Tunable Band Gap Research Articles

Catalyst-assisted growth of CsPbBr3 perovskite nanowires.

Halide perovskites (HPs), particularly at the nanoscale, attract attention due to their unique optical properties compared to other semiconductors. They exhibit bright emission, defect tolerance, and a broad tunable band gap. The ability to directly transport charge carriers along the HPs nanowires (NWs) has led to the development of methods for their synthesis. Most of these methods involve some version of an oriented attachment step with various modifications. In this study, we introduce CsPbBr3 nanowires produced via the solution-solid-solid (SSS) catalyst-assisted growth mechanism for the first time. We explored the kinetics of this process and examined the connection between the catalyst phase and its reactivity. We show how HP NWs grow with different SSS catalysts (i.e., Ag2S, Ag2Se, CuS) and discuss the required conditions for successful synthesis utilizing this mechanism. This method opens up a new avenue for producing HP NWs, which can be used to design and form new types of hybrid nanostructures.

Efficiency enhancement of WSe2/In2S3 solar cell by numerical modeling using SCAPS

Tungsten diselenide (WSe2), a transition metal dichalcogenide (TMDC) compound, is considered a promising material for application in thin film solar cells because of its high carrier transport, tunable band gap, and high absorption coefficient. In this work, solar cell structure comprising FTO/In2S3/WSe2 is modeled using one-dimensional solar cell capacitance simulator (SCAPS-1D) software where wide bandgap widely accessible In2S3 is used as a novel buffer layer instead of toxic CdS buffer layer for WSe2-based solar cell. The effect of thickness, doping concentrations, defect density, radiative recombination coefficient, and the electron and hole capture cross-section are analyzed and optimized. After optimizing the device, the effect of operating temperature, shunt and series resistance and back contact work function are also investigated. At an optimized WSe2 absorber layer thickness of 1.5 µm and acceptor density of 1017 cm−3, efficiency of 22.53%, fill factor of 84.98%, open circuit voltage of 1.096 V, and short circuit current density of 24.18 mA/cm2 was obtained. Additionally, a back surface field (BSF) layer comprising amorphous silicon (a-Si) of thickness 0.05 µm is introduced between the absorber layer and the back contact to lessen carrier recombination at the back surface. Therefore, the efficiency rises from 22.53% to 29.5% with a fill factor of 89.53%, open circuit voltage of 1.26 V, and short circuit current density of 26.23 mA/cm2. The simulation results suggest that WSe2-based thin-film solar cells can be designed and fabricated with high efficiency and cost advantage.

Enhanced Efficiency and Stability of Triple-Cation Perovskite Solar Cells through Engineering of the Cell Interface with Phenylethylammonium Thiocyanate.

It is reported that the tricationic mixed halide perovskite Csx(FAyMA1-y)1-xPb(IzBr1-z)3 (CsFAMA) possesses a stable crystal structure and outstanding bandgap tunability, rendering it one of the most competitive candidates for commercial perovskite solar cells (PSCs). Nevertheless, the numerous defects at the interface of the tricationic perovskite give rise to a significant constraint on the light capture performance of the device. Simultaneously, water molecules form intermediate compounds with the perovskite at the interface via hydrogen bonds, accelerating the degradation of the perovskite. This study reports the introduction of two-dimensional (2D) phenylethylthiocyanate (PEASCN) at the interface of three-dimensional (3D) perovskite. This approach significantly passivates the surface defects of the perovskite. Concurrently, due to the propensity of the organic ammonium cation PEA+ to interact with the FA+ base within the perovskite, SCN- is exposed outward to form a small-molecule hydrophobic layer. This method markedly reduces the loss of charge recombination and significantly enhances the device stability. The results indicate that the efficiency of the conventional device treated solely with PEASCN is as high as 23.94%. The unsealed device retains 85.12% of its initial efficiency after being placed in a conventional environment for 500 h. Furthermore, this surface passivation and hydrophobic strategy can be universally applicable to perovskite types with a high FA+ content.

