Effective Mass Ratio Research Articles

Morphology, electrical and linear and nonlinear optical properties of Pb0.85Sn0.15Se thin film

The ternary PbSnSe chalcogenide thin film compounds are promising materials for infrared imaging and semiconducting devices due to their large transparency in infrared regions in this study, we will look to present some physical properties of the ternary Pb0.85Sn0.15Se compound, in order to be able to use it in the optoelectronic application. A thin film of stoichiometric composition Pb0.85 Sn0.15 Se was prepared by thermal evaporation process at a vacuum pressure of 103 Pa. The X-ray and electron diffraction studies revealed that the deposited films are crystalline in nature and belong to a Cubic structure as depicted from the JCPS cards. The surface morphology of the films was examined using the scanning electron microscope. The optical transmission and reflection spectra of the deposited film have been measured in the wavelength spectral range of 200–2500 nm. Therefore, the optical band gap energy and refractive index were evaluated. The dispersion of the refractive index was adequately described using the suggested Wemple – DiDomenico single-oscillator model, whereby the corresponding dispersion parameters, high-frequency dielectric constants besides evaluating the non-linear refractive index, and nonlinear optical susceptibility were evaluated. Further analysis of the refractive index based on the Fan model was also conducted to calculate the carrier concentration to the effective mass ratio. The variation of the conductivity versus temperature was performed and present in the temperature range 293–623 K where the activation energy was calculate.

Propagation of surface plasmons in a quantum collisional semiconductor plasma

In this work, the propagation of surface plasmons in a quantum collisional semiconductor plasma is theoretically investigated using the quantum hydrodynamic model. The general dispersion equation of surface plasmons is deduced and solved in the presence of collisional effects and quantum tunneling of electrons and holes. It is shown that collisions play a significant role in the decay or growth of surface plasmons. Moreover, it is found that the quantum tunneling of electrons and holes increases the phase velocity, the group velocity, and the growth rate of instability. It is also indicated that the growth rate of instability is decreased with the increase of the ratio of hole density to electron density and the ratio of electron effective mass to hole effective mass.

Optimization of operating process was triggered by a saltation of ratio in a full-scale activated sludge system

Chemical additions and energy costs in the wastewater industry are increasing trends in more stringent requirements for effluent quality and electricity rates. A novel ratio of chemical P removal addition to influent total phosphorus (TP) is proposed with an application to optimize operation for saving running costs. For this purpose, we monitored the performance of the process for a consecutive year (2018) and established a dynamic model related to the process. The main process variables included the concentration of influent and effluent quantity, chemical oxygen demand, biochemical oxygen demand, total nitrogen, TP, and dosing chemical additions. The ratio of the average daily effective mass of Fe (MFe-d) to the average daily mass of influent TP (TPInf-Tot-d) was found sharply rise to 3.3 g/g or higher in summer and autumn, whereas it smoothly dropped to about 2.3 g/g in winter and spring. This phenomenon can account for enhanced biological phosphorus removal and upset. The emulating results showed that the proposed indicator can provide a relatively accurate representation of the system dynamics while significantly reducing the chemical additions and energy compared to a model that simulates the entire process without a complicated control system and algorithm.

Effect of substitution doping and surface adsorption of Al atoms on photocatalytic decomposition of water and oxygen from BiVO<sub>4</sub> (010) crystal surface

