Optimum Band Gap Research Articles

Simulation Based Investigation on the Performance of Metal Oxides as Charge Transport Layers in Lead/Tin Perovskite Solar Cells Using SCAPS 1D

Perovskite solar cells have been in the lime-light of emerging photovoltaic technology owing to their rapid rise in efficiency. The solar capacitance simulator (SCAPS −1D) is a simulation tool that can be used to investigate on the factors that affect the performance of planar perovskite solar cells. In this work, a simulation model has been developed to investigate the performance of metal oxides as charge transport layers for lead and tin based perovskite solar cells. The simulation study on the optimization of energy band gap and electron affinity of ZnO electron transport material with lead/tin perovskite using inorganic metal oxide Cu2O as hole transport materials is done. The influence of trap defect density (Nt) and acceptor doping concentration (Na) of the perovskite layer on the solar cell performance is also evaluated. The doping concentration and defect density of the perovskite layer greatly influence the recombination rate which determines the efficiency of perovskite solar cell.The common p type metal oxides CuO and NiO are experimented for the perovskite solar cell using lead/tin perovskite. The simulation results prove Cu2O as the best metal oxide hole transport material that can be utilized for efficient ZnO based perovskite solar cells.

Y-shape structured azo dyes with self-transforming feature to zwitterionic form as sensitizer for DSSC and DFT investigation of their photophysical and charge transfer properties

Two novel azo dyes with D-π-A-π-D structures were designed and synthesized to investigate the relationship between molecular structure and sensitizing performance on applying for dye-sensitized solar cells (DSSCs) in comparison with their linear counterparts. Introducing hydroxyl auxiliary groups and arranging π-conjugation length as two parallel and series structural architectures, Y-shape and linear, led to red shift in absorption wavelength and increase in absorption intensity for the Y-shape pattern providing an efficient charge transfer pathway and improved Jsc and η of the DSSCs. Emerging a zwitterionic form, azonium structure, of the sensitizer in parallel configuration for the dyes 1a.p and 1b.p, enhanced light absorption domain and changed anchoring fashion could engendering improved electronic overlapping. The easily–synthesized dyes were evaluated for photophysical and electrochemical properties and turned out that the parallel-decorated dyes displayed better results than the series types as photosensitizers for DSSCs. ATR and Raman spectra clearly showed the adsorption of these dyes on the TiO2 surface. Operational tests of DSSCs, coated by titled azo dyes, illustrated that decorating π-conjugation pattern as parallel structure as well as accessorizing the donor unit with hydroxyl groups improved the photovoltaic performance. Optimized band gap due to participating the azonium structure and restricted electron recombination as well as rectified dye regeneration were proposed as main elements in enhancing performance parameters. A higher solar conversion efficiency was recorded for DSSCs based on the Y-shape dyes compared to other meta azo dye-based cells that were previously reported. Computational calculations were used to corroborate the opto-electrochemical traits of the dyes with a special concern on the influence of structural pattern on photovoltaic features.

Light absorption and photocatalytic activity enhanced by in situ formation of uniform TiO2 nanoparticles on two-dimensional Ti3C2Tx surface

Ti3C2Tx surface was functionalized with uniform TiO2 nanoparticles (NPs) to form layered TiO2/Ti3C2Tx heterojunctions by an in situ solvothermal oxidation method. The resulting TiO2 NPs were connected to Ti3C2Tx species via O–Ti–O bonds. The TiO2/Ti3C2Tx (TT-190) heterojunctions exhibited the optimal bandgap of 2.11 eV at a reaction temperature of 190 °C, which was favorable for the absorption of visible light. The photocatalytic activity of TT-190 was examined by studying the photodegradation of mono-azo dye methylene red (MR) and di-azo dye congo red (CR). The MR degradation rate over TT-190 exceeded 96.1% after 120 min of irradiation with a 300 W xenon lamp, while the CR degradation rate over TT-190 under the same conditions was only 87.5%. The enhanced photocatalytic performance for azo dye degradation with TT-190 derive from the charge transfer and the generation of active radical species ·O2–. This work provides an alternative method for the fabrication of controllable uniform TiO2 NPs on the two-dimensional Ti3C2Tx surface, thus improving its photocatalytic activity.

