eV For Conduction Research Articles

A qualitative study of SnSe thin film solar cells using SCAPS 1D and comparison with experimental results: A pathway towards 22.69% efficiency

We simulated a tin selenide (SnSe) based solar cell device in a standard planar substrate configuration (glass/Mo/SnSe/CdS/i-ZnO/AZO/Al) using a Solar Cell Capacitance Simulator (SCAPS-1D) software to elucidate a path to higher power conversion efficiency (PCE). A baseline model for the device was simulated and established using the experimental results of our recent study on a 2.51% device. A stepwise fitting procedure observed a higher effective density of states in SnSe, along with a band offset of −0.11 eV for conduction between SnSe and CdS; these factors are responsible for limiting the open-circuit voltage ( V OC ). We optimized the buffer and absorber layer parameters to improve the working capabilities to achieve higher efficiency by improving V OC . In particular, the effects of carrier concentration, absorber–buffer interface recombination, absorber thickness, buffer layer thickness, and defect densities were studied and analyzed in detail via simulation. Interestingly, optimal absorber and buffer layer thicknesses of 1.2 μm and 60 nm were obtained for the baseline and simulated devices. Finally, a NiO back-surface field (BSF) layer was introduced, and its performance was evaluated. Significant improvements in V OC and fill factor (FF) were observed with implementing the NiO BSF layer at the SnSe/CdS interface. The optimal device without a BSF layer exhibited a maximum efficiency of 13.79% with a V OC of 0.590 V; a short-circuit current density ( J SC ) of 36.28 mA cm −2 , and an FF of 64.33%. Finally, the highest PCE of 22.69% with a V OC of 0.818 V, J SC of 33.65 mA cm −2 , and FF of 82.41% was observed after applying the BSF layer. • Simulation of SnSe/CdS-based solar cells using experimental results. • Role of NiO BSF in SnSe/CdS planar heterojunction solar cells. • Importance of VB and CB eDOS to enhance the solar cell performance. • Improvement in the fill factor and open-circuit voltage by introducing a NiO BSF layer.

Mechanochemical synthesis of Li-argyrodite Li6PS5X (X = Cl, Br, I) as sulfur-based solid electrolytes for all solid state batteries application

Highly ion-conductive Li6PS5X (X=Cl, Br, I) Li-argyrodites were prepared through a high‐energy ball milling. Electrical and electrochemical properties were investigated. Ball-milled compounds exhibit a high conductivity between 2 and 7×10−4S/cm with an activation energy of 0.3–0.4eV for conduction. These attractive properties were attributed to the spontaneous formation of crystallized Li-argyrodite during ball-milling. An optimization of milling time led to a conductivity of 1.33×10−3S/cm for the Li6PS5Cl phase with an electrochemical stability up to 7V vs. lithium. An all solid state LiCoO2/Elec./In lithium ion battery using ball-milled Li6PS5Cl as electrolyte was successfully assembled, and its room temperature performance is reported.

Size-dependent electroluminescence from Si quantum dots embedded in amorphous SiC matrix

Si quantum dots (QDs) were formed by thermal annealing the hydrogenated amorphous silicon carbide films (a-SiCx:H) with different C/Si ratio x, which were controlled by using a different gas ratio R of methane to silane during the deposition process. By adjusting x and post annealing temperature, the QD size can be changed from 1.4 to 4.2 nm accordingly, which was verified by the Raman spectra and transmission electron microscopy images. Size-dependent electroluminescence (EL) was observed, and the EL intensity was higher for the sample containing small-sized Si QDs due to the quantum confinement effect (QCE). The EL peak energy as a function of the Si QDs size was in good agreement with a modified effective mass approximation (EMA) model. The calculated finite barrier potential of the Si QDs embedded in SiC matrix is 0.4 and 0.8 eV for conduction and valence band, respectively. Moreover, the current-voltage properties and the linear relationship between the integrated EL intensity and injection current indicate that the carrier transport is dominated by Fowler–Nordheim tunneling and the EL mechanism is originated from the bipolar recombination of electron-hole pairs at Si QDs. Our results demonstrate Si QDs embedded in amorphous SiC matrix has the potential application in Si-based light emitting devices and the third-generation solar cells.

