Optimum Band Gap Research Articles

Optimization of Band Gaps in Rotors With Longitudinal Periodicity and Quasi-Periodicity

Abstract Structures with inertia periodicity present the phenomenon of band gap formation, i.e., the appearance of regions in the frequency spectrum with a higher modal spacing and lower vibration response. Rotating machines can also present such phenomenon when their working elements are mounted periodically along the shaft (longitudinal periodicity). In the present work, this phenomenon in rotating machines is reviewed, and it is shown that band gaps can be moved toward desired locations in the frequency spectrum by mounting the working elements at optimized positions along the shaft. For that, a mathematical model of the rotating machine is correlated to experimental results, and the model is used to optimize the position of the working elements (disks) in the rotor. The optimized rotor is then experimentally tested, and the resultant band gap is measured. The obtained experimental results show that one can indeed tailor the band gaps and move them toward higher or lower frequencies as desired without changing the inertia of the working elements.

Theoretical investigation of lattice-matched III-N-V/Si double-junction solar cells

The lattice-matched III-N-V/Si double-junction (DJ) solar cells are designed with GaNAsP and GaInNP top cells, respectively. Under AM1.5G condition, the efficiencies of III-N-V/Si DJ cells are calculated with variable electron lifetime (τe ) and electron surface recombination velocity (Se ) in top cell. When Se is 100 cm s−1 and τe rises from 1 to 1000 ns, the optimal efficiency of GaNAsP/Si cell increases from 31.12% to 36.13% due to the increasing short-circuit current and open-circuit voltage. With τe of 100 ns, the optimal efficiency keeps at a high value of ∼35% when Se changes from 10 to 1000 cm s−1, but drops obviously with Se of 10 000 cm s−1. In comparison, the optimal efficiency of GaNAsP/Si cell is less sensitive to Se than to τe . With fixed Se of 100 cm s−1, GaNAsP/Si cell shifts the optimal top-cell bandgap from 1.716 to 1.787 eV when raising τe from 1 to 1000 ns. However, the effect of Se on optimal top-cell bandgap is negligible. For III-N-V/Si cell with 100 ns τe and 100 cm s−1 Se , an optimal efficiency is obtained as ∼35.1%, which would be closer to the experimental limit owing to the expectable values of τe and Se . Furthermore, the optimal efficiency of GaNAsP/Si cell drops slightly when thinning Si substrate from 300 to 150 μm, but has a maximum of 35.95% with substrate doping of 1 × 1016 cm−3 when the doping concentration varies from 1 × 1015 to 1 × 1018 cm−3. The results and discussion in this work may act as a guidance for studying III-N-V/Si DJ cell.

Evolution of large-grained CuSbS2 thin films by rapid sulfurization of evaporated Cu–Sb precursor stacks for photovoltaics application

Ternary chalcostibite (CuSbS2) is a non-toxic and earth-abundant thin-film solar cell material with an optimal band gap, high optical absorption coefficient, and p-type electrical conductivity. Large-grained CuSbS2 thin films are crystallized by sulfurizing thermally evaporated Cu/Sb/Cu precursor stacks at 450 °C for a short duration of 1–10 min. The precursor stacks sulfurized at 450 °C for 1 min resulted in the formation of a Cu-deficient (to a small extent) and Sb-rich large-grained thin-films of CuSbS2 without any secondary phases. Increasing the sulfurization duration from 5 min to 10 min resulted in the formation of near-stoichiometric CuSbS2 films with columnar growth and more uniformly sized grains. The direct band gap of the films is found to be 1.42 eV. The electrical resistivity decreases from 28.6 to 16.7 Ω cm upon increasing the sulfurization duration from 1 to 10 min, respectively, and the hole mobility is in the range of 0.44–0.56 cm2 V−1 s−1. The solar cells fabricated using the CuSbS2 films sulfurized for a duration of 5 min exhibited a maximum power conversion efficiency of 2.5% with an open-circuit voltage of 568.7 mV and a short-circuit current density of 13.8 mA/cm2. This study provides a pathway for the development of high-efficiency CuSbS2 solar cells.