Machine learning prediction of the optimal carrier concentration and band gap of quaternary thermoelectric materials via element feature descriptors

AbstractWhile the thermoelectric (TE) materials have attracted significant attention in recent years, the design and discovery of new TE materials with optimal carrier concentration and band gap remains a great challenge. Herein, we report the development of machine learning (ML) methods to predict TE materials with introducing physically meaningful simple descriptors. Specifically, we use the number of electrons, Pauling electronegativity and relative atomic mass as the basic physical variables and compute 242 descriptors in 64 categories to characterize the molecular information of a TE material. Multiple stepwise regression is employed to reduce the dimensionality in the developed ML models, and 5 and 4 important features for the band gap and carrier concentration is selected, respectively. The important features are used as input of a total number of 19 ML methods to select the optimal ML models for the prediction of band gap and carrier concentration, respectively. It is shown that the least square support vector machines method is the best model for the prediction of the band gap, while the back propagating artificial neutral network model exhibits the best performance in predicting the carrier concentration values. This work provides novel theoretical guidance for the rapid prediction properties of TE materials. The simple descriptors we defined can accurately predict the band gap and carrier concentration of quaternary TE materials.

Performance analysis and optimization of band gap of terahertz antenna for WBAN applications

Nano antennas for wireless body applications are designed for in-vivo body monitoring and screening on Terahertz frequency band in higher optical range. The frequency range has been used to design an antenna with band gap introduced between radiating patch and feedline, the light is injected in a patch through a Nano port. Considering wireless body area network application, the proposed design of antenna has a patch of gold, slotted ground, and a substrate of Gallium Arsenide with dimensions of proposed design as 286 × 144 × 120.1 nm3. The band gap has been optimized using artificial neural network (ANN), and a mean squared error is generated to acquire the best possible results. The designed Nano antenna’s characteristics exhibit an effective return loss of −48.58 dB and a gain of 2.995 dB at an optimized resonant frequency of 223.89 THz. In this work other antenna parameters such as surface current, current density and VSWR are also analyzed. The simulations are performed in Computer Simulation Technology (CST) Microwave Studio and shows successful results in higher optical range. Promising results have been depicted at higher optical ranges of Terahertz band.

Binary-Like Topology Optimization of Piezoelectric Metamaterial Plate with Interface Circuits Using Extended Plane Wave Expansion Method

Piezoelectric metamaterial plate (PMP) is being investigated for structural vibration energy harvesting (SVEH), in which an interface circuit is often used. Thus, it is a challenge to perform bandgap optimization of such an elastic–electro–mechanical coupling system. This paper presents a binary-like topology optimization scheme by dividing the unit cell into identical pieces, where a {0, 1} matrix is optimized to indicate material distribution. Firstly, a unified motion equation is derived for the elastic plate and the piezoelectric patch, and an electromechanical coupling model is built for a self-powered synchronized charge extraction circuit. Then, an extended plane wave expansion method is presented to model the bandgap character of the PMP with interface circuits (PMPICs), and the numerical solution of the dispersion curves is derived based on the Bloch theorem. Next, an extended genetic algorithm is applied for the topology optimization of the PMPIC. In the end, numerical and finite element simulations are performed to validate the proposed method. The results demonstrate that both the structure and the circuit can be optimized simultaneously to obtain the maximum first-order bandgap at a given central frequency. Therefore, the proposed method should provide an effective solution for the topology optimization of a PMPIC for broadband SVEH.

Bandgap optimization of sol–gel-derived TiO2 and its effect on the photodegradation of formic acid

This work reports a key factor, the H2SO4 concentration, in controlling the physicochemical properties of titanium dioxide (TiO2) photocatalysts during the sol–gel synthesis. The photocatalysts synthesized using different concentrations of H2SO4 possess specific anatase/rutile ratios and crystallite sizes as well as surface areas, resulting in different photocatalytic performance in the degradation of formic acid in solution. The best photocatalytic performance is observed for the TiO2 photocatalyst containing a relatively high percentage of the rutile phase (∼84%), which is obtained from the sol–gel synthesis without H2SO4.

The correlation between limiting efficiency of indoor photovoltaics and spectral characteristics of multi-color white LED sources

The correlation between the optimal performance of indoor photovoltaics (IPVs) and spectral characteristics of white light-emitting diode (LED) sources has been investigated theoretically. We calculated the Schockley–Queisser limit of IPVs under multi-color white LEDs with different correlated color temperature (CCT), color rendering index (CRI) and luminous efficacy of radiation (LER). It is found that the optimal bandgap for an IPV cell is not only influenced by CCT, but also by LER and CRI. However, the main factor that affects the maximum power conversion efficiency (PCE) is CCT, and the maximum PCE is relatively independent of the CRI and LER under the same condition of CCT. The maximum PCE decreases with the increase of CCT. Based on the analysis of the energy loss within IPVs, it is found that the value of the optimal bandgap is sensitive to the fraction of red light in the spectrum of white LEDs. The maximum PCE is primarily limited by the relaxation to band edge loss, which is caused by the high-energy blue or cyan light in the spectrum of white LEDs.

