability. As a typically distorted perovskite, although BaHfS 3 possesses extraordinarily strong light absorption near the band edge, the slightly large bandgap of ∼2.1 eV has limited its applications in photoelectronic. In this work, the Ba(Hf 1−x Ti x)S 3 (0 ≤ x ≤ 0.05) perovskites with good crystallinity were first successfully synthesized and exhibited a reduced bandgap from 2.01 to ∼1.4 eV. Moreover, it is striking that the bandgap sharply decreases to 1.52eV (24 % compared to undoped compound) with only 1 atom % Ti-alloying concentration. The Density functional theory calculation shows that the contribution of Ti near the conduction band minimum (CBM) increases through the partial substitution of Ti for Hf. It is also demonstrated that the significant decrease in the bandgap is due to the downshift of the CBM caused by Ti–S antibonding coupling accordingly. This study provides a promising Ti-substituted BaHfS 3 material with excellent ambient and thermal stability, which can promote the use of chalcogenide perovskites in photovoltaics. [ABSTRACT FROM AUTHOR]

Nano-polycrystalline thin films of CuIn1-xAlxSe2 (CIAS) chalcopyrite material are re-grown on annealing the 700 nm thick Cu/In/Al/Se stack at temperatures ranging from 523 to 623 K. The stack is obtained at room temperature by sequentially evaporated layer deposition (SELD) technique. The grown films show a tetragonal crystal system of CIAS having unit cell parameters a; b = 5.781(5) Å, c = 11.593 (7) Å, with cell volume (V) = 387.523(4) Å3. The micrographs of the films show grains of spherical and cylindrical shapes. Raman spectra of the layers indicate A1 mode at 180.72(7) cm−1, which confirms the CIAS phase. The thin film's energy dispersive X-ray analysis (EDAX) establishes CuIn0.63Al0.37Se2 stoichiometry at 523 K. The direct allowed bandgap (Eg) value varies between 1.35 and 1.50 eV with a change in TA from 523 to 623 K; the values are near the optimum PV cell. The grown thin film samples exhibit absorption coefficient (α) ≥ 1 × 105 cm−1. The solar cell structure of FTO/p-CIAS/n-CdS/In exhibits a photovoltaic (PV) response.

The bandgap tuning potential offered by negative-stiffness lattice structures, characterized by their unique mechanical properties, represents a promising and burgeoning field. The potential of large deformations in lattice structures to transition between stable configurations is explored in this study. This transformation offers a novel method for modifying the frequency range of elastic wave attenuation, simultaneously absorbing energy and effectively generating diverse bandgap ranges. In this paper, an enhanced lattice structure is introduced, building upon the foundation of the normal negative-stiffness lattice structures. The research examined the behavior of the suggested negative-stiffness lattice structures when subjected to uniaxial compression. This included analyzing the dispersion spectra and bandgaps across different states of deformation. It also delved into the effects of geometric parameter changes on bandgap properties. Furthermore, the findings highlight that the normal negative-stiffness lattice structure demonstrates restricted capabilities in attenuating vibrations. In contrast, notable performance improvements are displayed by the improved negative-stiffness lattice structure, featuring distinct energy band structures and variable bandgap ranges in response to differing deformation states. This highlights the feasibility of bandgap tuning through the deformation of negatively stiffened structures. Finally, the overall metamaterial structure is simulated using a unit cell finite element dynamic model, and its vibration transmission properties and frequency response patterns are analyzed. A fresh perspective on the research and design of negative-stiffness lattice structures, particularly focusing on their bandgap tuning capabilities, is offered in this study. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of co-doped mesoporous nanocomposites consisting of zinc oxide (ZnO) and multi-walled carbon nanotubes (MWCNT) have been conducted. The synthesis has been carried out using a microwave-assisted hydrothermal approach. The confirmation of the formation of nanocomposites exhibiting a mesoporous morphology has been established through the utilization of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As per the energy dispersive X-ray (EDX) analysis, the synthesized samples contain nitrogen (N), carbon (C), silver (Ag), and iron (Fe) elements. The Brunauer-Emmett-Teller (BET) data analysis depicts class 4 hysteresis with 3.69 nm pore diameter and 21.52 m2/g surface area. The impact of co-doping nitrogen, silver, and iron on the reduction in energy band gap (3.2 to 2.6 eV) and electron-hole recombination has been illustrated using photoluminescence and UV-Vis spectroscopy. Furthermore, co-doped ZnO/MWCNT nanocomposites exhibit improved photocatalytic performance, with 94% and 98% degradation of congo red and methylene blue dyes, respectively. [ABSTRACT FROM AUTHOR]