Multi-objective optimization of thermal expansion and adjustable band gap for a chiral triangular lattice metamaterial

Multi-objective optimization of thermal expansion and adjustable band gap for a chiral triangular lattice metamaterial

CuBiSe2 Quantum Dots as Ecofriendly Photosensitizers for Solar Cells

Cu-based ternary chalcogenides have shown high promise as low-cost ecofriendly alternatives to heavy-metal based photosensitizers. The successive ionic layer adsorption and reaction (SILAR) processed CuBiSe2 quantum dots possess an optimal bandgap, appealing photoresponsivity (excellent absorption coefficient of (10)5 cm–1), and photostability. Because of these advantageous properties, they have been investigated as photoabsorber materials for solar cells in this work for the first time. Use of such nontoxic and nonscarce materials, paired with low-temperature solution processing can address both concerns of environmental regulation and fabrication costs. The performance of the prototype solar cell developed has been satisfactory as a new emerging material (power conversion efficiency (PCE) of 2%) unlike the reported CuBiS2 showing a PCE of 0.68%. A further increase in efficiency was observed with the formation of a heterostructure CuBiSe2/CuBiS2 that exhibits a type-1 heterostructure and enables improvement in power conversion efficiency up to 2.6%. CuBiS2 acts as a passivation layer (reducing surface defects and recombination losses) and also as an absorber, facilitating confinement and longer lifetime of charge careers. A detailed investigation of these Cu based selenium quantum dots and the insights provided into their electronic structure and dynamics in this work would significantly influence the future research of these materials into other optoelectronic applications.

Synthesis and optimization of SnS absorber layer by spin-coating process and Taguchi approach

In this paper, a synthesis of SnS thin films using sol-gel spin coating method and optimization of the parameters influencing the experimental process. Taguchi experiment design with a L9(34) orthogonal array was used to optimize several parameters such as the annealing temperature, annealing time, concentration, and [S]/[Sn] ratio. To perform the necessary tests three levels of each factor were chosen. The analysis of variance (ANOVA) and signal-to-noise (S/N) was used to obtain the good optical properties (optimal band-gap) at the best combination of choosing factors. The obtained results indicate that the most influencing factors in the preparation of SnS thin films are the concentration and the [S]/[Sn] ratio. To confirm the results obtained, the test validation was performed using the optimal conditions. SnS thin films obtained at optimal condition were analyzed using X-Ray diffraction, UV–visible spectrophotometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and four-point probe.

Numerical Simulation of the Performance of Sb2Se3 Solar Cell via Optimizing the Optoelectronic Properties Based SCAPS-1D.

Antimony trisulfide (Sb2Se3), a non-toxic and accessible substance, has possibilities as a material for use in solar cells. The current study numerically analyses Sb2Se3 solar cells through the program Solar Cell Capacitance Simulator (SCAPS). A detailed simulation and analysis of the influence of the Sb2Se3 layer’s thickness, defect density, band gap, energy level, and carrier concentration on the devices’ performance are carried out. The results indicate that a good device performance is guaranteed with the following values in the Sb2Se3 layer: an 800 optimal thickness for the Sb2Se3 absorber; less than 1015 cm−3 for the absorber defect density; a 1.2 eV optimum band gap; a 0.1 eV energy level (above the valence band); and a 1014 cm−3 carrier concentration. The highest efficiency of 30% can be attained following optimization of diverse parameters. The simulation outcomes offer beneficial insights and directions for designing and engineering Sb2Se3 solar cells.

Enhanced Performance of CuIn1-xGxSe2 Solar Cell Through Optimization of Absorber and Buffer Layer Properties Using SCAPS-1D