Optical excitations inSr2CuO3

We investigated excitation spectra of the one-dimensional chain compound ${\text{Sr}}_{2}{\text{CuO}}_{3}$. The small peak at 2.3 eV in the loss function turned out to correspond to the strong charge-transfer transition at 1.8 eV in conductivity. It has the excitonic character expected in one-dimensional extended Hubbard model of the transition from the lower Hubbard band to the Zhang-Rice singlet state. The strongest peak at 2.7 eV in the loss function is attributed to the continuum excitation of the excitonic charge-transfer transition. The spectral weight sum rule is satisfied within these transitions.

Transport and Phase Transition Characteristics in AgI : Al2 O 3 Composite Electrolytes Evidence for a Highly Conducting 7‐Layer AgI Polytype

The extreme conductivity enhancement (by a factor of up to ) in composites as well as the anomalous phase transition to the α‐phase with a large hysteresis of 50°C was confirmed by conductivity, differential scanning calorimetry, and in situ X‐ray diffractometry (XRD). All the composites exhibited an activation energy of 0.29 ± 0.02 eV in conductivity which was identified with the migration enthalpy for transport in the disordered close‐packed layers in AgI system. A close examination of the XRD patterns shows the existence of a seven‐layer polytype (7H) for AgI with the stacking sequence ABCBCAC. This may account for anomalies in the composites in contrast to the ideal space charge effect in and composites. Since the stacking arrangement can be regarded as a heterostructure of β‐AgI (ABABAB…) and γ‐AgI (ABCABC…) with a sub‐Debye length spacing, the conductivity enhancement may be attributed to the mesoscopic multiphase effect predicted earlier. The hysteresis can be attributed to the elastic effects in the martensitic transformation between α‐AgI and 7H‐AgI. © 2000 The Electrochemical Society. All rights reserved.

Electrical conduction in CaF2 and CaF2-Al2O3 nanocomposite films on Al2O3 substrates

Thin films of pure CaF2 and nanocomposite mixtures of Al2O3 with CaF2 were evaporated on Al2O3 substrates. Interdigital electrodes on some of the substrates allowed in situ measurements of the electrical conduction in the films during and subsequent to film growth. Electrical conduction was studied as a function of film thickness, film deposition rate, composition, time, and temperature. The electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF2 conductivity (i.e., value at more than 50 nm distance) by as much as a factor of 6700 at 200 °C. The high conductivity is characterized by an activation energy of 0.6±0.1 eV, which is significantly lower than the activation energy of about 1.0 eV for conduction in the bulk. However, this high conductivity is thermally unstable and diminishes in time. A high but stable conductivity was obtained in CaF2 films containing about 10 mol % Al2O3 as a dispersed second phase. At 200 °C, a two-phase film gave a factor of 360 enhancement over the measured bulk CaF2 conductivity and a factor of 7 improvement over the best previously reported conductivity for CaF2-Al2O3 composite materials. The origin of enhanced conduction in CaF2 is attributed to ion transport along dislocations. Dislocations anneal with a characteristic log of time dependence that is recognizable in the annealing behavior of the electrical conductivity. Presumably, the addition of a dispersed second phase of Al2O3 to CaF2 serves both to generate and to pin dislocations; the electrical conductance is thereby enhanced and stabilized.

Ionic Conduction Mechanisms in CaF2 and CaF2-Al2O3 Nanocomposite Films on Al2O3 Substrates

ABSTRACTThin films of pure CaF2 and nanocomposite mixtures of Al2O3 with CaF2 were sublimated on Al2O3 substrates. Interdigital electrodes allowed in situ measurements of the electrical conduction of films as a function of thickness, deposition rate, composition, time, and temperature. The electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF2 conductivity (i.e., value at more than 50 nm distance) by as much as a factor of 6700 at 200°C. The high conductivity is characterized by an activation energy of 0.6 ± 0.1 eV, which is significantly lower than the activation energy of about 1.0 eV for conduction in the bulk. However, this high conductivity is thermally unstable and diminishes in time. A high but stable conductivity was obtained in CaF2 films containing about 10 mole percent Al2O3 as a dispersed second phase. At 200°C, a 2-phase film gave a factor of 360 enhancement over the measured bulk CaF2 conductivity and a factor of 7 improvement over the best previously reported conductivity for CaF2-Al203 composite materials. The origin of enhanced conduction in CaF2 is attributed to ion transport along dislocations. Dislocations anneal with a characteristic log of time dependence that is recognizable in the annealing behavior of the electrical conductivity. Presumably, the addition of a dispersed second phase of Al2O3 to CaF2 serves both to generate and to pin dislocations; the electrical conductance is thereby enhanced and stabilized.

