Band Gap Of Cu Research Articles

Tuning the bandgap of Cu(II) phosphinate coordination polymers by ligand selection and coordination geometry

Five coordination polymers, denoted as ICR-15, ICR-16, ICR-17, ICR-18, and ICR-19, were prepared using three previously reported phosphinic acids, namely H2PBP(Me), H2PBP(Ph), H2BBP(Ph), and one new ligand H3TPBTP(Me), in conjunction with Cu2+ cations. These coordination polymers were characterized with single crystal X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermal analysis, and UV–vis spectroscopy. The crystal structures of the coordination polymers were analysed, revealing a variety of coordination environments and distinct structural motifs. Optical band gaps determined from the UV–vis spectra of the coordination polymers range from 2.8 eV to 3.5 eV, corresponding to wide bandgap semiconductors. Interestingly, the coordination geometry of Cu2+ was found to have a negligible influence on the size of the direct or indirect band gap.

N to P-type transition with narrowing optical bandgap and increasing carrier concentration of spin coated Cu doped ZnS thin films for optoelectronic applications

To accomplish the demand of optimized n-type buffer layer in photovoltaic cells; we have studied and analysed various doping compositions of Copper (Cu) into Zinc Sulfide (ZnS) thin films. A series of Cu doped ZnS thin films are fabricated on glass substrate by using spin coating technique at optimized parameters. X-Ray diffraction (XRD) technique revealed that Cu doped ZnS thin films have single phase wurtzite (hexagonal) structure up to 4% doped samples. However, XRD spectra of 6% Cu doped thin films depicted an extra peak of CuS phase that confirmed the secondary phases are formed due to inadequate incorporation of Cu in ZnS structure. Scanning electron microscope (SEM) images showed that the fabricated thin films are compact, dense and homogeneous without voids and cracks on the surface. Energy dispersive X-ray (EDX) analysis indicated that stoichiometric ratio of Zinc to Sulfur is maintained except for 6% Cu doped concentration. Fourier transform infra-red (FTIR) absorption spectrum of thin films series confirmed the presence of ZnS vibrational bonds along with vibrational and stretching bonds of carbon, oxygen and hydrogen at appropriate positions. Cu doped thin films from 0% to 4% exhibited n-type character, while 6% Cu doped ZnS sample unveiled p-type nature may be due to CuS secondary phase's formation. UV–Vis optical spectroscopy revealed that the energy band gap also decreased from 3.64 eV to 3.24 eV with varying Cu concentration from 0% to 6% doped ZnS thin films. The energy band gap of Cu doped ZnS is decreased may be due to the existence of Cu-3d state in the upper part of the valence band.

Surface morphology, optical band gap and magnetic behavior of Cu(1-x)MnxFe2O4 nanofibers prepared by sol-gel electrospinning

Novel manganese-substituted copper ferrite (Cu(1−x)MnxFe2O4; x = 0, 0.25, 0.5, and 0.75) nanofibers has been prepared via sol-gel electrospinning technique. The structural, chemical, morphological, elemental, optical and magnetic characteristics of the fibers were investigated. XRD analysis revealed that tetragonal phase of ferrites with impurity phases (CuO, α-Fe2O3 and α-MnO2) was formed. The Williamson–Hall approach indicated that the average crystallite size and lattice strain of the samples were changed by Mn incorporation and then FTIR spectroscopy confirms the characteristic vibration modes of ferrites atoms at tetrahedral and octahedral sites. Field emission scanning electron microscopy (FESEM) emphasized that Cu(1−x)MnxFe2O4 nanofibers were fabricated with some special morphologies after Mn ions incorporation, nanowebs (x = 0.25), beaded nanofibers (x = 0.5), and coarse nanofibers (x = 0.75) with average diameters in the range of 63–93 nm. EDS spectroscopy confirmed the presence of Fe, O, Cu and Mn elements and indicated that the atomic ratio of the elements was close to the nominal values in the initial sols. It was found that the optical band gap of Cu(1−x)MnxFe2O4 changes by Mn incorporation, ranging from 1.5 to 1.8 eV. VSM analysis at room temperature showed normal ferromagnetic behavior of ferrites but a large coercivity (3.11 kOe) is observed for Cu0.25Mn0.75Fe2O4 nanofibers. The saturation magnetization enhanced by Mn incorporation up to x = 0.5 (Ms = 28.7 emu/g).