Feature-Rich Geometric and Electronic Properties of Carbon Nanoscrolls.

How to form carbon nanoscrolls with non-uniform curvatures is worthy of a detailed investigation. The first-principles method is suitable for studying the combined effects due to the finite-size confinement, the edge-dependent interactions, the interlayer atomic interactions, the mechanical strains, and the magnetic configurations. The complex mechanisms can induce unusual essential properties, e.g., the optimal structures, magnetism, band gaps and energy dispersions. To reach a stable spiral profile, the requirements on the critical nanoribbon width and overlapping length will be thoroughly explored by evaluating the width-dependent scrolling energies. A comparison of formation energy between armchair and zigzag nanoscrolls is useful in understanding the experimental characterizations. The spin-up and spin-down distributions near the zigzag edges are examined for their magnetic environments. This accounts for the conservation or destruction of spin degeneracy. The various curved surfaces on a relaxed nanoscroll will create complicated multi-orbital hybridizations so that the low-lying energy dispersions and energy gaps are expected to be very sensitive to ribbon width, especially for those of armchair systems. Finally, the planar, curved, folded, and scrolled graphene nanoribbons are compared with one another to illustrate the geometry-induced diversity.

A two-grid method for the phase-field model of photonic band gap optimization

A two-grid method is proposed to solve phase field models, arising from modeling the band gap optimization of photonic crystal design based on the Transverse Electric field (TE mode). In our approach, finite element methods on nested grids are used to solve different Partial Differential Equations (PDEs), say, the Hemholtz equation for the state constrain and the phase field equation for topology evolving, respectively. Dicretization on the coarse and fine grids are performed to balance the costs between the phase evolving and state equation solver. To fuse the two scheme together, additional correction step is necessary in two-grid settings. Furthermore, convergence analysis for the proposed two-grid scheme is established. Finally, numerical examples are presented to show the efficiency and robustness, and it is illustrated that the two-grid method improves the speed of computation while remain the computational accuracy.

The effects of composite primitive cells on band gap property of locally resonant phononic crystal

Locally resonant phononic crystal (LRPC) has the extraordinary property to prohibit the wave propagation in specific low-frequency ranges, however it exists limitation in engineering application due to narrow band gap width. Extensive achievements have been obtained on the locally resonant band gap (LRBG) tunability, whereas existing investigations mainly concern the independent primitive cells structure, which have the limitation in obtaining low-frequency and broadband simultaneously. In this paper, the composited locally resonant phononic crystals (CLRPC) are proposed and the effects of primitive cells contact state on the LRBG properties are investigated. The dispersion curves are applied to obtain the LRBG, and the corresponding modal features are analyzed to explain the band gap formation mechanism. The band structure indicates the design of composite primitive cells is able to increase the band gap number and obtain lower band gap, which is verified by the frequency response function (FRF). For the band gap formation mechanism, the asymmetric vibration due to primitive cells contact leads to diverse and strong coupling response, which generates more band gaps and reduces the band gap starting frequency, therefore the band gaps can be tuned by designing carefully the geometry structure of CLRPC. Further researches on band gap optimization demonstrate that the smaller cell spacing, smaller lattice constant and larger damping of coating layer should be satisfied to obtain broader LRBG and considerable attenuation synchronously. This investigation can provide references for the locally resonant isolation structure design in the low-frequency vibration control field.

Suitable Top Cell Partners for Copper Indium Gallium Selenide‐Based Tandem Solar Cells to Achieve >30% Efficiency

A four‐terminal tandem structure based on the copper indium gallium selenide (CIGS) solar cell is a viable approach to achieve high efficiency. For this purpose, a dual‐junction configuration, consisting of the experimental CIGS cell with a record efficiency of 23.35% as the bottom cell and wide bandgap thin‐film solar absorbers as the top cell, is evaluated by modeling. Herein, the effects of luminescence efficiency, optical absorption, bandgap, thickness, and light trapping of the top cell on the designed tandem performance are investigated. The results show that the optimum bandgap and the thickness of the absorber layer for the top cell are between 1.7 and 2 eV and 0.5 μm, respectively. Light trapping for less than 1 μm‐thick top cell has a strong impact on cell performance. The analytical model for the tandem solar cell is provided to recognize the suitable materials as the partner for the CIGS cell. The analysis shows that the gallium arsenide (GaAs), copper zinc tin sulfide (CZTS), cadmium telluride (CdTe), and copper gallium selenide (CGS) thin‐film solar cells can be considered suitable top cells to achieve a tandem cell with more than 30% efficiency. The Al0.31Ga0.69As/CIGS tandem solar cells with 35.9% efficiency are also proposed.