The introduction of the 2D materials in recent years has resulted in an emerging type of the constructed structures called van der Waals heterostructures (vdWHs) that take advantage of the 2D materials in forming atomically thin components and devices. The vdWHs are constructed by the stacking of 2D materials by van der Waals interactions or edge covalent boning. The electron orbitals of the 2D layers in vdWHs extend to each other and influence the electronic band structures of the constituent layers. The tunable optical response over a wide range of the wavelengths (NIR to visible) can be obtained by assembling vdWHs through combining of the monolayers. By application of 2D layers in vdWHs, p-n heterojunctions without lattice mismatch can be formed. The photodiodes based on the van der Waals interactions could be considered as promising candidates for future optoelectronic devices. Furthermore, on-chip quantum optoelectronics can move to the next generation by using 2D materials in vdWHs. In this review, the vdWHs are introduced and their properties and applications in light-emitting diodes (LEDs) have been discussed. The vdWHs allow bandgap engineering, and hence, LEDs working in a range of the wavelengths can be realized. The applications of vdWHs in forming atomically thin components in optoelectronic devices and LEDs have been addressed.

Thin films of nanocrystalline selenium (Se) of different thicknesses were grown on annealing from 323 to 398 K. The crystallinity of the layers increased with annealing temperatures (TA). The temperature thickness correlations were established. The layers exhibited spherical-shaped particles at higher annealing temperatures. The grown layers possess hexagonal crystal system with space group P3121(152); it shows prominent planes along the a-axis. The bandgap (Eg) decreases from 2.18 to 1.94 eV, 2.12 to 1.82 eV, and 2.13 to 1.84 eV with changes in TA of 700, 270, and 150 nm thick layers, respectively. The high absorption coefficient (α) values ∼ 1 × 105 cm−1 observed in all films makes it suitable as an absorber layer in a solar cell structure and an optical sensor. The FTO/p-Se/n-CdS/In heterojunction diodes provide zero-bias barrier height (фbo) of 0.788(7) eV. The open circuit voltage (Voc) of FTO/p-Se (150 nm)/n-CdS(200 nm)/In a photovoltaic cell was observed to be 55 mV.

Highlights The CuaAgm1Bim2In/CuI bilayer films are prepared simultaneously in situ by a one-step low-temperature gas-solid phase diffusion induced elemental reaction without spin coating. A new type of CuaAgm1Bim2In photovoltaic material was originally designed to reduce the bandgap of this class of materials from 2.06 to 1.78 eV by breaking the restriction of double perovskite structure with a ratio of Ag:Bi = 1:1. The power conversion efficiency (PCE) of solar cell with a structure of FTO/TiO2/CuaAgm1Bim2In/CuI/carbon reached 2.76%, which is the highest PCE for CuaAgm1Bim2In absorbers.

The introduction of 2D materials in recent years has resulted in an emerging type of constructed structure called van der Waals heterostructures (vdseWHs) that take advantage of the 2D materials in forming atomically thin components and devices. The vdWHs are constructed by the stacking of 2D materials by van der Waals interactions or edge covalent boning. The electron orbitals of the 2D layers in vdWHs extend to each other and influence the electronic band structures of the constituent layers. The tunable optical response over a wide range of wavelengths (NIR to visible) can be obtained by assembling vdWHs by combining the monolayers. By application of 2D layers in vdWHs, p-n heterojunctions without lattice mismatch can be formed. The photodiodes based on the van der Waals interactions could be considered promising candidates for future optoelectronic devices. Furthermore, on-chip quantum optoelectronics can move to the next generation by using 2D materials in vdWHs. In this review, the vdWHs are introduced and their properties and applications in light-emitting diodes (LEDs) have been discussed. The vdWHs allow bandgap engineering, and hence, LEDs working in a range of wavelengths can be realized. The applications of vdWHs in forming atomically thin components in optoelectronic devices and LEDs have been addressed. [ABSTRACT FROM AUTHOR]

Chemical engineering in lead halide perovskite nanocrystals (PNCs) has garnered significant attention for tailoring optoelectronic properties, such as bandgap, quantum yield (QY), and stability. Here, pure blue emissive PNCs in glass by using ultrafast laser are reported. The emission wavelength is tuned in the range from 461 to 520 nm by engineering the chemical composition in the B‐site Cd/Pb mix‐cation system. The photoluminescence (PL) QY of CsCdxPb1−xBr3 PNCs reaches 13.4% for the pure blue emission at 467 nm, which is twice that of CsPbBryCl3−y PNCs. The pure blue emissive PNCs exhibit remarkable stability when exposed to ultraviolet (UV) radiation, heat, and ethanol solvents. The ultrafast laser print patterns can be encrypted and decrypted for information, which shows great potential for crucial information security applications. These results imply that B‐site engineering for lead halide PNCs embedded in glass is effective to tailor the PL spectra and increase the PL QY. The pure blue emissive PNCs hold great potential in the applications of blue and full‐color emissive devices. [ABSTRACT FROM AUTHOR]