Using solar photoelectrochemical decomposition of water to produce hydrogen and oxygen is one of the most feasible approaches to obtaining renewable energy. Compared with hydrogen-evolution reaction (HER), the oxygen-evolution reaction (OER) is very complex, there are four sluggish proton-coupled electron transfer processes. It is critical to improve OER performance. The BiVO<sub>4</sub> (010) facet possesses low surface energy, strong visible absorption, and good activity for OER, and is considered as one of the most suitable PEC catalysts. However, its poor electron conductivity, low charge carrier mobility, and high charge recombination rates significantly limit its practical applications. To achieve highly active OER photocatalysts, we modify BiVO<sub>4</sub> (010) facet by substitutial doping with Al atom and surface adsorption with Al atom. According to density functional theory calculations, we compare OER performances of these two modified BiVO<sub>4</sub> (010) facets. The results show that both approaches can effectively regulate the electronic structure of BiVO<sub>4</sub> and then tune OER activity resulting from the change of the structure. Though Al substitutional doping reduces the band gap of the (010) facet and enhances the visible light absorption, the improvement of OER performance is not significant because the doping site is inside and has little influence on the surface active site. Importantly, the surface adsorption of Al atom is considered as an efficient means to improve the OER activity on BiVO<sub>4</sub> (010) facet due to the combined action between surface adsorbed Al and active site Bi atoms. Al adsorbed (010) facet exhibits excellent OER catalytic activity: 1) the induction of localized states and the reduction of band gap are conducive to the electronic transition, optical absorption, thus increasing the electrical conductivity; 2) there is lower hole effective mass, and thus effectively enhancing the ability to transfer from anode surface to electrolyte surface, thereby increasing the difference between the effective mass ratio of electron−hole pairs and 1 and effectively reducing the electron-hole recombination; 3) the nteraction between the active sites and oxygen-containing intermediates is reinforced in the OER process, therefore the potential determining step of OER decreases effectively. This work provides an important reference for designing efficient and stable two-dimensional semiconductor-based photocatalysts for OER. We believe that it will arouse great interest of the BiVO<sub>4</sub> community and motivate numerous experimental researches.

Investigation of structural, optical and electrical properties of PCBM/ZnOEP thin films

In the present work, the spin coating technique was used to prepare the (6, 6)-Phenyl C61 butyric acid methyl ester (PCBM)/Zinc (II) octaethylporphyrin (ZnOEP) thin films by adjusting their relative ratio in blend solutions. X-ray powder diffraction (XRD) patterns assumed growth in the amorphous nature of the films with increasing PCBM concentration. Scanning electron microscopy (SEM) images clearly were showed homogeneous agglomeration. The simultaneous presence of ZnOEP and PCBM Raman modes in the Raman spectrum proved composite production. Values of the indirect-energy band gap were calculated using optical absorption measurements. The disorder in the films affected optical constants, dispersion parameters, and dielectric parameters such as dispersion energy, Ed oscillator energy Eo, plasma frequency ωp, lattice dielectric constant εL, and the carrier concentration to effective mass ratio (N/m*). The change in the charge transfer (CT) of the composite might be due to the presence of PCBM improving the nonlinear optical parameters of PCBM/ZnOEP thin films. Lastly, the dark J-V showed how changing the amount of PCBM could make the current density better. Overall, the findings for PCBM/ZnOEP thin films showed that they offer a new range of potential optoelectronic device applications.

Discovery of Efficient Visible‐light Driven Oxygen Evolution Photocatalysts: Automated High‐Throughput Computational Screening of MA2Z4

AbstractPhotocatalytic oxygen evolution reaction (OER) by 2D semiconductors is a promising strategy for efficient energy conversion. The newly discovered 2D semiconductors MA2Z4 (M = transition metal, e.g., Mo, W; A = C, Si, and Ge; Z = N, P, and As) have shown characteristics of promising photocatalytic OER catalysts. Herein, an automated high‐throughput workflow is proposed to efficiently screen MA2Z4 photocatalytic OER catalysts, and further reveal the theoretical mechanism. The four criteria of semi‐conductivity, bandgap width/band edge position, structural stability, and free energy change, are proposed to screen MA2Z4 catalysts thermodynamically. The exciton properties and carrier mobility of these MA2Z4 are further studied to explore the high‐efficiency photocatalytic OER MA2Z4 with low exciton binding energy and high effective mass ratio. It is found that the bandgap width of MA2Z4 mainly depends on the strength of MZ bonding and the redistribution of electrons, while the catalytic effect is closely related to the adsorption capacity of O atom. In particular, β‐ZrSi2N4 and β‐HfSi2N4 are screened as efficient photocatalytic OER catalysts. This study develops a fully automated method and contributes to a complete framework for screening high‐efficiency photocatalytic OER catalysts.

Generalization on Entropy-Ruled Charge and Energy Transport for Organic Solids and Biomolecular Aggregates.