Characterization of boron carbide thin films fabricated by plasma enhanced chemical vapor deposition from boranes

We have fabricated boron carbide thin films on Si(111) and other substrates by plasma-enhanced chemical-vapor deposition (PECVD). The PECVD of boron carbides from nido-cage boranes, specially nido-pentaborane(9) (B5H9), and methane (CH4) is demonstrated. The band gap is closely correlated with the boron to carbon ratio and can range from 0.77 to 1.80 eV and is consistent with the thermal activation barrier of 1.25 eV for conductivity. We have made boron carbide by PECVD from pentaborane and methane that is sufficiently isotropic to obtain resistivities as large as 1010 Ω cm at room temperature. This material is also shown to be suitable for photoactive p-n heterojunction diode fabrication in combination with Si(111).

Electronic properties of Sr14Cu24O41.

Crystals of orthorhombic ${\mathrm{Sr}}_{14}$${\mathrm{Cu}}_{24}$${\mathrm{O}}_{41}$ are semiconducting, with an activation energy of 0.18(2) eV for conduction along c, the direction lying parallel to both the (${\mathrm{Cu}}_{2}$${\mathrm{O}}_{3}$) planes and the (${\mathrm{CuO}}_{2}$) chains. The magnetic susceptibility above 80 K follows a Curie-Weiss law with \ensuremath{\theta}=-95 K and ${p}_{\mathrm{eff}}$=0.65${\ensuremath{\mu}}_{B}$/Cu in the ac plane and \ensuremath{\theta}=-190 and ${p}_{\mathrm{eff}}$=0.94${\ensuremath{\mu}}_{B}$/Cu along b, the direction perpendicular to the (${\mathrm{Cu}}_{2}$${\mathrm{O}}_{3}$) planes and the (${\mathrm{CuO}}_{2}$) chains. There is an indication of antiferromagnetic order below ${T}_{N}$=60 K, and a Curie contribution at low temperature due to localized free spins [0.4(1) with S=(1/2 per formula]. The specific heat measured in the range 2--12 K is of the form ${\mathrm{AT}}^{\mathrm{\ensuremath{-}}2}$+\ensuremath{\gamma}T+\ensuremath{\beta}${T}^{3}$, where A=1080 mJ K/mole, \ensuremath{\gamma}=100 mJ/mole ${\mathrm{K}}^{2}$, and \ensuremath{\beta}=5.93 mJ/mole ${\mathrm{K}}^{3}$. A 5-T magnetic field greatly enhances the low-temperature specific heat, an effect which is attributed to the localized states with S=(1/2. The linear term is attributed to a localized density of states with no net spin, possibly associated with peroxide ions. The relevance of these results to the low-temperature specific heat of copper-oxide superconductors is discussed.

Photoconductivity in single crystal polydiacetylene-toluene sulphonate

The photoconduction spectrum of the bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1,6-diol (PDA-TS) is reported in the photon energy range 0.62-3.1 eV for conduction along the polymer chain direction. A dominant feature of the spectrum is a steep photoconductive edge at 0.8 eV. This is an agreement with the existence of a localised impurity or defect electron energy level 0.8 eV below the conduction band, if electrons are the majority carriers. Electric field dependence of the photocurrent, examined in the range approximately 15-104 V cm-1, is interpreted on a model which indicates that for current flow parallel and perpendicular to the carbon backbone of the polymer chain, these crystals are model systems for the one- and three-dimensional versions of Onsager's theory (1934) of geminate recombination of bound electron-hole pairs respectively. Also reported are the results of optical transmission measurements on PDA-TS in the photon energy range 0.62-1.84 eV.

The Electrical Properties of Chromium Tribromide

AbstractThe electrical properties of vapor grown crystals of the hexagonal layer lattice material CrBr3 have been measured. From the temperature dependence of the Seebeck voltage and the resistivity it is concluded that the transport of the majority carriers, electrons, occurs by a hopping process. The activation energy for electron mobility is 0.56 eV for conduction along the c‐axis and 0.39 eV for conduction in the (0001) plane. The values of the effective drift mobilities in these two directions are 10−10 cm2/Vs and 10−7 cm2/Vs, respectively. Comparison of optical and photoconductivity data indicated that photoconductivity is associated with the crystal field optical transitions as well as the charge transfer bands.