Effect of substrate temperature on the growth of CuSbS2 thin films by chemical spray pyrolysis

CuSbS2 is an emerging potential compound semiconductor for absorber layer in thin film heterojunction solar cell. Spray pyrolysis technique has been successfully employed to deposit CuSbS2 thin films onto soda-lime glass substrates held at different substrate temperatures in the range of 220 °C–280 °C. The structural and optical analysis revealed that films deposited at 260 °C are CuSbS2 with chalcostibite structure. The films deposited at other substrate temperatures contained binary/ternary phases like Cu2-xS, Cu3SbS4 and Cu12Sb4S13. The lattice parameters of CuSbS2 films are found to be a = 0.599 nm, b = 0.379 nm and c = 1.449 nm respectively. The band gap of CuSbS2 films is close to the optimum band gap (1.5eV) required for highest theoretical photovoltaic conversion efficiency. The optical absorption coefficient value lies in the range of 104 cm−1. The nature of these films is found to be p-type.

Emerging Organic/Hybrid Photovoltaic Cells for Indoor Applications: Recent Advances and Perspectives

Due to the continuous development and advances in the Internet of Things, wireless sensors, actuators for human−interactive machines, and indoor low‐power devices require a continuous supply of energy. Photovoltaic cells working under indoor light are suitable candidates for charging these devices because of their high voltages (up to 5 V), low costs, and environmental friendliness. Herein, the research on organic photovoltaic, dye‐sensitized, and perovskite cells in indoor photovoltaic applications with respect to the active layer, modified layer, and preparation process is summarized. The performance enhancement of indoor photovoltaic cells is outlined, including photoactive material selection, bandgap optimization, modification layer function, and device structure design, followed by the prospects and challenges of future developments in indoor photovoltaic cells. With this review an important perspective for the advancement of indoor photovoltaics is offered.

Hierarchical layered nanostructure of MoS2/boron doped reduced graphene oxide composites under visible light irradiation for effective antibiotic degradation and hexavalent chromium reduction

Hierarchical layered structures of dichalcogenides have assumed significant part in the feasible removal of harmful metals and antibiotic degradation. In this paper, the hierarchical MoS2 was fabricated with B-rGO sheets using facile and low-cost hydrothermal approach and characterized through XRD, HRSEM, HRTEM, Raman, and UV-DRS. The MoS2/B-rGO nanocomposites exhibit higher photo-responsive region than the visible window. From the UV-DRS studies, the optimized band gap level calculated as 1.7 eV for MoS2/B-rGO this is due to a direct connection between the B-rGO layers would strongly suppress the electron-hole pair recombination. The maximum photocatalytic degradation efficiency of ~85.3% towards Tetracycline hydrochloride (TC) and Cr (VI) to Cr (III) of ~80.1% was achieved. This investigation was likely to be new open window for the development of environmental and energy applications for future generations.

Numerical Modelling and Optimization of Two-Dimensional Phononic Band Gaps in Elastic Metamaterials with Square Inclusions

A numerical simulation study on elastic wave propagation of a phononic composite structure consisting of epoxy and tungsten carbide is presented for low-frequency elastic wave attenuation applications. The calculated dispersion curves of the epoxy/tungsten carbide composite show that the propagation of elastic waves is prohibited inside the periodic structure over a frequency range. To achieve a wide bandgap, the elastic composite structure can be optimized by changing its dimensions and arrangement, including size, number, and rotation angle of square inclusions. The simulation results show that increasing the number of inclusions and the filling fraction of the unit cell significantly broaden the phononic bandgap compared to other geometric tunings. Additionally, a nonmonotonic relationship between the bandwidth and filling fraction of the composite was found, and this relationship results from spacing among inclusions and inclusion sizes causing different effects on Bragg scatterings and localized resonances of elastic waves. Moreover, the calculated transmission spectra of the epoxy/tungsten carbide composite structure verify its low-frequency bandgap behavior.