Herein, a generalized version of the entropy-ruled charge and energy transport mechanism for organic solids and biomolecular aggregates is presented. The effects of thermal disorder and electric field on electronic transport in molecular solids have been quantified by entropy, which eventually varies with respect to the typical disorder (static or dynamic). Based on our previous differential entropy (hs)-driven charge transport method, we explore the nonsteady carrier energy flux principle for soft matter systems from small organic solids to macrobiomolecular aggregates. Through this principle, the synergic nature of charge and energy transport in different organic systems is addressed. In this work, entropy is the key parameter to classify whether the carrier dynamics is in a nonsteady or steady state. Besides that, we also propose the formulation for unifying the hopping and band transport, which provides the relaxation time–hopping rate relation and the relaxation time–effective mass ratio. The calculated disorder drift time (or entropy-weighted carrier drift time) for hole transport in an alkyl-substituted triphenylamine (TPA) molecular device is 9.3 × 10–7 s, which illustrates nuclear dynamics-coupled charge transfer kinetics. The existence of nonequilibrium transport is anticipated while the carrier dynamics is in the nonsteady state, which is further examined from the rate of traversing potential in octupolar molecules. Our entropy-ruled Einstein model connects the adiabatic band and nonadiabatic hopping transport mechanisms. The logarithmic current density at different electric field-assisted site energy differences provides information about the typical transport (whether trap-free diffusion or trap-assisted recombination) in molecular devices, which reflects in the Navamani–Shockley diode equation.

In-plane optical and electrical anisotropy in low-symmetry layered GeS microribbons

Layered group-IV monochalcogenides, including GeS, GeSe, SnS, and SnSe, garner attention because of their anisotropic structures and properties. Here, we report on the growth of GeS microribbons via chemical vapor transport (CVT), which affords each of them with a low-symmetry orthorhombic structure and anisotropic optical and electronic properties. The single-crystalline nature of the GeS microribbon, which has a typical thickness of ~30 nm, is confirmed. Polarized Raman spectra reveal angle-dependent intensities that are attributed to the anisotropic layered structure of GeS microribbons. The photoluminescence (PL) spectra reveal a peak at ~1.66 eV. The angle-dependent PL and anisotropic absorption spectroscopy results provide evidence for a distinct anisotropic optical transition near the energy band edges; this phenomenon is also predicted by our density functional theory (DFT)-based calculations. Strong in-plane direct-current transport anisotropy is observed under dark and white illumination by using back-gate cross-shaped field effect transistors (CSFETs) fabricated with the GeS microribbon; significant gate-tunable conductivity is also confirmed. The strong anisotropy is further confirmed by the DFT-calculated effective mass ratio. Our findings not only support the application of GeS microribbons in anisotropic photoelectronic transistors but also provide more possibilities for other functional device applications.

Static Equivalent Modeling of Dynamic Seismic Forces for Realizing Earthquake-Resistant Spatial Truss Structures

This study deals with spatial truss structures composed of a double layer spatial truss dome and two truss plate-type wall substructures subjected to horizontal earthquake motion. Comparative investigations of the structures are also carried out by considering the structural eccentricity varying the wall height. The equivalent static seismic force, which is hereinafter referred to as the static seismic force, is calculated by the response spectrum method, and the seismic force distribution and response deformation applied on the structure are analyzed and investigated. The elastic seismic response analysis using static seismic force and the influence of eccentricity on seismic response characteristics is carried out. In addition, a method to calculate the static seismic force of medium and medium-sized large-span double-layer truss dome is also proposed by considering the shape, height, span and support conditions of the structure. The purpose of this study is to investigate the effect of the substructure on the seismic static force because the roof truss structure with curved surface has higher stiffness. In addition, the seismic response characteristics of long-span structures are different from those of multi-story structures, which have the structural characteristics of its vertical response as well as horizontal response to horizontal earthquake motion. Based on the elastic seismic response analysis and the static analysis of the static seismic force calculated by the response spectrum method, the seismic force distribution and deformation characteristics of the analysis model with or without eccentricity are analyzed and discussed. It is seen that the static equivalent modeling with the maximum effective mass ratio can be used to obtain the seismic force distribution in this kind of long-span structure.