A high-performance fluorescent probe for detection of cysteine in plasma constructed by combining Cu(I) and 2,5-dimercapto-1,3,4-thiadiazole

A high-performance fluorescent probe 2,5-dimercapto-1,3,4-thiadiazole copper nanoparticles (DMTD-CuNPs) was synthesized by hydrothermal method based on monovalent copper (Cu(I)) and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), and it can effectively detect cysteine (Cys) in plasma. Experiments show that DMTD can reduces band gap of Cu(I) in DMTD-CuNPs, promote charge transfer transition from DMTD to Cu(I) and significantly enhance fluorescence intensity of DMTD-CuNPs at 515 nm. The large Stokes shift of DMTD-CuNPs is 315 nm, which can reduce the self-quenching of probe fluorescence and improves detection accuracy of the probe. In the presence of Cys, fluorescence of DMTD-CuNPs at 515 nm is significantly quenched because Cys reacts with Cu(I) in DMTD-CuNPs through Cu-S bond to form reduced charge transfer, which can be successfully used for the detection of Cys. Linear range and detection limit for Cys detection are 25–65 µM and 50 nM, respectively. Furthermore, feasibility of detecting Cys in plasma using DMTD-CuNPs probe was evaluated by standard addition method, and the absolute recovery is 96–99%. Such a DMTD-CuNPs probe shows high sensitivity, good selectivity and low detection limit for Cys, which is expected to be used for the practical analysis of Cys in plasma.

Tuning Structural and Optical Properties of Porphyrin-based Hydrogen-Bonded Organic Frameworks by Metal Insertion.

Herein, a simple way of tuning the optical and structural properties of porphyrin-based hydrogen-bonded organic frameworks (HOFs) is reported. By inserting transition metal ions into the porphyrin cores of GTUB-5 (p-H8 -TPPA (5,10,15,20-Tetrakis[p-phenylphosphonic acid] HOF), the authors show that it is possible to generate HOFs with different band gaps, photoluminescence (PL) life times, and textural properties. The band gaps of the resulting HOFs (viz., Cu-, Ni-, Pd-, and Zn-GTUB-5) are measured by diffuse reflectance and PL spectroscopy, as well as calculated via DFT, and the PL lifetimes are measured. Across the series, the band gaps vary over a narrow range from 1.37 to 1.62 eV, while the PL lifetimes vary over a wide range from 2.3 to 83 ns. These differences ultimately arise from metal-induced structural changes, viz., changes in the metal-to-nitrogen distances, number of hydrogen bonds, and pore volumes. DFT reveals that the band gaps of Cu-, Zn-, and Pd- GTUB-5 are governed by highest occupied/lowest unoccupied crystal orbitals (HOCO/LUCO) composed of π- orbitals on the porphyrin linkers, while that of Ni-GTUB-5 is governed by a HOCO and LUCO composed of Ni dorbitals. Overall, our findings show that metal-insertion can be used to optimize HOFs for optoelectronics and small-molecule capture applications.

Energy band reconstruction mechanism of Cl-doped Cu2O and photocatalytic degradation pathway for levofloxacin