This study is a follow up to our previously published article on “Numerical Simulation of Copper Indium Gallium Diselenide Solar Cells Using One Dimensional SCAPS Software”. Five more parameters were optimized which are: absorber band gap, absorber electron affinity, buffer layer band gap, buffer layer electron affinity and working temperature using the same simulation tool initially used. When the absorber bandgap was varied between 0.8 eV and 1.6 eV, the efficiency of the solar cell increases until it reached its peak at 27.81%. This occurred at absorber bandgap of 1.4 eV. Other photovoltaic parameters at this optimum value are: Voc of 1.00 V, Jsc of 31.99 mA/cm2 and FF of 87.47 %. On varying the absorber electron affinity from 4.20 eV through 4.55 eV, we obtained an optimum value of 4.45 eV at Voc of 0.82 V, Jsc of 37.96 mA/cm2, FF of 84.99 % and an efficiency of 26.36%. The optimization of buffer bandgap resulted in an optimal value of 3.0 eV, when the buffer bandgap was varied between 1.6 eV and 3.2 eV. The photovoltaic parameters at this optimal value are: Voc of 0.80 V, Jsc of 37.96 mA/cm2, FF of 85.22 % and an efficiency of 25.86%. The effect of buffer electron affinity was studied by varying its value between 4.00 eV and 4.40 eV and its best value was found to be 4.05 eV at photovoltaic parameters with a Voc of 0.82 V, Jsc of 37.96 mA/cm2, FF of 84.98 % and an efficiency of 26.36 %. These optimized values in all parameters were used to simulate a solar cell which resulted to device with performances: Voc of 1.11 V, Jsc of 31.50 mA/cm2, FF of 88.91 % and an efficiency of 31.11 %. On varying the working temperature on the optimized solar cell, the optimized device with its best performance at 270 K with Photovoltaic (PV) values of Voc of 1.15 V, Jsc of 31.55 mA/cm2, FF of 88.64 % and an efficiency of 32.18%. The results obtained were encouraging and can serve as a guide to those involved in practical development of solar cells.

Efficient Perovskite Indoor Photovoltaics with Open-Circuit Voltage of 1.15V via Collaborative Optimization of CsPbI2 Br Layer and Hole Transport Layer.

All-inorganic CsPbI2 Br perovskite has attracted great attention due to the stable crystal structure and moisture resistance, and its 1.91eV bandgap is close to the optimal bandgap of indoor artificial light sources, making it be the best candidate for the indoor photovoltaics (IPVs) to power a wide range of internet of things related electronic devices. Herein, we report on the preparation of CsPbI2 Br with α-phase and the improvement of its phase stability by adding lead acetate in the CsPbI2 Br precursor. A series of dopant-free conjugated polymers (P3HT, PBDB-T, and PM6) with different highest occupied molecular orbital energy levels are introduced as hole transport layers for building IPV devices. The PM6 based devices having better energy alignment with perovskite demonstrate best indoor photovoltaic performance, giving a remarkable open-circuit voltage of 1.15V and high fill factor of 81.86% under 1000 lux (330 µW cm-2 ) light-emitting diode illumination, and finally realizing a decent power conversion efficiency of 33.68%. Our findings suggest that collaboratively optimize the CsPbI2 Br layer and hole transport layer is an effective approach to realize high performance IPVs.

Development of 2nd Generation Thin Film Photovoltaics Based on CZTS Absorber Layer and ZnS Window Layer

Among the second-generation solar cells, thin-film solar cells based on CIGS, CZTS and CdTe are well known due to their higher efficiencies, low cost and simple fabrication techniques. In this proposed work, we are committed to developing CZTS and ZnS thin films for second-generation thin-film photovoltaics. CZTS and ZnS have energy band gap of 1.4-1.5 eV and 3.6 eV, while their light absorption coefficients are 104 cm-1 and 3.3×104 cm-1 respectively. In thin film solar cells, absorber layer consists of photovoltaic material that should have optimal bandgap close to 1.34 eV. Moreover, a wide band gap window layer acts as p-n junction with absorber layer. In this work, we are reporting the synthesis of CZTS and ZnS thin films via wet chemistry route using spin coating method. Deposition of thin films on SLG substrate were carried out at specific process parameters such as spinning speed, concentration of precursors and annealing temperature to get the optimized thin film suitable for photovoltaic applications. Surface morphology and elemental compositional analysis investigated through SEM and EDX spectroscopy respectively. Electrical and optical properties were examined via Hall effect measurements and UV-VIS NIR spectrophotometry respectively. In addition micro-chemical and functional group analysis were conducted by FRIT spectroscopy. Keywords: Thin film PV, wet-chemistry, CZTS, ZnS

Panchromatic oxasmaragdyrin as dual functional hole‐transporting material in all‐inorganic CsPbIBr2 perovskite solar cells

