Study of the light-induced degradation of tandem α-Si:H/μc-Si:H photovoltaic converters

The photo-induced degradation of tandem α-Si:H/μc-Si:H photovoltaic converters with an initial efficiency of 10.4% under light flux densities of 1 and 10 kW m^?2 (AM1.5G) is studied. It is shown that the stabilized state is reached after 500 h of exposure to the standard light-flux density and after 300 min at a flux 10 times higher in density. In both cases, the efficiency decreases by 1.2–1.4 abs. %. The experimentally measured spectral and current-voltage characteristics of the photovoltaic converters are used to determine the nonequilibrium carrier lifetimes and to calculate variation dependences of the dangling-bond concentration in i-α-Si:H and i-μc-Si:H layers. The dependences are approximated in terms of the floating-bond model. The calculated dangling-bond concentrations after various exposure times are used to simulate the dependences of the photovoltaic-converter parameters on light exposure. The results obtained show good coincidence between the simulated degradation rates of the current and efficiency of a tandem photovoltaic cell and the experimental data.     

Method for studying the light-induced degradation of α-Si:H/μc-Si:H tandem photovoltaic converters under increased illuminance

An experimental installation and the procedure for its use in accelerated tests of thin-film α-Si:H/μc-Si:H photovoltaic converters with dimensions of up to 100 × 100 mm on light-induced degradation under an increased illumination level (up to 10 kW/m²) are described. Estimates of the levels of photoinduced degradation of photovoltaic converters, obtained by conventional and developed procedures, are compared and it is demonstrated that the procedure for studying the photoinduced degradation at an increased illumination level can make the test duration 100 times shorter while providing fully adequate assessment of the stability of photovoltaic converters based on amorphous and microcrystalline silicon.     

A primal-dual gradient method for image decomposition based on (<Emphasis Type=Italic>BV</Emphasis>, <Emphasis Type=Italic>H</Emphasis><Superscript>−1</Superscript>)

The main aim of this paper is to accelerate the image decomposition model based on (BV, H ⁻¹). It is solved with a particularly effective primal-dual gradient descent algorithm. The algorithm works on the primal-dual formulation and exploits the information of the primal and dual variables simultaneously. It converges significantly faster than some popular existing methods in numerical experiments. This approach is to some extent related to projection type methods for solving variational inequalities.     

Degradation of micromorphous thin-film silicon (α-Si/μ<Emphasis Type="Italic">c</Emphasis>-Si) solar modules: Evaluation of seasonal efficiency based on the data of monitoring

A method for assessing the efficiency of α-Si/μc-Si solar modules is developed; the method is based on monitoring current and voltage at the point of highest voltage and on measuring the temperature at the surface of the module. The technique for assessment of the parameters of the α-Si/μc-Si modules in the course of their operation after initial degradation of the module is described; the results of parameter evaluation are compared with the values measured in the laboratory. The error in evaluating parameters was no larger than 3%; this error amounted to 0.36% in the case of estimating the parameters under standard conditions and maximal power of the module. This method can be used for evaluating a module’s efficiency and for short-term prediction (day, week) of the power generated by a solar power plant under conditions of operation using standard tools for monitoring.     

Effect of Hydrogen Free Radicals on Hg<Subscript>1−<Emphasis Type=Italic>x</Emphasis></Subscript>Cd<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>Te

The effects of atomic hydrogen (H) and Br/methanol etching on Hg_1−x Cd _x Te films were investigated using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Exposure of an as-received Hg_1−x Cd _x Te sample to H + H₂ resulted in H-induced TeO₂ reduction. The oxide reduction was first order with respect to H + H₂ exposure. Exposure to H + H₂ after etching the Hg_1−x Cd _x Te film in a Br/methanol solution induced Hg and C depletion. Hg and C removal was also observed after completely reducing the TeO₂ on the as-received sample. The removal process was hindered by the formation of a Cd-rich overlayer on both etched and unetched surfaces.     

On the analysis of parameter <Emphasis Type=Italic>γ</Emphasis> in fast TCP

The limits of parameter γ in FAST TCP are studied in this paper. A continuous time fluid flow model of the link buffer is considered to create a linear control system related to FAST TCP. Linearing the fluid flow model and window control model, the Laplace transform version of congestion control system are presented. It results in a negative feedback system with open loop transfer function. With the analysis of Nyquist curve of the system, a sufficient condition on asymptotical stability of FAST TCP congestion window related to the parameter γ is obtained. Packet level ns-2 simulations are used to verify the theoretical claims.     

Effect of γ-ray radiation on electrical properties of heat-treated Tb<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type=Italic>x</Emphasis></Subscript>Se single crystals

The effect of γ-ray radiation on the electrical properties of heat-treated Tb_0.01Sn_0.99Se (sample 1) and Tb_0.05Sn_0.95Se (sample 2) samples is studied. It is found that, as a result of irradiation with γ-ray 1.25-MeV photons, the charge-carrier concentration decreases in the temperature range T = 77−200 K by 17 and 6.3% for samples 1 and 2, respectively. It is assumed that, in the course of irradiation with γ-ray photons, terbium impurity atoms are located between sites of the crystal lattice; in addition, Frenkel defects are formed.     