Applicability of Proportional Damping for Seismic Response Evaluation Using Three-Dimensional Finite Element Method Model Consisting of Structures with Multiple Damping Properties

The purpose of this study is to investigate the applicability of proportional damping to reduce the computational load, which is a common issue for seamless structural integrity evaluation with a 3D-FEM model. When the proportional damping is applied, it is necessary to compare this method with current design method (strain energy proportional damping) regarding on the seismic response calculation precision. Therefore, the research target is to construct a modeling method of proportional damping that realizes the same calculation precision as current design method. The ratios of the maximum stresses in strain energy proportional damping and proportional damping were confirmed using the 3D-FEM model with multiple damping properties, and the applicability of the proportional coefficients setting method based on the magnitude of the effective mass ratio was examined. As a result, it was confirmed that the proportional damping method can calculate the same stress distribution as current design method by setting the proportional coefficients for vibration modes with large effective mass ratios and for the upper limit frequency of the target frequency range.

Influence of the spin-orbit split-off valence band on the hole g factor in semiconductor nanocrystals

We present results of $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ calculations of the effective $g$ factor of holes confined in spherical, cube, and planar semiconductor nanocrystals (NCs). We use the six-band Luttinger model for semiconductors with the zinc-blende crystal structure and study the size dependence of the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ top valence subband hole $g$ factor caused by the admixture of the spin-orbit split-off valence subband ${\mathrm{\ensuremath{\Gamma}}}_{7}$. We present semianalytical expressions for the hole $g$ factor which depends on the light- to heavy-hole effective mass ratio $\ensuremath{\beta}$ and on the ratio between spin-orbit energy splitting of valence band ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}$ and the hole quantization energy ${E}_{h}$. The admixture of ${\mathrm{\ensuremath{\Gamma}}}_{7}$ states is significant for small ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}/{E}_{h}$ and, in spherical and cube NCs, leads to a strong size dependence of the hole $g$ factor. In thin planar nanoplatelets (NPLs) with infinite or large lateral sizes, the dependence of the heavy-hole $g$ factor on NPL thickness is relatively weak. It is drastically enhanced and may become nonmonotonic in NPLs with finite in-plane sizes due to the additional hole states mixing. We discuss our results in comparison with published experimental data for CdSe- and InP-based spherical NCs and NPLs and point out the specificity of extracting hole $g$ factor from the data measured on excitons.

Electronic Coherences Steer the Strong Isotope Effect in the Ultrafast Jahn-Teller Structural Rearrangement of Methane Cation upon Tunnel Ionization.

We report on fully quantum electronic-nuclear dynamics following sudden ionization from the neutral in the three lowest electronic states of the CH4+ and CD4+ cations. There is a strong Jahn-Teller effect in the Franck-Condon region, and we employ two nuclear degrees of freedom that span the internal coordinates involved in the Jahn-Teller coupling. The initial state results from tunneling ionization by a strong IR field which coherently pumps the three lowest states of the cation, D0, D1, and D2. The quantum dynamical simulations show that a strong isotope effect occurs when the ionization significantly accesses the D2 state of the cation in the Franck-Condon region. The computed isotope effect is larger than expected on the basis of the effective mass ratio. The strong effect is due to fast oscillations of the electronic coherences between the D2 and the D1 and D0 electronic states and their modulation by the nonadiabatic couplings before a significant onset of nuclear motion. The magnitude of the effect is similar to the one that we previously reported for a sudden photoionization process. A strong isotope effect has been observed in high harmonic spectroscopy studies of the very short time dynamics Jahn-Teller structural rearrangement of the methane cation upon sudden ionization.

Study of the effect of capping agent variation on P3HT:CdSe hybrid solar cells

We present here a new study on the incorporation of cadmium selenide (CdSe) nanoparticles (NPs) in Poly-3-hexylthiophene (P3HT) polymer matrix. Our aim is to improve the performance of the hybrid solar devices by varying capping agents on top of CdSe NPs for each active layer sample. We investigated the optical properties of differently capped Bulk Heterojunction (BHJ) P3HT:CdSe cells. We extracted the optical constants (refractive index n, extinction coefficient k, real ε′ and imaginary ε′′ parts of dielectric permittivity) from fitted Transmittance T and Reflectance R spectra. Then, we were able to determine the static refractive index ns and permittivity εs, the plasma frequency ωp, the carrier density to effective mass ratio N = me, the optical conductivity roc, the optical band gap Eg and the oscillation and dispersion energies E0 and Ed, using equations proposed by the theoretical models such as Cauchy model, Drude-Lorentz, Tauc model, and Wemple-DiDomenico.