AbstractAll‐inorganic perovskite CsPbIBr2 offers both an optimal bandgap and good stability. The perovskite solar cells (PSCs) with CsPbIBr2 as a solar harvester utilize mainly spiro‐OMeTAD as a hole‐transporting material (HTM). Still, these PSCs are prone to degradation and not cost‐effective. Herein we examined, for the first time, a metal‐free dimethoxyboranyl (B(OR)2) chelated oxasmaragdyrin, SM‐OMe, as an alternative bifunctional HTM for CsPbIBr2‐based PSCs to demonstrate promising power conversion efficiencies at lower costs. The devices with SM‐OMe as HTM outperform spiro‐OMeTAD‐based devices with the highest power conversion efficiency of 6.04%. This enhanced performance can be attributed to an HTM and sensitizer dual‐function of SM‐OMe, which extends the absorption edge and consequently improves the short circuit current density. Furthermore, SM‐OMe‐based devices exhibited better charge extracting and hole‐transporting properties. Hence, this study demonstrates an effective and successful utilization of a new HTM with a bifunctional role as an alternative to conventional spiro‐OMeTAD in all‐inorganic PSCs.

Theoretic efficiency limit and design criteria of solar photovoltaics with high visual perceptibility

Building facades and rooftops provide extensive potential areas for photovoltaic (PV) installation, enabling building-integrated PVs (BIPV) of great interest. PV panels' poor aesthetics, on the other hand, are a key barrier to the wider adoption of BIPV. Although certain PV colorization methods have been developed, the colors obtained are still restricted, particularly those brilliant and low-saturation hues that are desirable for architectural decoration. One concern, therefore, arises whether solar PV can attain high visual perceptibility while also being efficient. To answer this question, here we present a thorough analysis that has quantified the Shockley-Queisser efficiency limits of ideal opaque solar cells with varying lightness. Furthermore, we establish a method for estimating the performance of a real solar cell after colorization. The results suggest that for ideal solar cells with neutral colors that have lightness over 80, the highest efficiency could range between 20.4 % and 25.9 %, with an optimum bandgap between 0.95 and 1.15 eV. The absolute value of over 2 % in efficiency could be further improved if the optimal reflectance is applied to minimize efficiency loss. For the current state-of-the-art solar cell technology, an efficiency limit of 19.8 % is available with the pure white color (RAL 9001). As a result, it could be estimated that silicon solar cells with high visual perceptibility and efficiency limits between 15.4 % and 20.4 % are practically achievable. This study demonstrates its theoretical feasibility, and also inspires the design criteria and evaluation method for practical implementation of solar PVs with high visual perceptibility.

Bandgap optimization in combinatorial graphs with tailored ground states: application in quantum annealing

A mixed-integer linear programming (MILP) formulation is presented for parameter estimation of the Potts model. Two algorithms are developed; the first method estimates the parameters such that the set of ground states replicate the user-prescribed data set; the second method allows the user to prescribe the ground states multiplicity. In both instances, the optimization process ensures that the bandgap is maximized. Consequently, the model parameter efficiently describes the user data for a broad range of temperatures. This is useful in the development of energy-based graph models to be simulated on Quantum annealing hardware where the exact simulation temperature is unknown. Computationally, the memory requirement in this method grows exponentially with the graph size. Therefore, this method can only be practically applied to small graphs. Such applications include learning of small generative classifiers and spin-lattice model with energy described by Ising hamiltonian. Learning large data sets poses no extra cost to this method; however, applications involving the learning of high dimensional data are out of scope.

Dion-Jacobson phase lead-free halide (PDA)MX4 (M=Sn/Ge; X=I/Br/Cl) perovskites: A first-principles theory

Hybrid lead (Pb) halide perovskites are widely regarded as promising materials for next generation of photovoltaic (PV) and optoelectronic (OE) devices owing to their high power conversion efficiency (PCE). To obtain green lead-free and excellent materials, the structural, electronic and optical properties of tin (Sn) and germanium (Ge) based single-layer Dion-Jacobson (DJ) phase perovskites (PDA)MX4 (M ​= ​Sn/Ge; X ​= ​I/Br/Cl) systems are investigated by carrying out first-principles theory. The calculation results indicate that all perovskites (PDA)MX4 have good thermal stability (at 300K), and the structural stability increases in the order of I–Br–Cl. These compounds are direct bandgap semiconductors, ranging from 1.26 to 1.81 ​eV ((PDA)SnX4) and 1.44–2.26 ​eV ((PDA)GeX4). Density of states (DOS) reveals that the band edge state mainly comes from the M-X bond and the organic molecule PDA is not directly involved in the contribution. Compared to Ge-based perovskites, the bandgap range of Sn-based perovskites is not only closer to the optimal bandgap requirement for perovskite solar cells (PSCs), but the optical properties reveal a slightly higher absorption coefficient for Sn-based perovskites in the visible light range. This suggests that (PDA)SnX4 perovskites are more favorable for PSCs applications. The theoretical study can provide strong support for the development of high-level perovskites materials in PV and OE devices.