A Mini‐Review: The Rise of Triple‐Junction Silicon‐Perovskite‐Perovskite Solar Cells

Recently, the multijunction (MJ) solarcells have gained interest and have a lot of promise going forward. As MJ solarcells with an increasing number of absorber layers can reduce the thermalization and the nonabsorption losses of the device, it has then been proposed to overcome the Shockley–Queisser (S–Q) maximum efficiency limit. The preparation of the metal halide perovskite using a solution processing method with tunable bandgaps has made them an ideal candidate to integrate with the silicon photovoltaic, forming MJ silicon‐perovskite (Si‐PVK) solar cells. Benefitting from these, 33.90% power conversion efficiency (PCE) has been realized for the Si‐PVK MJ solar cell, which is comparable to the S–Q maximum efficiency limit in the range of ≈1.10–≈1.30 eV. Furthermore, the PCE of Si‐PVK solar cells can potentially increase with increasing the number‐junction of perovskite device. Taking advantage of this, the research on the triple‐junction (TJ) silicon‐perovskite‐perovskite (Si‐PVK‐PVK) solar cells has gained attention, although it is still in an early stage of development. In this mini‐review, the working mechanism, the design principle, and the progress of TJ Si‐PVK‐PVK solar cells are discussed. Finally, future outlooks in this field are also provided.

Temperature-responsive metamaterials made of highly sensitive thermostat metal strips.

Temperature-responsive metamaterials have remarkable shape-morphing ability during thermal energy conversion. However, integrating the thermal shape programmability, wide-working temperature range, fast temperature response, and actuation into metamaterials remains challenging. Here, we introduce using thermostat metal strips to assemble metamaterials with desirable and balanced temperature-responsive properties, and we systematically investigate the thermal deformation performance. Achieving 70 to 80% of the designed strain requires only 5 seconds of heating. A thermal strain of around 30% is achieved for the assembled metamaterials, surpassing other bimetallic metamaterials by a magnitude of 100 to 200. The actuation capacity of thermostat metal strips exceeds 26 times their weight. Further, by leveraging the highly programmable thermal deformation, the tuneable bandgap range is 3847 to 40,000 hertz. These fully integrated mechanical performances in the multiphysics have great application potential, for example, as soft actuators and soft robots in intelligent structure systems, vibration isolation and noise reduction in hypersonic vehicles, and unique thermal deformation in precision instruments.

Nondestructive halide exchange via SN2-like mechanism for efficient blue perovskite light-emitting diodes

Blue perovskite light-emitting diodes (PeLEDs) still remain poorly developed due to the big challenge of achieving high-quality mixed-halide perovskites with wide optical bandgaps. Halide exchange is an effective scheme to tune the emission color of PeLEDs, while making perovskites susceptible to high defect density due to solvent erosion. Herein, we propose a versatile strategy for nondestructive in-situ halide exchange to obtain high-quality blue perovskites with low trap density and tunable bandgaps through long alkyl chain chloride incorporated chloroform post-treatment. In comparison with conventional halide exchange method, the ionic exchange mechanism of the present strategy is similar to a bimolecular nucleophilic substitution process, which simultaneously modulates perovskite bandgaps and inhibits new halogen vacancy generation. Consequently, efficient PeLEDs across blue spectral regions are obtained, exhibiting external quantum efficiencies of 23.6% (sky-blue emission at 488 nm), 20.9% (pure-blue emission at 478 nm), and 15.0% (deep-blue emission at 468 nm), respectively.

Technique for Creating 3D Ordered Colloidal Crystals with Hexagonal Close Packing and Uniform Thickness over a Large Area.

Traditional approaches to creating colloidal crystals do not simultaneously achieve uniform thickness, three-dimensional ordering, and large areas of defect-free hexagonal close-packed domains. Only the realization of all these conditions will allow the use of colloidal crystals as templates for fabricating inverse opals with a tunable photonic band gap. Therefore, we propose a novel approach for creating 3D colloidal crystals. It combines the use of the Langmuir-Blodgett (LB) process to form the first layer and sequential spin-coating processes to form all following layers. The original automated LB trough, equipped with a feedback control system for surface pressure control, allowed the formation of a close-packed monolayer across the entire area of a 76 mm substrate, obtaining a defect-free domain area of 3000 μm2. As a result of the developed spin-coating technique, bilayer and three-layer colloidal crystals based on polystyrene spheres (1.25 and 1.8 μm) were obtained. Three-dimensional HCP structure covered ≈96.5% of the substrate, and a defect-free domain area was obtained at least 1000 μm2. The high degree of 3D ordering was confirmed by the presence of stop bands in the transmission spectra at wavelengths corresponding to Bragg diffraction from parallel planes and a 2D array of spherical particles.