Perovskite silicon tandem solar cells can overcome the efficiency limit of silicon single‐junction solar cells. In two‐terminal perovskite silicon tandem solar cells, current matching of subcells is an important requirement. Herein, a current‐matched tandem solar cell using a planar front/ rear side‐textured silicon heterojunction bottom solar cell with a p–i–n perovskite top solar cell that yields a high certified short‐circuit current density of 19.6 mA cm−2 is reported. Measures taken to improve the device are guided by optical simulation and a derived optical roadmap toward maximized tandem current density. To realize current matching of the two subcells, variation of the perovskite bandgap from ≈1.68 to 1.64 eV and thickness is investigated. Spectrometric characterization, in which current–voltage curves of tandem devices are recorded at systematically varied spectral irradiance conditions, is applied to determine the current matching point. In addition, remaining device limitations such as nonradiative recombination at the perovskite's interfaces are analyzed. Replacing the hole transport layer PTAA by 2PACz results in an overall certified power conversion efficiency of up to 26.8%. Precise simulation based on the device structure is essential as it provides efficient paths toward improving the device efficiency. [ABSTRACT FROM AUTHOR]

Highlights: The CuaAgm1Bim2In/CuI bilayer films are prepared simultaneously in situ by a one-step low-temperature gas-solid phase diffusion induced elemental reaction without spin coating. A new type of CuaAgm1Bim2In photovoltaic material was originally designed to reduce the bandgap of this class of materials from 2.06 to 1.78 eV by breaking the restriction of double perovskite structure with a ratio of Ag:Bi = 1:1. The power conversion efficiency (PCE) of solar cell with a structure of FTO/TiO2/CuaAgm1Bim2In/CuI/carbon reached 2.76%, which is the highest PCE for CuaAgm1Bim2In absorbers. Lead-free inorganic copper-silver-bismuth-halide materials have attracted more and more attention due to their environmental friendliness, high element abundance, and low cost. Here, we developed a strategy of one-step gas–solid-phase diffusion-induced reaction to fabricate a series of bandgap-tunable CuaAgm1Bim2In/CuI bilayer films due to the atomic diffusion effect for the first time. By designing and regulating the sputtered Cu/Ag/Bi metal film thickness, the bandgap of CuaAgm1Bim2In could be reduced from 2.06 to 1.78 eV. Solar cells with the structure of FTO/TiO2/CuaAgm1Bim2In/CuI/carbon were constructed, yielding a champion power conversion efficiency of 2.76%, which is the highest reported for this class of materials owing to the bandgap reduction and the peculiar bilayer structure. The current work provides a practical path for developing the next generation of efficient, stable, and environmentally friendly photovoltaic materials. [ABSTRACT FROM AUTHOR]

Bandgap tuning is a key approach to optimizing materials for advanced technologies, enabling the development of more efficient and specialized devices. In this study, we demonstrate the tunability of the bandgap of CuCrO 2 from 2.38 to 4.37 eV via single cation-doping with Ni and Zn, and multi-cation doping with Ni-Zn and Ni-Zn-Mg. XRD analysis reveals structural changes due to lattice distortions by cationic substitution, while FESEM shows the impact of doping on particle size, surface morphology, and crystallinity. The lamellar structure observed with multi-cation doping in FESEM investigations indicates increased structural disorder and defects, causing tailing above the valence band and below the conduction band, significantly reducing the bandgap. The effect of Zn-Ni doping on the lattice is reversed with Mg 2 + insertion due to p-p orbital interactions between Mg 2 + -O, replacing the d-p interaction in the Cr3＋-O bond, as confirmed by optical studies. UV–Vis and photoluminescence analyses reveal significant shifts in bandgaps and emission spectra, with Ni doping yielding a bandgap of 3.97 eV, Zn doping 3.16 eV, Zn-Ni doping expanding it to 4.37 eV, and Zn-Ni-Mg doping reducing it to 2.38 eV. The dopants also affect emission characteristics, including band edge and deep-level emissions. This study provides valuable insights into the relationship between cationic doping and material properties, guiding the design of CuCrO 2 -based materials with tailored functionalities. [ABSTRACT FROM AUTHOR]