Cl-doped Cu 2 O microparticles were prepared by hydrothermal synthesis . XRD, BET, SEM, TEM, UV–Vis and RSM were used to reveal the microstructure, optical properties and degradation regularity of the Cl-doped Cu 2 O microparticles. The band gap structures and state densities of Cl-doped Cu 2 O microparticles were computed based on density functional theory . The major intermediate degradation products and potential photocatalytic degradation pathways of levofloxacin were identified by HPLC–MS/MS. The photocatalytic active sites of levofloxacin and its intermediate products were calculated based on the frontier electron densities. The results showed that the prepared Cl-doped Cu 2 O microparticles increased the specific surface area and absorption efficiency of visible light compared with undoped pure Cu 2 O. The doping of Cl introduced hybrid orbitals and oxygen vacancy defects in the Cu 2 O crystal cell and decreased the forbidden bandwidth of Cu 2 O crystal microparticles, leading to a redshift of the absorption edge . Cl doping could form a shallow donor impurity energy level composed of Cl 3 p orbital in the energy gap of Cu 2 O and make the energy band denser and move to a lower energy, which could promote the electron leap to the conduction band through the impurity level . The doping of Cl can make the density of states curve of the Cu 2 O crystal shift to low-energy and the Cl-doped Cu 2 O rendered to half-metallic behavior and characteristic behavior of an n type semiconductor. The photocatalytic degradation of levofloxacin was attributed to attack of photogenerated holes and hydroxyl radicals , and the ring opening of the piperazine ring by oxidation and decarboxylation reactions from the quinolone ring might be two photocatalytic degradation pathways. This study revealed the mechanism of oxygen vacancy formation and the change rules of the band structure by doping of the nonmetal chlorine into Cu 2 O crystallites . • Migration laws of band structure and state density of Cl-doped Cu 2 O were revealed. • Doping of Cl introduced hybrid orbitals and oxygen vacancies in the Cu 2 O crystal. • Doping of Cl decreased band gap of Cu 2 O and led to red shift of absorption edge. • Holes and hydroxyl radicals are the main photocatalytic active species. • Degradation paths of levofloxacin were piperazine ring opening and decarboxylation.

The impact of Ga and S concentration and gradient in Cu(In,Ga)(Se,S)2 solar cells

As one of the leading photovoltaic materials, Cu(In,Ga)(Se,S)2 has two distinct advantages over other candidates. First, its conduction band and valence band could be independently tuned by adjusting the Ga/(Ga + In) and S/(S + Se), respectively. Next, its composition distribution could be feasibly tuned by controlling the thin film deposition process. These merits have been utilized in fabricating the Cu(In,Ga)(Se,S)2 solar cells with world record efficiency. However, these features have not yet been satisfactorily simulated. In order to understand the mechanism of high-performance Cu(In,Ga)(Se,S)2 solar cells, we obtained the tunable bandgap of absorber layer and suitable conduction band offset between absorber layer and buffer layer via Ga and S concentration and gradient, by combining both first-principle calculations and numerical simulations with Poisson equation and the continuity equation. In particular, compared with other photovoltaic materials, the bandgap of Cu(In,Ga)(Se,S)2 could be tuned flexibly across the layer thickness to realize spatial energy band optimization with double-concentration-grading absorber. The efficiency of 23.29% was obtained based on theoretical calculations and numerical simulations, which is almost the same as the reported result, in the considerations of (i) optimum bandgap of absorber, (ii) band energy offset, (iii) double (Ga- and S-) concentration grading, and (iv) low defect density in the absorber layer. In addition, we obtained a Cu(In,Ga)(Se,S)2 solar cell with a high S content uniform band gap efficiency of 23.53%. Therefore, we provided an understanding for tunable engineered band energy research in high-efficient Cu(In,Ga)(Se,S)2 solar cells.

Growth, crystal structure and temperature dependence of the band gap of Cu-=SUB=-2-=/SUB=-ZnGeS-=SUB=-4-=/SUB=- single crystals

Cu2ZnGeS4 single crystals were grown by chemical vapor transport reaction method. Their composition and crystal structure were determined. It was shown that the obtained single crystals crystallize in a tetragonal structure. The band gap of the obtained single crystals was determined basing on transmission spectrum in the region of the absorption edge in temperature range of 10-320 K. It was found that band gap width increases with decreasing of temperature. Keywords: Bridgman method, single crystals, crystal structure, transmission spectrum, band gap.