Effect of volume of the solution and sulfurization on properties of Cu2ZnSnS4 thin films fabricated by spray assisted chemical vapour deposition method

ABSTRACT Cu2ZnSnS4 thin films were produced by spray assisted chemical vapor deposition process (SACVD) technique using different volumes of aqueous ionic solution, followed by sulfurization in sulfur vapors at 500°C and under Argon atmosphere. These CZTS thin films were analysed by X-ray diffraction and Raman scattering analysis that have confirmed the kesterite phase structure of CZTS films before and after sulfurization. The optimum band gap of the as-deposited CZTS films are between 1.40 and 1.43 eV. The cristallinity of the layers improve after sulfurization and their band gap varies between 1.44 and 1.50 eV. The surface morphology of the samples was examined by scanning electron microscopy. The chemical composition was determined by energy dispersive X-ray spectroscopy which shows the formation of Cu poor and Zn rich sulfurized CZTS thin films. Hall Effect measurements revealed that all the films before and after sulfurization are p-type. The sulfurized films obtained in our laboratory have carrier concentrations ranging from 3.1 to 6.8 x 1018 cm-3, a resistivity between 0.199 and 0.262 Ω.cm and mobility between 3.5 and 10.1 cm2/V.s.

Synthesis of Cu<sup>2+</sup> Doped ZnO by the Combination of Sol-Gel-Sonochemical Methods with Duck Egg Albumen as Additive for Photocatalytic Degradation of Methyl Orange

Cu2+ doped ZnO by green synthesis was successfully prepared by using a combination of the Sol-Gel-Sonochemical method. Duck egg albumen was used as an additive, a substitute for chemical additives, such as monoethanolamine (MEA) and diethanolamine (DEA). Zn(CH3COO)2·2H2O was used as a precursor, Cu(CH3COO)2·H2O was used as a dopant source with concentrations of 5 wt.%, and isopropanol was used as the solvent. The addition of albumen variations was 10, 20, 30, 40, and 50 mL. The prepared catalyst was applied for the degradation of the methyl orange dyes by using photosonolysis with variations of the degradation time of methyl orange for 30, 60, 90, 120, 150, 180, and 240 min. FTIR spectra showed stretching at 400–550 cm–1 indicating the presence of Zn–O and Zn–O–Cu metal oxides. The optimum bandgap energy value was 2.82 eV with the addition of 30 mL of albumen. XRD analysis showed the optimum particle size of 16.62–53.21 nm after adding 30 mL of additives. The SEM image showed a spherical shape with an average diameter of 2.7 μm. The optimum percentage of degradation obtained was 94.88%, with the irradiation time under UV light for 210 min.

Impurity photovoltaic and split spectrum for efficiency gain in Cu2ZnSnS4 solar cells

Cu2ZnSnS4 (CZTS) solar cells are potential terawatt scale photovoltaic materials due to optimal bandgap and cost-effective synthesis process. However, it shows low efficiency. We have simulated two avenues of efficiency enhancement in Cu2ZnSnS4 solar cells, viz., impurity photovoltaic, and Split-spectrum strategy. An impurity energy level 0.4 eV above valence band with high electron/hole capture cross-section ratio shows an optimum sub-bandgap absorption of wavelengths up to 1127 nm leading to a short-circuit current (JSC), an observation of beyond Shockley-Queisser (SQ) limit. Secondly, the bandgap tunability of Cu2ZnSnS4 is utilized to design a point focusing spectral splitting system, where we numerically showed an enhancement in efficiency. The spectrum is split into three regions, which are focused on bandgap-matched solar cells to absorb a wider spectrum, and reduced thermalization, transmission losses. A conservative calculation using point-focused spectral splitting shows an efficiency up to 19.4 %, a significant improvement compared to the best-reported efficiency of 12.6 % in the literature.

CdTe-Based Thin Film Solar Cells: Past, Present and Future

CdTe is a very robust and chemically stable material and for this reason its related solar cell thin film photovoltaic technology is now the only thin film technology in the first 10 top producers in the world. CdTe has an optimum band gap for the Schockley-Queisser limit and could deliver very high efficiencies as single junction device of more than 32%, with an open circuit voltage of 1 V and a short circuit current density exceeding 30 mA/cm2. CdTe solar cells were introduced at the beginning of the 70s and they have been studied and implemented particularly in the last 30 years. The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell efficiency of 22.1% and a module efficiency of 19%. In this paper we describe the fabrication process following the history of the solar cell as it was developed in the early years up to the latest development and changes. Moreover the paper also presents future possible alternative absorbers and discusses the only apparently controversial environmental impacts of this fantastic technology.