Effects of Substrate Temperature on Optical, Structural, and Surface Properties of Metal–Organic Vapor Phase Epitaxy-Grown MgZnO Films

MgZnO possesses a tunable bandgap and can be prepared at relatively low temperatures, making it suitable for developing optoelectronic devices. MgxZn1−xO (x~0.1) films were grown on sapphire by metal–organic vapor phase epitaxy under different substrate-growth temperatures Ts of 350–650 °C and studied by multiple characterization technologies like X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Raman scattering, extended X-ray absorption fine structure (EXAFS), and first-principle calculations. The effects of Ts on the optical, structural, and surface properties of the Mg0.1Zn0.9O films were studied penetratively. An XRD peak of nearly 35° was produced from Mg0.1Zn0.9O (0002) diffraction, while a weak peak of ~36.5° indicated MgO phase separation. SE measurements and analysis determined the energy bandgaps in the 3.29–3.91 eV range, obeying a monotonically decreasing law with increasing Ts. The theoretical bandgap of 3.347 eV, consistent with the SE-reported value, demonstrated the reliability of the SE measurement. Temperature-dependent UV-excitation Raman scattering revealed 1LO phonon splitting and temperature dependency. Zn-O and Zn-Zn atomic bonding lengths were deduced from EXAFS. It was revealed that the surface Mg amount increased with the increase in Ts. These comprehensive studies provide valuable references for Mg0.1Zn0.9O and other advanced materials.

Synthesis, Optical, and Magnetic Properties of the Mixed Chalcogenide Semiconductor Series Eu(II)2SiSexS4-x, Prepared via the Flux-Assisted Boron Chalcogen Mixture Method.

We report a detailed structural study of a series of five new quaternary Eu(II)-containing mixed chalcogenide phases, Eu2SiSe0.85S3.15, Eu2SiSe2.4S1.6, Eu2SiSe2.6S1.4, Eu2SiSe3.1S0.9, and Eu2SiSe4, synthesized using the flux-assisted boron chalcogen mixture (BCM) method. High-quality crystals were grown, and their crystal structures were determined by single-crystal X-ray diffraction. All members of the Eu2SiSexS4-x series crystallize in the monoclinic crystal system with space group P21/m, except Eu2SiSe4, which crystallizes in the P21 space group. The crystal structure of Eu2SiSexS4-x exhibits a complex three-dimensional network and is primarily composed of distorted trigonal prismatic EuQ6 polyhedra that are interconnected by SiQ4 tetrahedra. Polycrystalline powders were used for physical property measurements, including the magnetic susceptibility and UV-vis diffuse reflectance. Magnetic measurements indicated paramagnetic behavior with a slightly negative Weiss constant (θ = -13.54). The band gaps of the materials were determined from diffuse reflectance data, with optical band gaps estimated to be 2.04(2) eV, 1.98(2) eV, and 1.90(2) eV for Eu2SiSe0.85S3.15, Eu2SiSe2.6S1.4, and Eu2SiSe4, respectively. Band gap tuning was achieved by partially or fully replacing the S sites with Se.

Sc2CX2(X=O, S, Se) 2D-MXene materials for thermoelectric applications: A DFT study

MXene Sc2CX2(X = O, S, Se) have band gap tunability and are environmentally neutral, making them useful for future studies. In this current manuscript, we have theoretically investigated the physical traits of Sc2CX2(X = O, S, Se) using the FP-LAPW technique embedded in Wien2K simulations. These compounds exhibit thermodynamically, and structural stability confirmed through volume optimization curves. The electronic characteristics reveal indirect band gaps of these materials. The ultraviolet area is where materials absorb most light, indicating their potential for use in UV based optoelectronic devices. The transport traits examined depict the high PF values which demonstrate the importance of these compounds for renewable energies.