Structural Characteristics and Photoluminescence of Thin Films of Cu(In1–xgax)(Syse1–y)2 Solid Solutions

The phase composition and structural and optical characteristics of thin films of Cu(In1–xGax)(SySe1–y)2 solid solutions with the chalcopyrite structure were investigated. The unit-cell constants according to x-ray diffraction analysis were a ~ 5.720 A and c ~ 11.52 A. The elemental compositions were x = Ga/(Ga + In) ~ 0.14 and y = S/(S + Se) ~ 0.11 for Cu(In1–xGax)(S ySe1–y)2 thin films. The optical band gap of Cu(In1–xGax)(S ySe1–y)2 solid solutions determined from measurements of photoluminescence spectra and luminescence excitation spectra at ~4.2 K was Eg ~ 1.122 eV. The mechanism of radiative recombination of nonequilibrium charge carriers in thin films of Cu(In1–xGax) (S ySe1–y)2 solid solutions is discussed.

Structure prediction of CuBiI ternary compound and first-principles study of photoelectric properties

Ternary metal halides have attracted much attention as a new potential photoelectric material due to their ultra-high photoelectric conversion efficiencies. In this paper, USPEX, a crystal structure prediction software based on genetic algorithm, is used to investigate the potential crystal structures of ternary CuBiI compounds (CuBi<sub>2</sub>I<sub>7</sub>, Cu<sub>2</sub>BiI<sub>5</sub>, Cu<sub>2</sub>BiI<sub>7</sub>,Cu<sub>3</sub>BiI<sub>6</sub>, Cu<sub>3</sub>Bi<sub>2</sub>I<sub>9</sub>, CuBi<sub>3</sub>I<sub>10</sub>, and Cu<sub>4</sub>BiI<sub>7</sub>) at atmospheric pressure and absolute zero temperature. Based on the density functional theory, the formation energies, elastic coefficients, and phonon dispersion curves of the predicted structures are calculated. The twelve stable CuBiI compounds with good thermodynamic, dynamical and mechanical stabilities are identified. The twelve crystal structures of CuBiI compound feature mainly the co-existence of Cu—I and Bi—I bonds and coordination polyhedrons of I atoms. The band gaps of twelve structures, calculated by HSE06 method, are 1.13–3.09 eV, indicating that the stoichiometric ratio affects the band gap obviously. Among them, the band gaps of Cu<sub>2</sub>BiI<sub>5</sub>-<i>P</i>1, Cu<sub>2</sub>BiI<sub>7</sub>-<i>P</i>1 and Cu<sub>2</sub>BiI<sub>7</sub>-<i>P</i>1-II are relatively small, close to the optimal band gap value for light absorption (1.40 eV), demonstrating that these compounds are suitable for serving as light absorbing materials in solar cells. The distribution of density of state (DOS) indicates that the top of the valence band of CuBiI compound is attributed to the hybridized Cu-3d and I-5p orbitals; the bottom of the conduction band of Cu<sub>3</sub>BiI<sub>6</sub>-<i>R</i>3 comes mainly from the Bi-6p and I-5p orbitals, and Cu-3d contributes little; the conduction band bottom of Cu<sub>2</sub>BiI<sub>7</sub> is mainly from the I-5p orbital, and the Cu-3d has little contribution. The bottoms of the conduction band of other structures originate mainly from the hybridized Bi-6p and I-5p orbitals. Electronic localization function and Bader charge analysis show that the Cu—I and Bi—I bonds have more ionic features and less covalent natures. The DOS distribution also confirms the covalent interaction of Cu/Bi-I. In addition, the CuBiI ternary compounds have extremely strong light absorption capacities (light absorption coefficient higher than 4 × 10<sup>5</sup> cm<sup>–1</sup>) in the high-energy region of visible light and high power conversion efficiency (31.63%), indicating that the CuBiI ternary compounds have the potential to be an excellent photoelectric absorption material. Our investigation suggests the further study and potential applications of CuBiI ternary compound as absorber materials in solar cell.