Visible Light Mediated Heck Coupling of Inactivated Aryl Fluoride/Chloride Over a Sulfonic Acid Functionalized, Melamine‐based Metal‐free Porphyrin Photocatalyst

AbstractWe report the synthesis of a new, sulfonic acid functionalized, melamine‐based metal‐free porphyrin photocatalyst (MBMFPc) for the C−C coupling of the most unreactive aryl halides with alkenes under visible light irradiation. The ionic liquid‐based photocatalyst was characterized using various analytical techniques Proton Nuclear Magnetic Resonance (1HNMR) Spectroscopy, Carbon Nuclear Magnetic Resonance (13CNMR) Spectroscopy, Fourier Transformed Infrared Spectroscopy (FT‐IR), Energy‐dispersive X‐ray Spectroscopy (EDAX), Scanning Electron Microscope (SEM), Brunauer‐Emmett‐Teller (B.E.T) and Ultraviolet‐Visible Spectroscopy (UV‐Vis). The MBMFPc photocatalyst with noticeable Hammett acidity (0.56) and optimal bandgap of 1.44 eV was found to as an effective catalyst in the Mizoroki‐Heck coupling of inactivated aryl fluoride/chloride using 5 W LED in a homemade photoreactor under ambient conditions. The protocol comprising metal‐free green photocatalyst tolerated a variety of aliphatic/aromatic alkenes bearing different substituents afforded good to excellent yields. The role of photogenerated excitons was confirmed by scavenger studies with K2S2O8 and EDTA. The leaching test, stability, and reusability of MBMFPc photocatalyst evidenced as a perfect heterogeneous photocatalyst and afford appreciable yield (80 %) after 5 cycles. A plausible mechanism for photocatalytic C−C coupling has been proposed and described. A metal‐free acid‐functionalized ionic liquid‐based MBMFPc photocatalyst with appreciable TON (4,51,948) and TOF (22,597 h−1) could gain significant attraction as a green catalyst in the pharmaceutical industries for the synthesis of intermediates by C−C coupling using commercial aryl chlorides.

Phase-Stable Wide-Bandgap Perovskites for Four-Terminal Perovskite/Silicon Tandem Solar Cells with Over 30% Efficiency.

Wide-bandgap perovskite solar cells (PSCs) with an optimal bandgap between 1.7 and 1.8eV are critical to realize highly efficient and cost-competitive silicon tandem solar cells (TSCs). However, such wide-bandgap PSCs easily suffer from phase segregation, leading to performance degradation under operation. Here, it is evident that ammonium diethyldithiocarbamate (ADDC) can reduce the detrimental I2 back to I- in precursor solution, thereby reducing the density of deep level traps in perovskite films. The resultant perovskite film exhibits great phase stability under continuous illumination and 30-60% relative humidity conditions. Due to the suppression of defect proliferation and ion migration, the PSCs deliver great operation stability which retain over 90% of the initial power conversion efficiency (PCE) after 500 h maximum power point tracking. Finally, a highly efficient semitransparent PSC with a tailored bandgap of 1.77eV, achieving a PCE approaching 18.6% with a groundbreaking open-circuit voltage (VOC ) of 1.24V enabled by ADDC additive in perovskite films is demonstrated. Integrated with a bottom silicon solar cell, a four-terminal (4T) TSC with a PCE of 30.24% is achieved, which is one of the highest efficiencies in 4T perovskite/silicon TSCs.