Flexible Fe-Doped NiO/Ni-Foam Substrate Nano-System Based Electrode with Tunable Opto-Electrochemical Attributes for Supercapacitor Applications

Abstract This work underlines the modification and effect of iron doping on different characteristics of NiO nanoparticles. The facile hydrothermal method was followed to form pristine and iron doped( 4% and 8% ) NiO sample. The X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy and Raman spectroscopy techniques were employed for the identification of phase, morphology, microstructural details and optical property of the as synthesized Fe doped NiO samples. XRD measurements of the as synthesized Fe doped NiO samples revealed the polycrystalline nature with the crystallite size varying from 11nm – 20nm showing hexagonal structure. Surface morphology investigation carried out by using SEM showed the varied morphology of as synthesized samples . UV-Vis investigation revealed a red shift with increasing iron doping content, which corresponds to a decrease in optical bandgap values from 3.4eV for pure NiO to 2.2eV for 8% Fe doped NiO sample thus giving a wide tunable absorption bandgap . The study of cyclovoltammetry and PEIS demonstrates the novelty of this work showing exceptionally high electrochemical performance in a three-electrode system with highest specific capacitance of 977F/g at scan rate of 20mV/sec for 8% doped sample .

Evolution of tunable energy bandgap and magnetic anisotropy in Mn substituted ferrimagnetic nickel-chromates

We report a detailed study on the composition (x) dependence of structural, electronic, magnetic, and optical studies of nickel chromate spinel (NiCr2O4) at various levels of Mn substitution at B sites. No significant structural distortion from cubic symmetryFd-3m was noticed for all the compositions in the range 0 ⩽x⩽ 1 of Ni(Cr1-xMnx)2O4. However, there is significant alteration in the bond angles∠B-O-B (90.51°-93.86°) and∠A-O-B (122.48°-124.90°) (both of which follow completely opposite trend with increasingx) and bond lengths A-O (1.82-1.94 Å) and B-O (2.02-2.08 Å). The corresponding lattice parameter (a) follows Vegard's law (8.32 ± 0.001 Å ⩽a⩽ 8.45 ± 0.001Å). The electronic structure determined from thex-ray photoelectron spectroscopy reveals the divalent nature of Ni (with spin-orbit splitting energy Δ ∼ 17.62 eV). While the Cr and Mn are stable with trivalent electronic states having Δ=8 and 11.7 eV, respectively. These results are in consonance with the cationic distribution (Ni)A[(Cr1-xMnx)2]BO4obtained from the Rietveld refinement analysis. Interestingly, the current series shows a direct bandgap (EG) semiconducting nature in whichEGvaries from 1.16 to 2.40 eV within the range ofx= 0.85-0. Such variation ofEG(x) is consistent with the compositional variation of the crystal structure data with anomalous change betweenx= 0.25 and 0.6. Beyond this range, theEgmode (140 cm-1) in Raman spectra arising from Mn-O octahedral decreases continuously and vanishes at higher Mn concentrations. Our analysis shows that all the investigated compounds show long-range ferrimagnetic ordering below the Néel temperature,TFNdue to the unequal magnetic moments of the cations. However, both the ordering temperatureTFNand saturation magnetization (MS) increases progressively from 73.3 K (1500 emu mol-1) to 116 K (3600 emu mol-1) with increasing the Mn content from 0 to 1, yet the maximum anisotropy (HK~4.5 kOe,K1~2.5 × 104erg cc-1) shows an opposite trend withx. Such variation is ascribed to the altered magnetic superexchange interactions between the cations located at A and B sites following the trendJBB>JAB>JAA, (JBB/kB=13.36 K).