Излучательная рекомбинация на ионно-индуцированных дефектах в тонких пленках твердых растворов Cu(In, Ga)Se-=SUB=-2-=/SUB=-

In thin films of Cu(In,Ga)Se2 solid solutions radiation-induced effects after irradiation of hydrogen ions with an energy of 2.5, 5 and 10 keV with dose of ~ 3∙10^15 cm-2 were studied. A comparative analysis of the optical characteristics of non-implanted and implanted Cu(In,Ga)Se2 thin films was carried out based on the measurements of photoluminescence spectra and the luminescence excitation spectra at liquid helium temperature of ~ 4.2 K. The bandgap of Cu(In,Ga)Se2 solid solutions determined from the data of mathematical processing of the luminescence excitation spectra was ~ 1.171 eV. An intense band with a maximum of ~ 1.089 eV was found in the photoluminescence spectra of non-implanted and hydrogen-implanted Cu(In,Ga)Se2 thin films caused by the recombination of free electrons with holes localized in the tails of the valence band. It was established that appearance of intense broad bands in the photoluminescence spectra with maxima in the energy range of ~ 0.92 eV and ~ 0.77 eV is due to radiative recombination of nonequilibrium charge carriers at deep energy levels of acceptor type ion-induced defects formed in the bandgap of Cu(In,Ga)Se2 solid solutions. The conditions for the appearance of the ionic passivation effect of dangling electronic bonds on the surface and in the bulk of Cu(In,Ga)Se2 polycrystalline films, possible nature of point defects in the structure and the mechanisms of radiative recombination are discussed.

The role of process temperature on structural, optical, vibrational and electronic environments of thermal chemical vapor-deposited copper-doped zinc oxide nanostructured thin films

Copper incorporated zinc oxide (Cu–ZnO) nanostructure thin films were deposited by using a high-temperature chemical vapor deposition technique at 650–800 °C with Cu and Zn powder in O2 and N2 gas atmosphere. The Cu–ZnO thin films were characterized by AFM, XRD, FTIR, Raman spectroscopy, UV–Vis spectroscopy, and XPS to investigate the structural, vibrational, optical, and electronic environments of Cu–ZnO thin films. The AFM study revealed that nanoparticles of Cu–ZnO films are varied from 225 to 74 nm with increasing process temperature from 650 to 800 °C. The relative intensity of E2(high) phonon increases with increase in the process temperature 650–800 °C. The photoluminescence spectra of Cu-doped ZnO films showed a strong orange emission peak centered at 635.12 nm and 700.06 nm due to bound excitation and intrinsic defects, respectively. The Tauc optical bandgap of Cu–ZnO thin films decreased from 2.72 to 2.22 eV, due to the increase with an increase in copper doping concentration. Moreover, the semiempirical electronic environments of Zn 2p3/2, O(1 s), and Cu (2p) core orbital are analyzed by the Origin software.

Visible light sensitive Cu doped ZnO: Facile synthesis, characterization and high photocatalytic response

The different concentrations of 0.0, 1.0, 2.5 and 5.0 wt% Cu-doped ZnO (Cu@ZnO) nanoparticles (NPs) have been synthesized for opto-photocatalytic applications by a facile and cost-effective route. The formation and structural analyses of Cu@ZnO NPs was recognized by X-ray diffraction (XRD), Fourier transform (FT)-Raman and Transmission electron microscopy (TEM). The average crystallite size of 28.9, 27.4 and 26.4 nm was calculated for (101) intense peak and found to be decreased with increasing the contents of Cu. The residual microstrain values are noted ~3.84 × 10−3, 4.03 × 10−3 and 4.19 × 10−3. The particle size of 170, 109, 127 and 175 nm is obtained for undoped and Cu doped ZnO NPs from FESEM. The optical band gap of Cu@ ZnO NPs were estimated through Kubelka-Munk theory and noted ~3.225, 3.150, 3.100 and 2.995 eV for 0.0, 1.0, 2.5 and 5.0 wt% Cu@ZnO NPs; this shows decreases with increasing the Cu contests in ZnO lattice. Photoluminescence (PL) spectra of Cu@ZnO NPs shows near band edge emission at 407–411 nm with emission band 565-572 nm correspond to intrinsic defects in ZnO lattice. The photocatalytic performance of Cu@ZnO NPs was assessed through decolourizing of methyl green beneath the visible light illumination (λ = 425–460 nm). Photocatalytic action of Cu@ZnO samples was 3.5 times greater to neat ZnO. Photocatalytic properties of Cu@ZnO NPs can be used for water purification in environmental applications.

