Local fluctuations of absorber properties of Cu(In,Ga)Se2 by sub-micron resolved PL towards “real life” conditions

We analyze Cu(In,Ga)Se₂ absorber layers for solar cells in a confocal microscope setup by photoluminescence (PL) experiments. We present results on lateral inhomogeneities of absorbers in terms of local fluctuations of the splitting of quasi-Fermi levels (E_Fn − E_Fp), which determines the local open circuit voltage (V_oc) of the polycrystalline cell. These results can be extracted from spectrally resolved PL scans across several tens of microns. Excitation fluxes amount to 10² − 5 × 10⁴ suns equivalent at 83-300 K. We analyze the statistical distribution of the occurring fluctuations of (E_Fn − E_Fp) which we plot in histograms, seemingly showing Gaussian-like shapes. The width of these — showing substantial dependence on excitation flux and temperature — has been extrapolated towards 1 sun equivalent light fluxes. Furthermore, we use these results to correct the absolute values (E_Fn − E_Fp) which can be derived from non-laterally resolved, calibrated PL-studies at 300 K and 1 sun equivalent on comparatively large areas (1 mm²). The latter ones provide access to the spatially averaged PL-yields (∑Y_PL,xi) and their respective quasi-Fermi level splitting ((E_Fn − E_Fp)~ ln(∑Y_PL,xi)), while the average of the (E_Fn − E_Fp) from laterally resolved measurements reads (∑ln(Y_PL,xi)). We show a comparison of the two magnitudes and thus strongly appeal for sufficient high spatial resolution for a consistent quantitative interpretation of luminescence experiments.     

Effects of tunnel oxide process on SONOS flash memory characteristics

In this paper, various process conditions of tunnel oxides are applied in SONOS flash memory to investigate their effects on charge transport during the program/erase operations. We focus the key point of analysis on Fermi-level (E_F) variation at the interface of silicon substrate and tunnel oxide. The Si-O chemical bonding information which describes the interface oxidation states at the Si/SiO₂ is obtained by the core-level X-ray photoelectron spectroscopy (XPS). Moreover, relative E_F position is determined by measuring the Si 2p energy shift from XPS spectrums. Experimental results from memory characteristic measurement show that MTO tunnel oxide structure exhibits faster erase speed, and larger memory window during P/E cycle compared to FTO and RTO tunnel oxide structures. Finally, we examine long-term charge retention characteristic and find that the memory windows of all the capacitors remain wider than 2 V after 10⁵ s.     

XPS study of CZTSSe monograin powders

The surface and bulk composition of Cu₂ZnSn(Se_xS_1-x)₄ (CZTSSe) monograin powders were investigated by X-ray photoelectron spectroscopy (XPS). The concentration depth profiling of CZTSSe monograin powders was obtained by Ar⁺ ion etching.According to the XPS spectra of CZTSSe monograin powder, the binding energies of Zn 2p_3/2, Cu 2p_3/2, Sn 3d_5/2, S 2p_3/2 and Se 3d_5/2 core levels after surface cleaning are located at 1021.6 eV, 932.4 eV, 486.1 eV, 161.5 eV, 53.9 eV, respectively. From XPS depth profile analysis, Cu deficiency and the excess of chalcogenides on the powder crystals surface were observed.     

Growth of metal-oxide semiconductor nanocomposite thin films by a dual-laser, dual target deposition system

Nanocomposite formed by gold nanoparticles embedded in a titanium dioxide matrix thin films have been synthesized by a synchronized two laser system. An ArF? excimer (λ = 193 nm, τ_FWHM ∼ 12 ns) laser and a frequency tripled Nd:Yttrium Aluminium Garnet (YAG; λ = 355 nm, τ_FWHM ∼ 10 ns) laser were used for the irradiation of titanium dioxide and gold targets. The investigations showed that there exists the possibility for tailoring the optical properties of gold-titanium dioxide nanocomposites by the proper choice of the laser irradiation parameters. The band gap narrowing and additional absorption in the visible spectral region induced by the incorporation of gold in the host TiO₂ matrix allows for the design of nanostructured thin films for new generation of photocatalysts or solar energy converters.     