Electric properties of (SiC)<Subscript>1 − <Emphasis Type=Italic>x</Emphasis></Subscript>(AlN)<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>/SiC anisotropic heterostructures

The heterostructures of p-(SiC)_{1 − x} (AlN) _x / _n -6H-SiC are synthesized by means of sublimation epitaxy of (SiC)_{1 − x} (AlN) semiconductor solid solutions at 6H-SiC substrates. The results of the investigation of the concentration and temperature dependences on current-voltage characteristics (CVCs) are presented. It is revealed that due to the high potential barriers the forward current is caused by the tunneling and recombination processes of charge carriers via states at the boundary surface.     

Crystal Structure and High-Temperature Thermoelectric Properties of the Mo<Subscript>3−<Emphasis Type=Italic>x</Emphasis></Subscript>Ru<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>Sb<Subscript>7</Subscript> Compounds

Zintl phases are currently receiving great attention for their thermoelectric potential typified by the discovery of a high ZT value in Yb₁₄MnSb₁₁-based compounds. Herein, we report on the crystallographic characterization via neutron and x-ray diffraction experiments, and on the thermoelectric properties measured in the 300 K to 1000 K temperature range, of Mo₃Sb₇ and its isostructural compounds Mo_3−x Ru _x Sb₇. Even though Mo₃Sb₇ displays rather high ZT values given its metallic character, the partial substitution of Mo by Ru substantially improves its thermoelectric properties, resulting in a ZT value of ∼0.45 at 1000 K for x = 0.8.     

Study of dielectric processes in (As<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>1 − <Emphasis Type=Italic>x</Emphasis></Subscript>Bi<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript> amorphous films

A comparative analysis of dielectric polarization processes in undoped and Bi-doped layers of modified As₂Se₃ has been performed. It is established that both the similarity and difference in polarization phenomena are due to specific features of the internal structure of studied materials. The mechanism of the observed effects is discussed.     

Influence of the defect structure of γ-La<Subscript>2(1 − <Emphasis Type=Italic>x</Emphasis>)</Subscript>Nd<Subscript>2<Emphasis Type=Italic>x</Emphasis></Subscript>S<Subscript>3</Subscript> crystals on their spectroscopic properties

The photoluminescence and Raman scattering of undoped γ-Ln₂S₃ single crystals (Ln is a rare earth ion) and the decay kinetics of the ⁴ F _3/2 level of Nd ions in these crystals have been investigated. The distortion of the decay curve of the Nd ⁴ F _3/2 level upon excitation by light with λ = 0.53 μm is explained.     

Coherent phase equilibria in the Zn-Cd-Te system and liquid-phase epitaxy of elastically strained Zn<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>Cd<Subscript>1 − <Emphasis Type=Italic>x</Emphasis></Subscript>Te alloy layers

The effect of elastic strains produced in epitaxial Zn _x Cd_{1 − x} Te alloy layers during deposition on the CdTe substrate on the parameters of growth is studied experimentally and theoretically. Phase equilibria between the elastically strained alloy layer, the crystal lattice of which is continuously (coherently) matched to the crystal lattice of the bulk substrate, are described by a coherent state diagram. The processes of mass transfer during the formation of heterostructures on the basis of the above-mentioned alloys and the substrate formed of the initial binary compounds are described in the context of the model of diffusion-limited crystallization. It is shown that such thermodynamic concepts can be used to describe experimental data on the parameters of the process of crystallization of elastically strained alloy layers during the formation of heterojunctions in the system involving the Zn-Cd-Te alloy and the substrate based on the initial binary compound.     

Synthesis of Ge<Subscript>1−<Emphasis Type=Italic>x</Emphasis></Subscript>Sn<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript> Alloy Thin Films Using Ion Implantation and Pulsed Laser Melting (II-PLM)

Ge_1−x Sn _x thin films are interesting for all-group-IV optoelectronics because of a crossover to a direct bandgap with dilute Sn alloying. However, Sn has vanishing room-temperature equilibrium solubility in Ge, making their synthesis very challenging. Herein, we report on our attempts to synthesize Ge_1−x Sn _x films on Ge (001) using ion implantation and pulsed laser melting (II-PLM). A maximum of 2 at.% Sn was incorporated with our experimental conditions in the samples as determined by Rutherford back scattering spectroscopy. A red-shift in the Ge optical phonon branch and increased absorption below the Ge bandgap with increasing Sn concentration indicate Sn-induced lattice- and band-structure changes after II-PLM. However, ion-channeling and electron microscopy show that the films are not of sufficient epitaxial quality for use in devices.