Photocatalytic water splitting properties of Cu2+ exchanged Beta zeolites

Photocatalytic water splitting with solar energy is the most promising and environmentally friendly hydrogen production method. Having an efficient and cost-effective photocatalyst is key to hydrogen production. Cu dopant has been shown to greatly enhance photocatalytic activities. In this work, Cu2+ ions were doped into Beta zeolite powders (Cu–Beta) by the ion exchange method. The hydrogen evolution efficiency of Cu–Beta was much higher than the raw Beta zeolites without Cu loading. After solid phase reaction, the band gap of Cu–Beta reduced from 3.48 eV to less than 2 eV, and as a result enhanced the optical absorption intensity, particularly in the visible region. The best hydrogen evolution efficiency was 102.12 μmol · g−1 · h−1 when the treated temperature was 900 °C (Cu–Beta–900). The temperature of the solid phase reaction had an important influence on the photocatalytic performance of Cu–Beta; a suitable reaction temperature can greatly improve its photocatalytic performance.

Cu(In,Al)Se2 Photovoltaic Thin Film Solar Cell from Electrodeposited Stacked Metallic Layers

An improved technique for synthesis of Cu(In,Al)Se2 is demonstrated, associated with sequential electrodeposition of a stacked layer in the order of Cu/Al/In followed by annealing in selenium vapor. Many advantages such as adjustable constitutes composition, good polycrystalline structure, pure chalcopyrite phase, uniform and compact surface morphology are obtained compared to the film fabricated by conventional electrodeposition process. The film thickness and the concentration of each metal deposited were controlled by the flexibility parameters of deposition time. The influence of Al content on the crystal structure, surface morphology, photoelectrochemical performance, optical and electronic properties of the films were investigated. The crystal size decrease and the energy bandgap of Cu(In,Al)Se2 thin film increase gradually with the increasing Al were revealed. Impedance potential test reveals the manufactured Cu(In,Al)Se2 thin films are all p-type semiconductor and the carrier concentration increases with the Cu/(Al + In) and Al/(In + Al) ratio. Photoelectrochemical investigation of Cu(In,Al)Se2 films verified that a higher photocurrent was obtained with a relative lower Al content due to a narrower bandgap leading to lower-energy photon absorption and a lower carrier density and a larger grain size both benefitting the transfer of photogenerated carriers and decrease the recombination of charge carriers. The obtained optimum Cu(In,Al)Se2 thin film based solar cell has been theoretical modeling and simulated. A high PCE of 17.08% was gained implying its potential application in photovoltaic devices.

Radiative Recombination in the Cu(In,Ga)Se2 Thin Films Irradiated with Hydrogen Ions

The irradiation-induced effects in Cu(In,Ca)Se2 thin films after irradiation with hydrogen ions with dose of [Formula: see text][Formula: see text]cm[Formula: see text] and different energies in the range of 2.5–10[Formula: see text]keV were studied. Irradiated and nonirradiated thin films were investigated by low-temperature (4.2[Formula: see text]K) photoluminescence and photoluminescence excitation methods. The appearance of intense bands at [Formula: see text][Formula: see text]eV and 0.77[Formula: see text]eV in the photoluminescence spectra may be related to radiative recombination on the irradiation-induced defects with deep energy levels in the bandgap of Cu(In,Ca)Se2 solid solutions. A possible nature of these defects and process of radiative recombination are discussed.