Thin silver oxide graphene (Ag 2 O@G) nanocomposite films were synthesized via facile spray pyrolysis and integrated into heterojunction architectures with silicon substrate. Structural characterization confirmed the successful anchoring of crystalline Ag 2 O nanoparticles uniformly over graphene layers with strong interfacial coupling. Optical analysis showed synergistic tuning of the band structure by hybridization, which improves light absorption. Electrical measurements showed rectification behavior of the diode and an increase in photocurrent up to milliamperes under illumination. A response time of 350 ms, a recovery time of 400 ms, stability over repeated cycles and exceptional values such as 0.39 A/W responsivity, 88 % external quantum efficiency and 4×1011 Jones detectivity at 600 nm were achieved. The nanocomposite heterojunctions utilize the superior charge mobility of graphene with the bandgap tuning of Ag 2 O, enabling efficient light harvesting, photogeneration, and ambipolar charge separation and transport across the multifunctional interface. Customized Ag 2 O@G heterostructures represent a promising material platform to drive advances in high performance photodetectors, image sensors, night vision devices and photovoltaics through the engineering of morphology, crystallinity and interfaces. • Uniform Ag 2 O nanoparticle decoration on graphene with strong interfacial coupling. • Ag 2 O@G nanocomposites integrated into Si heterojunctions via scalable spray pyrolysis. • Synergistic light absorption, charge transport tuned by hybridization and interfaces. • Good photodetector metrics: 0.39 A/W responsivity, 88 % EQE, 1011 Jones detectivity. • Bridging nanocarbon, metal oxides, semiconductors for transformative optoelectronics. [ABSTRACT FROM AUTHOR]

Transition Metal Chalcogenide Perovskites (TMCP) have been in the spotlight due to their exceptional optoelectronic properties. CaZrS 3 is one among them with an experimental bandgap of 1.90 eV. If its bandgap is tuned to lower values, it can be employed in additional photovoltaic applications, such as solar cell absorbers. In this work, the transition metal element Zr in CaZrS 3 is substituted with Ti atoms in different proportions and the optoelectronic properties are investigated using Density Functional Theory (DFT). The optoelectronic calculations are all done using the DFT+U method including the spin–orbit coupling. With substitutional alloying, we successfully tuned the energy gap from 1.91 eV to 1.18 eV and the photovoltaic properties were also observed to be modified. For the substituted CaZr 1 − x Ti x S 3 samples, large birefringence is observed. This indicates enhancement in optical anisotropy via substitutional alloying which is significant in both linear and nonlinear optoelectronic applications like polarizers, wave plates etc. [Display omitted] • Bandgap tuning with substitutional alloying. • Density Functional Theory based theoretical study. • Tailoring photovoltaic properties of CaZrS 3 with Ti alloying. • Comparison of optical anisotropy with birefringence calculation. [ABSTRACT FROM AUTHOR]

In the present work, pristine and transition metal (TM) (W, Ag, Zn)-doped SnO2 nanocrystals using a facile sol–gel approach were synthesized. The grown products were anchored on graphene oxide (GO) sheets via a simple ultrasonication technique to fabricate binary nanocomposites. The structural, optical, and morphological properties of as-synthesized samples were studied by XRD, FTIR, Raman, EDX, UV–Visible, PL, and FE-SEM. The charge transferability of graphene oxide-based samples was investigated by EIS. The XRD exhibited the TM doping in SnO2 and the development of GO-based nanocomposite. FTIR data evidenced the existence of the metal–oxygen bonds. Raman spectra presented the optical phonon modes of SnO2 and the existence of oxygen vacancy defects. FE-SEM images demonstrated the anchoring of particles on the GO sheet, and EDX further approved the existence of desired dopants. The integration of SnO2 with TM doping remarkably reduced optical bandgap (3.65–3.10 eV), which was further decreased (3.10–2.99 eV) by making composite with GO. The photodegradation results exhibited that GO-based nanocomposites have the higher potential to degrade synthetic dyes (methyl red (MR), and methyl orange (MO) and SnZnO2/GO have shown superb photocatalytic performance after 80-min sunlight illumination (99.9% MR and 95.0% MO dyes) with the higher rate constant and superior stability up to 6th cycle against MR dye. The grown samples were tested for bacterial disinfection, and SnZnO2/GO sample showed a higher zone of inhibition towards S. aureus and K. pneumoniae bacteria strains. The greater charge transfer rate and lower recombination of charge carriers in GO-based composites were also observed by EIS and PL analysis. Moreover, the present article ascribed that the photocatalytic and antibacterial properties of bare SnO2 could be improved by TM doping and fabricating their composite with GO. [ABSTRACT FROM AUTHOR]