Optical and Structural Study of the CZTS (Cu2ZnSnS4) Thin Film for Solar Cell Derived from the Chloride-Based sol-gel Precursor Solution

Fabrication of environmentally safe C2ZnSnS4 (CZTS) photovoltaic thin films of pure kesterite state is crucial. We have preparedCZTS thin films by sol-gel dip-coating process from chloride-based chemicals. After vacuum-annealed at 550°C, the optical andstructural characters of the films were further examined by UV–vis spectroscopy, X-ray diffraction (XRD), scanning electronmicroscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) methods. The CZTS films offered high optical absorption(0.4x104cm-1) and nearly optimum bandgap energy (1.65e V). X-ray diffraction examination confirmed the kesterite structure offilms. Scanning electron micrograph affirmed the creation of jam-packed, condensed and granulated CZTS films. The thin filmdisplayed intermittent disposal of agglomerated particles with clear-cut edges. The energy dispersive X-ray spectroscopy study gavethe stoichiometric ratio as Cu: Zn: Sn: S= 2.2: 1.4: 1: 5.1.
 Dhaka Univ. J. Sci. 70(1): 1-7, 2022 (January)

Efficient Ideal‐Bandgap Tin–Lead Alloyed Inorganic Perovskite Solar Cells Enabled by Structural Dimension Engineering

AbstractInorganic tin–lead alloyed perovskite solar cells with optimal bandgap have gained increasing attention because of their higher theoretical efficiency limit, inherently robust stability, and potentials in all‐inorganic perovskite tandems. However, their efficiency has far lagged from their Pb‐based counterparts owing to some intractable problems such as poor crystallization and facile Sn2+oxidation. Here, a small amount of 2D perovskite PEAPb0.7Sn0.3I4is utilized to regulate the crystallization process of 3D CsPb0.7Sn0.3I3based on the temperature‐gradient annealing method. The X‐ray diffraction results show that a stable intermediate phase composed of 3D perovskite seeds and 2D phases is formed under a lower annealing temperature of 50 °C, and the pre‐crystallized 3D perovskites can promote the subsequent crystallization upon 80 °C annealing to attain high quality film. It is interesting that the 2D perovskite phase is ultimately mainly located between the 3D perovskite phase and hole transport layer as revealed by the time of flight‐secondary ion mass spectrometry. The resulting perovskite exhibits a lower extent of non‐radiative recombination and better stability. Consequently, the device achieves a champion efficiency of 14.6% setting a new record for inorganic tin‐lead perovskite solar cells (PSCs). This work sheds more light on the future progress of inorganic tin‐lead PSC.

A locally resonant phononic crystal structure with low-frequency broad bandgap

The vibration induced by low-frequency elastic wave reduces the working accuracy of precision instruments. The locally resonant phononic crystal provides a feasible measure for low-frequency vibration isolation because of its bandgap characteristics. In this paper, a locally resonant phononic crystal structure with a broad bandgap is proposed, which consists of a periodic phononic crystal plate with double-sided steel stubs coated by rubber layers. Through finite element analysis, it can be found that the proposed structure can produce a bandgap with 355 Hz bandwidth within the range of 0–500 Hz and isolate vibration in the range of bandgap. By analyzing the local resonance modes of the proposed structure, we further propose the equivalent mass–spring model to predict its bandgap range. The predicted bandgap results from equivalent models of the proposed structure agree well with the results from the finite element analysis. These equivalent models provide an effective and simple method for bandgap optimization of the proposed phononic crystal structure.

Tuning bandgap and energy stability of Organic-Inorganic halide perovskites through surface engineering

Organohalide perovskite with a variety of surface structures and morphologies have shown promising potential owing to the choice of the type of heterostructure dependent stability. We systematically investigate and discuss the impact of 2-dimensional molybdenum-disulphide (MoS2), molybdenum-diselenide (MoSe2), tungsten-disulphide (WS2), tungsten-diselenide (WSe2), boron-nitiride (BN) and graphene monolayers on bandgap and energy stability of organic–inorganic halide perovskites. We found that MAPbI3 deposited on BN-ML shows room temperature stability (-25 meV ∼ 300 K) with an optimal bandgap of ∼ 1.68 eV. The calculated absorption coefficient also lies in the visible-light range with a maximum of 4.9 × 104 cm−1 achieved at 2.8 eV photon energy. On the basis of our calculations, we suggest that the encapsulation of an organic–inorganic halide perovskite monolayers by semiconducting monolayers potentially provides greater flexibility for tuning the energy stability and the bandgap.