Unveiling the dual role of chemically synthesized copper doped zinc oxide for resistive switching applications

In this study, efforts were devoted to unveiling the dual role of single crystalline Cu (5%) doped ZnO (Cu:ZnO) synthesized by a simple and low-cost chemical process and to investigate its efficacy on resistive switching (RS) applications. It was found that when Cu:ZnO was annealed at a lower temperature of 450 °C and integrated onto ITO/glass for RS applications, only oxygen mediated vacancies were responsible for its resistive switching. However, ferroelectric properties have been observed when the same Cu:ZnO was annealed at a higher temperature of 800 °C and integrated onto Nb doped SrTiO3. X-ray diffraction, high resolution transmission electron microscope, x-ray photoelectron spectroscopy, UV-VIS-near infrared spectrometer, and piezoelectric force microscopy (PFM) were employed to study the crystallinity, interfaces, chemical compositions, bandgap, and domains in Cu:ZnO thin films, respectively. The bandgap of Cu:ZnO was found to be 3.20 eV. PFM study exhibits the domain inversion with 180° polarization inversion by applying an external bias, evidencing its effectiveness for memory applications. When the electrical characteristics were concerned, the RS device based on this ferroelectric Cu:ZnO offers better performance, such as lower SET/RESET voltages (∼1.40 V), higher retention (up to 106 s) without distortion, and higher ON/OFF ratio (2.20 × 103), as compared to the former lower temperature annealed Cu:ZnO devices. A band-diagram was proposed, and transport studies were developed to understand the operational mechanism of these devices. This study explains both the limits and scopes of Cu:ZnO RS devices and formulates an idea which may accelerate the design of future generation devices.

Refractive indices of layers and optical simulations of Cu(In,Ga)Se2 solar cells

Cu(In,Ga)Se2-based solar cells have reached efficiencies close to 23%. Further knowledge-driven improvements require accurate determination of the material properties. Here, we present refractive indices for all layers in Cu(In,Ga)Se2 solar cells with high efficiency. The optical bandgap of Cu(In,Ga)Se2 does not depend on the Cu content in the explored composition range, while the absorption coefficient value is primarily determined by the Cu content. An expression for the absorption spectrum is proposed, with Ga and Cu compositions as parameters. This set of parameters allows accurate device simulations to understand remaining absorption and carrier collection losses and develop strategies to improve performances.

First Principles Study of Electronic and Optical Properties of Pristine and X (Cu, Ag And Au) Doped BiOBr

The electronic structures and optical properties of pristine BiOBr and Cu, Ag and Au doped BiOBr have been analyzed by using a standard density functional theory based ab-initio approach employing generalized gradient approximation through revised Perdew Burke Ernzerhoff type parameterization. The calculation shows that both the doped and pristine BiOBr have indirect band gap, the band gap of the pristine BiOBr found 2.22eV, whereas band gap significantly reduced after doping Cu, Ag and Au on BiOBr. The band gap of Cu, Ag and Au doped BiOBr are 1.2eV, 0.9eV and 1.76eV respectively. The optical properties have been studied through dielectric function, both pure and doped BiOBr shows anisotropic nature. Journal of Institute of Science and TechnologyVolume 22, Issue 2, January 2018, page: 63-69

Investigating sulfur distribution and corresponding bandgap grading in Cu(In,Ga)(S,Se)2 absorber layers processed by fast atmospheric chalcogenization of metal precursors

A remarkable discrepancy between the optically active bandgap of Cu(In,Ga)(S,Se)2 absorber layers for thin film solar cells and the minimum bandgap as determined via elemental depth profiling has been observed in this study. This behavior occurs in absorbers sequentially grown by sulfurization after selenization of metal precursors and is demonstrated and explored in the following, using glow discharge optical emission spectroscopy, external quantum efficiency and Raman scattering. Furthermore this mismatch is explained by investigating the microscopic elemental distributions using transmission electron microscopy. It turns out, that sulfur is - on a microscopic scale - inhomogeneously distributed in the bulk of the absorber and solely present in areas near the absorber surface itself and at inner surfaces, e.g. in voids in the bulk.