Engineering the chemical composition of metal‐halide perovskites via halide mixing allows a facile bandgap modulation but renders perovskite materials prone to photoinduced halide segregation. Triple‐halide alloys containing Cl, I, and Br were recently reported as a means to stabilize CsyFA1–yPb(BrxI1–x)3 perovskite under illumination. Herein, these triple‐halide alloys are found to be intrinsically less stable with respect to the reference I‐Br in ambient conditions. By exploiting the influence of low‐molecular‐weight organic gelators on the crystallization of the perovskite material, a triple‐halide alloy with improved moisture tolerance and thermal stability at temperatures as high as 120 °C is demonstrated. The hydroxyl‐terminated organic gelators are found to aggregate into nanoscale fibers and promote the gelation of the solvent inducing the formation of a 3D network, positively interfering with perovskite solidification. The addition of a tiny amount of organic gelators imparts a more compact morphology, higher crystallinity, and compositional stability to the resulting triple‐halide polycrystalline films, making them more robust over time without compromising the photovoltaic performance. Overall, this approach offers a solution toward fabrication of active perovskite materials with higher energy gap and improved stability, making these triple‐halide alloys truly exploitable in solar cells. [ABSTRACT FROM AUTHOR]

Tungsten trioxide (WO3) is mainly studied as an electrochromic material and received attention due to N-type oxide-based semiconductors. The magnetic, structural, and optical behavior of pristine WO3 and gadolinium (Gd)-doped WO3 are being investigated using density functional theory. For exchange-correlation potential energy, generalized gradient approximation (GGA+U) is used in our calculations, where U is the Hubbard potential. The estimated bandgap of pure WO3 is 2.5 eV. After the doping of Gd, some states cross the Fermi level, and WO3 acts as a degenerate semiconductor with a 2 eV bandgap. Spin-polarized calculations show that the system is antiferromagnetic in its ground state. The WO3 material is a semiconductor, as there is a bandgap of 2.5 eV between the valence and conduction bands. The Gd-doped WO3's band structure shows few states across the Fermi level, which means that the material is metal or semimetal. After the doping of Gd, WO3 becomes the degenerate semiconductor with a bandgap of 2 eV. The energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) configurations is negative, so the Gd-doped WO3 system is AFM. The pure WO3 is nonmagnetic, where the magnetic moment in the system after doping Gd is 9.5599575 μB. [ABSTRACT FROM AUTHOR]

In hybrid perovskite photovoltaics (hPPV) highest reported efficiency is ∼25.2%. However, stability and toxicity are major concern towards commercialization. To improve stability, various approaches were made by research communities. Utilizing inorganic perovskite photoactive materials is one such approach to improve stability. Toxic element 'Pb' can be substituted with suitable non-toxic elements such as 'Sn' without sacrificing efficiency and stability. In CsPbI 3 , replacing Sn in place of Pb results in the PCE of ∼13%. However, efficiency of this PV is lagging 12% as compared with hybrid perovskite PV. This difference should be overcome to compete with hPPV. To improve the efficiency of inorganic PPV various experimental strategies were adopted. In this study, SCAPS simulation was carried out on FTO/TiO 2 /CsSnI 3 /spiro-OMeTAD/Au by altering E g , energetic position of conduction and valence band, defect density, and thickness of semiconductor. Obtained results were analyzed and reported in this work. [ABSTRACT FROM AUTHOR]

We systematically analyze triple-cation perovskite solar cells for indoor applications. A large number of devices with different bandgaps from 1.6 to 1.77 eV were fabricated, and their performance under 1-sun AM1.5 and indoor white light emitting diode (LED) light was compared. We find that the trends agree well with the detailed balance limit; however, the devices near the optimal bandgap (1.77 eV) perform worse due to the lower perovskite quality. Instead, we achieve the highest power conversion efficiency (PCE) of 34.0% under 870 lx with 1.67 eV and Al 2 O 3 passivation. The perovskite with a bandgap of 1.71 eV is not far behind, with a high V OC of 1.02 V. Measurements under different white LED color temperatures confirm that the highest PCE is achieved under the warmest colors. All measurements were carried out in a dedicated indoor setup that ensures the diffuse light typical of indoor environments and allows both short- and long-term measurements. In the best case, we observe no degradation during the 33-day test under simulated office conditions with regular switching on and off of the light and a T 80 of 30 days under continuous illumination. The results were obtained from multiple batches, which corroborates our findings and gives them statistical relevance.