BCS-BEC crossover in a two-band superconductor with odd-parity hybridization

We study the crossover from the weak coupling Bardeen-Cooper-Schrieffer (BCS) state to Bose-Einstein condensation (BEC) at strong coupling in a two-band superconductor with orbitals of opposite parity coexisting at a common Fermi surface in the metallic state. In such systems hybridization can play a role similar to spin-orbit interaction in fermionic spinor gases, enhancing interband pairing and opening the possibility for driving the BCS-BEC crossover. Building on a mean-field analysis, we investigate the BCS-BEC crossover induced by a variation of the hybridization strength. We show that the relevant scale for the crossover depends strongly on the ratio of effective masses, with the crossover favored in systems with one dispersive and one flat band. Including the effect of thermal pair fluctuations in a one-loop approximation, we calculate the dependence of the critical temperature on the microscopic parameters in the strong coupling regime.

Effect of non-annealed and annealed ZnO on the optical properties of PVC/ZnO nanocomposite films

The goal of this study was to investigate the optical properties of the prepared polyvinyl chloride (PVC)/zinc oxide (ZnO) nanocomposite films. The PVC/ZnO nanocomposite films consist of the addition of different concentrations with both non-annealed ZnO nanoparticles and ZnO nanoparticles annealed at temperature of 700°C. The PVC/ZnO nanocomposite films by weight concentrations of (0 wt.%, 2.5 wt.%, 5 wt.% and 10 wt.%) have been prepared by the casting method. The optical absorbance and transmittance values of the composites films were measured in the wavelength range between (250 to 1100 nm) at room temperature by using the UV-1800 Shimadzu spectrophotometer. The optical properties (absorption coefficient, dielectric constant, refractive index, and optical conductivity) have been investigated by the ultraviolet (UV) spectrophotometer. The optical parameters (direct optical energy gap, excitation energy for electronic transitions, the dispersion energy, static refractive index, static dielectric constant, optical oscillator strengths, the moments of optical spectrum, linear optical susceptibility, third-order nonlinear optical susceptibility, nonlinear refractive index, high-frequency dielectric constant, the carrier concentration to the effective mass ratio, the long wavelength refractive index and the plasma frequency) were calculated. The results showed that the optical properties behavior of the PVC/ZnO nanocomposite films was found to be dependent on the ZnO concentration, and photon wavelength. In addition, the results of the study show that the optical parameters can be influenced by alter the concentration of the nonannealed and annealed a ZnO nanoparticle in the PVC polymer matrix.

Effect of local structure on the optical and dielectric behaviour of Sm doped GeSbTe phase change material

Abstract Ge2Sb2Te5 (GST) is considered to be one of the most prominent phase change materials for data storage applications. The UV–Vis–NIR transmittance spectra of (Ge2Sb2Te5)100-xSmx (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) thin films are utilized to analyze the effect of rare earth element Sm on the optical behaviour of GST. The linear and nonlinear optical studies of GST on Sm incorporation provide the understanding of electron transport properties and band structural details. The optical parameters such as absorption coefficient (α) and the refractive index are obtained through transmission data and are analyzed for Sm doped GST thin films. There is significant change of the absorption coefficient near the optical band gap for (Ge2Sb2Te5)100-xSmx thin films. The optical dispersion parameters are analyzed to understand the material's structure. The optical band gap, Urbach energy, and disorder of Sm doped GST thin films are analyzed for band structure modification details on Sm addition. The free career concentration to electron effective mass ratio and high-frequency dielectric constant for (Ge2Sb2Te5)100-xSmx thin films are analyzed. Optical conductivity, dielectric constant, surface and bulk energy loss function and tan δ loss function for (Ge2Sb2Te5)100-xSmx thin films are obtained. The optical non-linear parameters are analyzed to understand the dependence of the polarizability of GST on Sm addition. The incorporation of Sm leads to the change in local bonding environment which may improve the switching mechanism of phase change memory devices.