Photoelectric characteristic of single-phase InxGa1-xN films with tunable bandgap through RF magnetron sputtering

Photoelectric characteristic of single-phase InxGa1-xN films with tunable bandgap through RF magnetron sputtering

Tuning the bandgap without compromising efficiency: ambient solution processing of Ge-alloyed (Ag,Cu)2Zn(Sn,Ge)(S,Se)4 kesterite thin-film solar cells

The photovoltaic sector currently experiences a growing demand for deeply-integrated technologies in agriculture, buildings, vehicles, among others. Kesterite compounds provide a versatile solution through their tunable bandgap via isovalent alloying. However, this should be done while preserving material opto-electronic quality and device performance, which is an unresolved challenge. Indeed, tuning the bandgap of kesterites must ensure low crystalline disorder to counteract the associated open-circuit voltage (Voc) losses when used in solar cells. To achieve this goal, this work introduces a simple molecular ink recipe realized in ambient air to process single-phase high-quality Ag,Gealloyed kesterite absorbers. By varying the Ge content from 0 to 100%, the absorber bandgap covers the range from 1.15 to 1.5 eV, in which the Urbach energy remains close to 20 meV and promisingly low Voc deficits are observed. In particular, the champion efficiency of 12.1% obtained with 40% Ge breaks the record for Ge-alloyed kesterites with a 1.2 eV bandgap by remarkably reaching 62% of the Shockley-Queisser limit for Voc. This study demonstrates a promising strategy to solve the issue of large band tailing and low opto-electronic quality in widebandgap kesterites while establishing a foundation for solution-processed kesterite solar cells with tunable bandgap and promising performance.

Analysis and Performance Evaluation of Non-Toxic Organo-Metal Halide (CH3NH3SnI3) Perovskite Optical Absorber based Photovoltaic Cell

Tin-based Perovskite solar cells (PSC) have emerged as a promising alternative to environmentally hazardous lead-based Perovskite solar cells. The lead-free Perovskite compound (CH3NH3SnI3) is particularly appealing due to its wide absorption spectrum. Perovskite materials both organic and inorganic, exhibit exceptional optical features such as a high absorption coefficient, a tunable band gap, and manufacturing techniques based on solution. The optical absorber material has been used in a novel solar cell composition ITO/TiO2/CH3NH3SnI3/NiO/Mo. To assess the device's performance, several critical parameters were investigated, including, structural layer thickness, carrier mobility, and the defect density. The numerical investigations were carried through solar capacitance simulator SCAPS-1D. By using calculations, Perovskite (CH3NH3SnI3) optical absorbent layer's thickness for the optimum device efficiency was adjusted to 1.032μm, for electron transport layer (ETL) TiO2 the thicknesses was 0.002μm and hole transport layer (HTL) NiO (HTL) optimized thickness was adjusted to be 0.02μm. The device power conversion efficiency (PCE) was found to be 21.068%. Electrical parameters open circuit voltage (Voc), short circuit current (Jsc), Fill Factor (FF %) and quantum efficiency (QE) get influenced by variation in layers thicknesses and interface defect densities. The proposed composition has been thoroughly investigated, and the optimized device performance has been comprehensively analyzed in this study. Current investigations may help to design and manufacture the environmentally acceptable, non-toxic, and efficient solar cells.

Design and analysis of pneumatic composite phononic crystal

Tuning band gaps in soft phononic crystal by air pressure-induced deformation is a feasible method to manipulate elastic waves. In this paper, we design a pneumatic composite phononic crystal that incorporates a labyrinthine structure into the Helmholtz-type phononic crystal. By calculating the band gaps of the representative volume element (RVE) arranged in a two-dimensional triangular lattice, we find that this design effectively extends the transmission path of sound waves, achieving band gaps in the vicinity of the lower frequency range. We apply pressure to the scatterer’s pneumatic actuator to adjust its volume through the deformation of soft material, altering the air filling rate and enabling reversible adjustment of the frequency and width of band gaps. Nonlinear finite element simulations investigate the effects of different pressure levels on the band gaps. Furthermore, we explore bandgaps tuning in one-dimensional phononic crystals and the impact of various types of point defects on the transmission characteristics of phononic crystals. Results show that the pneumatic phononic crystal exhibits rich band gaps under air pressure loading, in which a low-frequency band gap exists, and is capable of reversible continuous tuning. This study provides valuable for manipulating elastic waves in periodic structures and designing soft acoustic devices.