Two-dimensional (2D) lead halide perovskites have garnered increasing interest due to their high photoluminescence quantum yields and tunable luminescence characters, making them excellent materials in light-emitting, especially for white-light emission. In contrast to their 3D analogues, they are formed by inserting large organic cations between the anionic layers of lead halide octahedra. Herein, we designed and prepared AVA2PbClxBr4-x (x = 0, 1, 2, 3, 4) alloy perovskites, in which AVA (5-aminovaleric acid) was used as an organic cation to separate the layers of chlorine-substituted lead bromide 2D perovskite, in order to identify the role of Cl substitution in tuning the bandgap and luminescence characters of the 2D AVA2PbBr4 perovskite. X-ray diffraction measurements revealed achievement of single-phase thin films of AVA2PbClxBr4-x perovskites with a (001) orientation. With increasing Cl/Br ratio from 0 to 1, the lattice constant c was found to decrease from 1.672 nm to 1.597 nm following c(x) = 1.674 – 0.076x, while the bandgap increased from 3.11 eV to 3.76 eV as approximated with Eg(x) = 3.08 + 0.62x. Correspondingly, the alloy luminescence character evolved from narrow-band blue-violet to broadband white-light emission, which was attributed to transformation from free-exciton to self-trapped-exciton emission with increasing octahedral distortion caused by Cl substitution. Based on an alloy system with continuously varying content designed for the first time, the work highlighted the role of Cl incorporation in changing the crystal lattice structure, and tuning bandgap as well as the light emission characters in 2D lead halide perovskites.

Polymers have gained attraction at the industrial level owing to their elastic and lightweight nature, as well as their astonishing mechanical and electrical applications. Their scope is limited due to their organic nature, which eventually leads to the degradation of their properties. The aim of this work was to produce polymer composites with finely dispersed metal oxide nanofillers and carbon nanotubes (CNTs) for the investigation of their charge-storage applications. This work reports the preparation of different polymeric composites with varying concentrations of metal oxide (MO) nanofillers and single-walled carbon nanotubes (SWCNTs). The successful synthesis of nanofillers (i.e., NiO and CuO) was carried out via the sonication and precipitation methods, respectively. After, the smooth and uniform polymeric composite thin films were prepared via the solution-casting methodology. Spectroscopy and diffraction techniques were used for the preliminary characterization. Scanning electron microscopy was used to check the dispersion of carbon nanotubes (CNTs) and MOs in the polymer matrix. The addition of nanofillers and carbon nanotubes (CNTs) tuned the bandgap, reduced the strain, and enhanced the elastic limit of the polymer. The addition of CNT enhanced the mechanical strength of the composite; however, it increased the conductivity, which was tuned by using metal oxides. By increasing the concentration of NiO and CuO from 2% to 6% bandgap of PVA, which is 5–6 eV reduced to 4.41 and 4.34 eV, Young's moduli of up to 59 and 57.7 MPa, respectively, were achieved. Moreover, improved dielectric properties were achieved, which shows that the addition of metal oxide enhances the dielectric behavior of the material. [ABSTRACT FROM AUTHOR]

A comprehensive device performance optimization of perovskite solar cells (PSCs) having the device configurations FTO/IGZO/CsSn0.5Ge0.5I3/CuO/Au, FTO/IGZO/Cs4CuSb2Cl12/CuO/Au, and FTO/IGZO/Cs3Bi2I9/CuO/Au containing the single, double, and ternary perovskites CsSn0.5Ge0.5I3, Cs4CuSb2Cl12, and Cs3Bi2I9, respectively, is done utilizing the SCAPS 1D tool. The bandgap tuning of the perovskite layers and the work function optimization of the rear‐contact metals for the chosen device designs provide an enhanced power conversion efficiency of 23.15%, 17.39%, and 9.75% for the solar cell architecture with the light‐captivating layers CsSn0.5Ge0.5I3, Cs4CuSb2Cl12, and Cs3Bi2I9, respectively. Herein, it is identified the variation of electron affinity of the perovskite layer for the aforementioned device configurations does not produce any significant enhancement in the output parameters of the simulated configurations. [ABSTRACT FROM AUTHOR]

Successful integration of perovskite cell with silicon cell to form a tandem solar device has shown tremendous potential for outperforming the state-of-the-art single junction silicon devices. This tandem approach has enabled high efficiencies up to 29% within a short period of time and one can find sufficient work and various strategies being applied to enhance the efficiency in these devices. At this point in time, a compilation of all these studies, with a critical review and perspectives is extremely relevant and essential. With this motivation the present review has been brought out, with all achievements attained so far by optimizing various components namely the electron/hole transport layer and absorber layer, functional layers in bottom cell, transparent contacts, deposition techniques and the innovative light management tactics used. The review also outlines the solutions proposed by various researchers to overcome the challenges that restrict the efficiency of tandem strategy in three distinct configurations, namely, monolithic (2T), four terminal (4T) and three terminal (3T) configurations. Finally, the perspectives provide real insights into choosing suitable materials, techniques and methods and achieve efficiencies near and beyond Shockley Queisser limit, thus spiking high hopes that this device would be the dominant energy conversion device in future.