Structure, conductivity, and optical absorption of Ag2−xO films

Evaporation of Ag in the presence of an electron cyclotron resonance (ECR) oxygen plasma was used to deposit Ag_2−xO films with a range of stoichiometries onto r-plane sapphire substrates. A quartz crystal oscillator (QCO) was used to accurately measure the silver and oxygen arrival rates and establish the O/Ag flux ratio needed to produce films with nominal Ag₂O stoichiometry. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis indicates that the Ag_2−xO films are not single phase but contain signatures of coexisting Ag₂O and AgO components. XRD shows that the lattice matching with the r-plane sapphire substrate causes the Ag₂O phase to grow with <002> heteroepitaxial crystallites coexisting with crystallites having <111> normal and random in-plane orientation. The AgO phase also forms with crystallites having <002> heteroepitaxy as well as crystallites with <111> normal and random in-plane orientation. The mixed phase Ag_2−xO films exhibit approximately 77% optical transmission over the visible range (500 nm to 700 nm) and have a single absorption edge near 3.3 eV. Four-point van der Pauw conductivity and Hall effect measurements indicate that the Ag_2−xO films are p-type with a conductivity on the order of 3 × 10^− 3 Ω^− 1 cm^− 1.     

Thin film preparation and characterization of wide band gap Cu3TaQ4 (Q = S or Se) p-type semiconductors

The structural, optical, and electronic properties of thin films of a family of wide band gap (E_g > 2.3 eV) p-type semiconductors Cu₃TaQ₄ (Q = S or Se) are presented. Thin films prepared by pulsed laser deposition of ceramic Cu₃TaQ₄ targets and ex-situ annealing of the as-deposited films in chalcogenide vapor exhibit mixed polycrystalline/[100]-directed growth on amorphous SiO₂ substrates and strong (100) preferential orientation on single-crystal yttria-stabilized zirconia substrates. Cu₃TaS₄ (E_g = 2.70 eV) thin films are transparent over the entire visible spectrum while Cu₃TaSe₄ (E_g = 2.35 eV) thin films show some absorption in the blue. Thin film solid solutions of Cu₃TaSe_4 − xS_x and Cu₃TaSe_4 − xTe_x can be prepared by annealing Cu₃TaSe₄ films in a mixed chalcogenide vapor. Powders and thin films of Cu₃TaS₄ exhibit visible photoluminescence when illuminated by UV light.     

Study of the growth of CuAlS2 thin films on oriented silicon (111)

Within the chalcopyrite family the sulphur based compounds CuMS₂ (M = In, Ga, Al) have attracted much interest in recent years because they show a direct wide band-gap covering from E_gap = 1.53 eV (CuInS₂) over E_gap = 2.43 eV (CuGaS₂) to E_gap = 3.49 eV (CuAlS₂). Therefore they are particularly suitable for optoelectronic as well as photovoltaic applications. The CuAlS₂ semiconductor is one of these compounds and has good luminescent properties and a wide direct gap of 3.5 eV making it suitable for the use as material for light-emitting devices in the blue region of the spectrum. To dig up fully its potential a better understanding of the fundamental properties of the CuAlS₂ film itself is essential, which could be achieved from high-quality single-crystalline materials. So, the aim of this work has been to study the growth of multilayer CuAlS₂ thin films on Si(111) substrates at a substrate temperature of 723 K. One, two and three layers with 60, 120 and 180 nm thicknesses, respectively, were deposited on Si(111) substrate. The effect of the CuAlS₂ layer numbers on the structure, morphology and optical properties of the samples was investigated. The X-ray diffraction studies revealed that all the samples are polycrystalline in nature, single CuAlS₂ phase and exhibiting chalcopyrite structure with a preferred orientation along the (112) direction. However, the sample with three CuAlS₂ layers exhibit the highly oriented (112) plane with grain sizes of 80 nm. So we show that this experimental process affects significantly the structural properties of the CuAlS₂ films. Raman spectroscopic measurements indicated five prominent peaks at 193, 205, 325, 335 and 370 cm^− 1. The possible origin of the 370 cm^− 1 peak was investigated and was found to be some local vibration in the structure. The peaks at 193-205 and 335 cm^− 1 were ascribed to A₁ and B₂ modes, respectively.     

Structural and mechanical properties of titanium and titanium diboride monolayers and Ti/TiB2 multilayers

Nano-multilayers represent a new class of engineering materials that are made up of alternating nanometer scale layers of two different components. In the present work a titanium (Ti) monolayer was combined with titanium diboride (TiB₂) to form a Ti/TiB₂ nano-multilayer. Designed experimental parameters enabled an evaluation of the effects of direct current bias voltage (U_b) and bilayer thickness (Λ) during multilayer deposition on the mechanical properties of reactively sputtered Ti/TiB₂ multilayer films. Their nanostructures and mechanical properties were characterized and analyzed using X-ray photoelectron spectroscopy (XPS), low-angle and high-angle X-ray diffraction (XRD), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), and microindentation measurements. Under the optimal bias voltage of U_b = − 60 V, it was found that Λ (varied from 1.1 to 9.8 nm) was the most important factor which dominated the nanostructure and hardness. The hardness values obtained varied from 12 GPa for Ti and 15 GPa for TiB₂ monolayers, up to 33 GPa for the hardest Ti/TiB₂ multilayer at Λ = 1.9 nm. The observed hardness enhancement correlated to the layer thickness, followed a relation similar to the Hall-Petch strengthening dependence, with a generalized power of ∼ 0.6. In addition, the structural barriers between two materials (hcp Ti/amorphous TiB₂) and stress relaxation at interfaces within multilayer films resulted in a reduction of crack propagation and high-hardness.     