CsF Improved Buried Interface for Efficient and Stable Inverted All-inorganic CsPbI2.85Br0.15 Perovskite Solar Cells

All-inorganic CsPbIxBr3-x is frequently used as the top cells in tandem devices due to its tunable bandgap, making it highly promising for future development. However, CsPbIxBr3-x films typically contain numerous defects at the interfaces and grain boundaries, significantly hindering carrier transport and thus reducing the device performance. Interface modification is commonly employed to passivate defects and enhance carrier transport at the interfaces. In this work, CsF was used to modify the buried interface between the perovskite film and self-assembled monolayers (SAMs). The interaction between fluoride ions (F⁻) and uncoordinated Pb2⁺ contributed to reduce defect density, enhance crystallization quality, and suppress non-radiative carrier recombination at buried interface. Consequently, the efficiency of inverted CsPbI2.85Br0.25 PSCs with CsF improved from 16.15% to 18.24%, compared to the control device. Moreover, the unencapsulated CsF-modified device retained 89% of its initial efficiency after storing for 600 h in ambient air with room-temperature and relative humidity (RH) of 20%. This demonstrates that CsF modification significantly enhances both the performance and stability of CsPbI2.85Br0.15 perovskite solar cells.

Modelling of (N-vinylcarbazole)/Fullerene nanoheterojunction for organic solar cells and photovoltaics applications – A DFT Approach

The current manuscript depicts the construction of a novel hybrid carbon nanomaterials with fascinating electronic and chemical properties and tunable energy bandgap of a nano heterojunction comprising (9-vinyl carbazole), VK and fullerene, C60. A comprehensive investigation of VK/C60 adsorption surface is conducted using ab-initio density functional theory calculations with van der Waals corrections (GGA+vdW) implemented. The novel nanoheterostructure interfaces synthesized by DFT methods have low-bandgap characteristics (1.112–1.223 eV), broaden absorption wavelengths and photovoltaic characteristics. This novel VK/C60 nanoheterostructure composites have finite bandgaps and good stability and, therefore, have promising applications for photovoltaic devices. Optoelectronic features of all three developed systems are recommended for future solar cell applications. The studies reveal that the VK/C60 nanoheterojunctions can behave as efficient electron donor-acceptor components in organic solar cells (OSCs) that make them potential candidates for the development of low-cost optoelectronic devices. The band gap values calculated in this work are low enough to make the nanoheterostructures exceedingly promising for photovoltaic applications.

High-performance broad-spectrum self-powering photoelectrochemical photodetectors based on MnPSe3 nanosheets

Transition metal phosphorus trichalcogenides (MPX3), as a group of layered van der Waals materials with wide tunable bandgaps, high carrier mobility and good light absorption, are potential candidates for the preparation of high-performance broad-spectrum photoelectrochemical photodetectors (PEC PDs). MnPSe3, a p-type semiconducting material in the MPX3 family, was exfoliated into nanosheets using liquid-phase exfoliation, and then applied in the PEC PDs. The MnPSe3-based PEC PDs were thoroughly investigated in a three-electrode system and demonstrated self-powered photoelectric performance across a broad spectral range of 400-800nm. Specifically, under 400nm illumination, the photodetector showed the optimal performance with a photocurrent density of 9.72 μA/cm2, responsivity of 85.55 μA/W, response times of 10/15 ms and fine cyclic stability under the biased condition. In addition, effects of different stripping agents, bias voltages, wavelengths and optical powers on the device performance were compared. These findings suggest that MnPSe3 is a highly promising material in applications of high-performance self-powered PEC PDs.

Grading Approaches on CIGS Material for Improved Photovoltaic Applications

Copper indium gallium selenide (CIGS) solar cell has higher absorption coefficient, long-term reliability, and low construction cost. CIGS material has a tuneable bandgap that can be adjustable. In this article, study on CIGS solar cells has been performed, and strategies were proposed for maximizing efficiency using ‘‘grading”. SCAPS-1D tool has been used for numerical simulation. CIGS solar cell performance is investigated with graded profiles i.e., linear graded, parabolic graded, parabolic-2 graded, logarithmic graded, exponential function, beta function, power law and without a graded profile (uniform pure CIGS). The results show that cells performance appears to be significantly impacted by grading. Graded power law of CIGS solar cell has delivered power conversion efficiency (PCE) of 23.2%, however the efficiency achieved by ungraded CIGS solar cells is 17.46%. The parasitic resistance has been examined via various grading simulation tools.