Tungsten trioxide (WO3) is mainly studied as an electrochromic material and received attention due to N-type oxide-based semiconductors. The magnetic, structural, and optical behavior of pristine WO3 and gadolinium (Gd)-doped WO3 are being investigated using density functional theory. For exchange-correlation potential energy, generalized gradient approximation (GGA+U) is used in our calculations, where U is the Hubbard potential. The estimated bandgap of pure WO3 is 2.5 eV. After the doping of Gd, some states cross the Fermi level, and WO3 acts as a degenerate semiconductor with a 2 eV bandgap. Spin-polarized calculations show that the system is antiferromagnetic in its ground state. The WO3 material is a semiconductor, as there is a bandgap of 2.5 eV between the valence and conduction bands. The Gd-doped WO3’s band structure shows few states across the Fermi level, which means that the material is metal or semimetal. After the doping of Gd, WO3 becomes the degenerate semiconductor with a bandgap of 2 eV. The energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) configurations is negative, so the Gd-doped WO3 system is AFM. The pure WO3 is nonmagnetic, where the magnetic moment in the system after doping Gd is 9.5599575 μB.

The antiperovskites based on metal halides have emerged as potential materials for advanced photovoltaic and electronic device applications. But the wide bandgap of non-toxic CsSnCl3 reduces its photovoltaic efficiency. Here, we report the change of electronic structure of CsSnCl3 at different pressure by using GGA-rPBE and GGA-PBEsol functionals and the GW method. We have shown that the prediction of electronic structure transition (semiconducting to metallic state) strongly depends on the exchange-correlation and the GW method gives the most reasonable values of the bandgap under pressure. The pressure increases the electronic density of states close to the Fermi level by pushing the valence electrons upward and thus, reduces the bandgap linearly. Afterward, we have also investigated the influence of pressure on absorption coefficient, and mechanical properties meticulously. Although the pressure shifts the absorption peak to lower photon energies, the absorption coefficient is slightly improved.

Novel glass-ceramic composites with optical bandgap tunability were synthesised. Zinc silicate powder (ZS) was mixed with multi-walled carbon nanotubes (MWCNTs) at various mass fractions (0, 1, 2, and 3 wt %), followed by argon sintering. X-ray diffraction (XRD) analysis revealed the structural change from an amorphous ZS phase to a crystalline willemite phase (Zn 2 SiO 4) by adding MWCNTs, and the largest crystallite size was obtained for ZS with 2.0 wt% MWCNTs. Although the agglomeration of ZS and MWCNTs was observed by field emission scanning electron microscopy (FESEM), there was no chemical interaction between ZS and MWCNTs as confirmed by Fourier transform infrared spectroscopy (FTIR). MWCNTs enhanced the crystallisation, which led to the green emission of Zn 2 SiO 4 blue-shifting from 572 nm to 557 nm. The narrowed optical bandgap of Zn 2 SiO 4 was attributed to the MWCNT-induced exciton localised between the valence band and conduction band of Zn 2 SiO 4. The bandgap tuning effect of MWCNTs potentially paved new ways to mass fabricate zinc silicate-based semiconductors with desirable optical bandgap energy E g , which significantly benefits the sensor and laser-related industry. [ABSTRACT FROM AUTHOR]

• The layer-gradient periodic pipe provides a feasible solution for bandgap tuning in limited space. • The layer-gradient periodic pipes can reduce the frequencies of higher-order bandgaps. • The coupling between layers makes the bandgaps of layer-gradient periodic pipes more complex. This paper presents a vibration control strategy that installs layer-gradient periodic pipes on general pipelines to suppress the transmission of bending vibration. Bandgap tuning can be achieved without changing the structural size. Initially, a composite cell is constructed based on the bandgap characteristics of ordinary periodic pipes, and a layer-gradient periodic pipe is innovatively designed. Secondly, the bending vibration model of the fluid-filled pipeline under external axial force is established using Hamilton's principle. Combining Bloch's theorem, the transfer matrix method is applied to derive the transfer formula for bending waves. The band structure of the layer-gradient periodic pipe is obtained by solving the eigenvalue equation. Subsequently, the frequency tuning advantages of the layer-gradient periodic pipes are demonstrated through a comparison with the conventional periodic pipes. The effectiveness of the proposed vibration control strategy is verified by finite element simulation. Finally, the effects of liquid filling, layer thickness ratio, number of layers, component ratio, and different material combinations on the bandgap characteristics are discussed. The results indicate that the layer-gradient periodic pipe can reduce the frequency of high-order bandgaps to a certain extent. This study can provide insights into the structural design, bandgap tuning, and engineering applications of periodic pipes in limited spaces. [ABSTRACT FROM AUTHOR]