Pair-correlation functions and density-modulated states in electron–hole bilayer: thermal and mass-asymmetry effects

We have studied the effect of temperature and electron–hole mass-asymmetry on pair-correlation functions (PCFs) of a coupled electron–hole bilayer, treating correlations dynamically using the dynamical self-consistent mean-field approach of Singwi, Tosi, Land, and Sjolander. Taking a fixed electron–hole effective mass ratio $$m_h^*/m_e^*=5$$ , both intra- and interlayer static PCFs are calculated for their dependence on carrier density $$r_{se}$$ , temperature $$\tau _e$$ , and interlayer spacing d. Besides, the static wavevector-dependent density susceptibility is obtained to probe the role of these effects on the hitherto existence of density-modulated phases in the bilayer. We find that thermal effects in overall make correlations weaker, but the mass-asymmetry results in stronger correlations both within and across the layers, with the effect being most pronounced in the holes layer. In the strong coupling regime (i.e., large $$r_{se}/\tau _e d$$ ), the intra- and interlayer PCFs show pronounced in-phase periodic oscillations, typical of a spatially localized phase in the bilayer. Correspondingly, the in-phase component of static density susceptibility is seen to exhibit in the close approach of two layers an apparently diverging peak at a wavevector coincident with the location of sharp peak in the static structure factor, implying the emergence of a density-modulated phase in the bilayer. Parallel to the zero-temperature study, the charge-density-wave (CDW) phase is found to dominate at higher densities, with a cross-over to the Wigner crystal (WC) phase below a critical density. As an interesting result, we find that while thermal effects tend to oppose the formation of density-modulated phase, the electron–hole mass-asymmetry boosted correlations favour it, with the two effects almost cancelling out at $$\tau _e=0.125$$ , thus resulting in the CDW-WC cross-over at nearly the same critical density as for a zero-temperature mass-symmetric electron–hole bilayer. Our prediction of coupled WC phase is found to be in qualitative agreement with path-integral Monte Carlo simulations.

Fabrication and Characterization of Ni-, Co-, and Rb-Incorporated CH3NH3PbI3 Perovskite Solar Cells

Ni- and Co-incorporated CH3NH3PbI3 perovskite solar cells were fabricated and characterized to optimize the photovoltaic and optical properties related to surface morphology, crystal growth and orientation, and electronic structures. Partially replacing Pb with Ni or Co in the perovskite crystals improved the photovoltaic performance and carrier mobility based on the effective mass in the band structure. In particular, the addition of both Ni and Rb compounds to perovskite improved the long-term stability of the photovoltaic cells, which depended on surface modification and coverage, crystal growth, and the high (100) orientation in the perovskite layer. The short-circuit current density of the cells was increased by promoting the generation and mobility of photoinduced carriers, which were inversely proportional to the effective mass ratio. Electron correlation was associated with the promotion of charge transfer owing to the hybridization between the 3d orbitals of Ni and the 5p orbitals of the I atoms near the valence band state.

Optical properties of Al-doped ZnO thin films obtained by the method of high-frequency magnetron sputtering

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index [Formula: see text], absorption coefficient [Formula: see text], extinction coefficient [Formula: see text], dielectric functions [Formula: see text] and optical conductivity [Formula: see text]) of thin films and thickness [Formula: see text] can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Role of intermediate band and carrier mobility in Sn/Fe doped CuAlS2 thin film for solar cell: An ab-initio study

Formation of intermediate band in environmentally stable and wide band gap semiconductor, CuAlS2, have been studied towards potential, low cost and efficient thin film solar cell material. We investigate the effect of sustainable low-cost dopant (Sn and Fe) in CuAlS2 film by means of density functional theory within the modified Becke-Johnson approximation for the calculation of electronic and optical properties. Polar film of CuAlS2 in (001) direction shows lower band gap than the bulk CuAlS2 due to the excess Cu and Al atoms. Doping of Sn and Fe in CuAlS2 form partially filled, isolated intermediate band. Absorption coefficients for Sn and Fe doped films show higher absorption under visible energy region than the pristine bulk and film. Fe and Sn doped films show efficiencies of 34.67 and 35.64%, respectively within spectroscopic limited efficiency. By means of present study, Sn and Fe doping formed intermediate band, improved absorption in visible light and power conversion efficiency. We suggest Sn doped CuAlS2 as the promising material due to higher effective mass ratio of charge carriers, hence lower rate of recombination, indicates improved performance of CuAlS2 based thin film solar cell.