Recently, hybrid perovskite (HP) materials due to their bandgap tuning properties have emerged as one of the alternatives for highly efficient hybrid perovskite solar cells (HPSCs). In this paper, the bandgap of MAPb 1−x Sn x I 3 was tuned from 1.55 to 1.25 eV by varying the Sn concentration. This article utilizes SCAPS-1D device simulation software to investigate the impact of bandgap tuning of the absorber layer on the device performance. We further investigated different design strategies and factors such as absorber layer thickness, defect density and defect energy level of the absorber layer, and doping density of the carrier selective layers. The best device performance was achieved for x = 0.9 in MAPb 1−x Sn x I 3 with the power conversion efficiency (PCE) of 30.66%, J sc = 35.02 mA/cm2, V oc = 1.058 V, and FF = 82.74%, under AM 1.5 G illumination by optimizing the device parameters. We have also considered the impact of interface defect density on the device performance. The investigation of this article reports a better device performance compared to the existing single-cell structure and it can play a vital role to aid the researchers in the selection of materials for designing high-efficiency solar cells. • Hybrid perovskite combines the advantages of both inorganic and organic perovskite. • It allows us to tune the bandgap to a value that is better suited for the light harvester. • Performance of the device has been increased with the incorporation of tin in place of lead. • Effect of several factors including absorber layer thickness has been investigated using SCAP-1D. • SCAP-1D gives us an opportunity to investigate the device's performance before fabricating it. [ABSTRACT FROM AUTHOR]

The structural characteristics and qualities of two-dimensional (2D) materials can be engineered and improved for use in practical applications by applying strain. In this study, the structural, electronic, and optical properties of 2D Y 2 CCl 2 MXene are investigated by density functional theory (DFT). Our results show that the transition of bandgap indirect–direct occur under 8 % tensile strain which is related to the electronic states around the Fermi level. Moreover, the phonon spectra indicate that 2D Y 2 CCl 2 can continue to be stable with +8 % strain. The optical properties are investigated under the biaxial strain. The results of the absorption spectrum show that 2D Y 2 CCl 2 has good absorption in the near-infrared, visible, and UV regions. Hence, this material may be used in solar cell applications. Our results indicate that the tunable electronic and optical properties of semiconducting Y 2 CCl 2 MXene make them a promising candidate for the future applications of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Carbon-Dots (C-Dots) have drawn much attention in recent years owing to their remarkable properties such as high biocompatibility, low toxicity, nano-scale size, and ease of modification with good tuneable photoluminescence performance. These unique properties have led C-Dots to become a promising platform for bioimaging, metal ion sensing and an antibacterial agent. C-Dots can be prepared using the top-down and bottom-up approaches, in which the latter method is commonly used for large scale and low-cost synthesis. C-Dots can be synthesized using sustainable raw materials or green biomass since it is environmentally friendly, in-expensive and most importantly, promotes the minimization of waste production. However, using biomass waste to produce high-quality C-Dots is still a matter of concern waiting for resolution, and this will be the main focus of this review. Fundamental understanding of C-Dots such as structure analysis, physical and chemical properties of C-Dots, various synthesis methodology and type of raw materials used are also discussed and correlated comprehensively. Additionally, factors affecting the bandgap of the C-Dots and the strategies to overcome these shortcomings are also covered. Moreover, formation mechanism of C-Dots focusing on the hydrothermal method, option and challenges to scale up the C-Dots production are explored. It is expected that the great potential of producing C-Dots from agricultural waste a key benefit in view of their versatility in a wide range of applications.

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The formation of an AlZnN alloy was investigated as a route to tune the bandgap of Zn3N2. A significant shift of the bandgap was observed in the deposited films, increasing from 1.4 eV for Zn3N2 to 2.8 eV for AlZnN alloys with an AlN fraction of × = 0.19. The refractive index followed a similar trend, approaching that of AlN. The charge carrier density of AlZnN samples was significantly reduced reaching values in the order of 1016 cm−3.

The family of two-dimensional (2D) transition-metal carbides and nitrides, known as MXenes, has attracted substantial attention in science and technology. The electronic structure, optical properties, and bandgap tuning under compressive and tensile strain (CTS) of 2D Sc2CF2 are investigated herein using density functional theory calculations. The results reveal that the bandgap of 2D Sc2CF2 can be tuned by applying CTS. The covalent bonding between the atoms become stronger under compressive strain. To investigate the optical properties, the absorption spectrum and percentage reflectivity of these structures along the x and z directions are calculated using the real and imaginary parts of the dielectric function. Upon applying 2%, 4%, and 6% compressive strain, the number of absorption peaks increases in the visible region along the x direction. These tunable electronic and optical properties of semiconducting 2D Sc2CF2 make it a candidate for the design of optoelectronic devices and in nanodevice applications. [ABSTRACT FROM AUTHOR]