Interpretation of quasi-Fermi level splitting in Cu(Ga,In)Se2-absorbers by confocally recorded spectral luminescence and numerical modeling

Spectral room temperature photoluminescence (pl) of polycrystalline Cu(In,Ga)Se₂ films (CIGSe) is evaluated with respect to optoelectronic properties and in particular for the determination of the splitting of quasi-Fermi levels (E_Fn − E_Fp). For lateral resolution of ≤ 1 µm a confocal pl-setup is used. The depth profile of the excess carrier densities determining the rates of radiative transitions strongly govern the spectral pl-shape which has been numerically modeled with a matrix transfer formalism. In this optical approach we discriminate for wave propagation and attenuation in a multilayer system between a plane-wave ansatz and a 3D-spherical formalism, depending on excitation area large or small/similar compared to the thickness of the absorber. In both cases re-absorption of photons in energetic regimes with absorption approaches unity, from which the splitting of the quasi-Fermi levels is preferentially deduced, substantially influence the spectral luminescence signal. For heterojunctions usually located at the light entrance side of the device our evaluation with good agreement reflects (E_Fn − E_Fp) in the vicinity of the barrier and thus indicates the maximum achievable open circuit voltage of the finally processed diode. Departures of the spectral pl from the idealized Bose-term signalize unfavorable carrier profiles and a depth dependence of optoelectronic absorber properties.     

Interfacial characteristics and dielectric properties of Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) depth profiling data show that each element component of the BST film possesses a uniform distribution from the outermost surface to subsurface, but obvious Ti-rich is present to BST/Pt interface because Ti⁴⁺ cations are partially reduced to form amorphous oxides such as TiO_x (x < 2). Based on the measurement of XPS valence band spectrum, an energy band diagram in the vicinity of BST/Pt interface is proposed. Dielectric property measurements at 1 MHz reveal that dielectric constant and loss tangent are 323 and 0.0095 with no bias, while 260 and 0.0284 with direct current bias of 25 V; furthermore, tunability and figure of merit are calculated to be 19.51% and 20.54, respectively. The leakage current density through the BST film is about 8.96 × 10^− 7 A/cm² at 1.23 V and lower than 5.66 × 10^− 6 A/cm² at 2.05 V as well as breakdown strength is above 3.01 × 10⁵ V/cm.     

CuInSe2 monograin growth in the liquid phase of potassium iodide

The results of monograin CuInSe₂ synthesis from Cu-In alloy and Se in liquid KI are presented. The amounts of CuInSe₂ and KI were nearly equal to fulfil the criterion for the monograin growth (all free volume between the particles has to be filled with liquid). All the grown powder materials with narrow-disperse granularity were chalcopyrite CuInSe₂. The grown crystallites had tetrahedral shapes and homogeneous composition. Particle size distribution was used to describe the growth process. The activation energy of linear growth of crystals was E_d = 0.25 ± 0.05 eV, and the power of time dependence of the crystal growth was l/n = 0.26 ± 0.06. The solubility of CuInSe₂ in KI at 990 K was 0.17 ± 0.05 wt. %. The solubility of potassium and iodine in CuInSe₂ at 990 K was 0.094 wt. %, and 0.0086 wt. %, respectively. As a result, homogeneous p-type CuInSe₂ monograin materials were synthesised in KI solvent.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

ZnO and Zn1−xCdxO nanocrystallites obtained by oxidation of precursor Langmuir-Blodgett multilayers

ZnO and Zn_1−xCd_xO nanocrystallites were prepared by oxidation of zinc arachidate-arachidic acid and zinc arachidate-cadmium arachidate-arachidic acid LB multilayers, respectively. The metal content of the multilayers was controlled by manipulation of subphase composition and pH. Precursor multilayers were oxidized in the temperature range of 400 °C-700 °C. The formation of ZnO and Zn_1−xCd_xO was confirmed by UV-Visible spectroscopy. Uniformly distributed, isolated and nearly mono-dispersed nanocrystallites of ZnO (11 ± 3 nm) and Zn_1−xCd_xO (18 ± 6 nm) were obtained.     

Electronic parameters and top surface chemical stability of RbPb2Br5

The RbPb₂Br₅ crystal has been grown by Bridgman method. The electronic structure of RbPb₂Br₅ has been measured with XPS for a powder sample. High chemical stability of RbPb₂Br₅ surface is verified by weak intensity of O 1s core level recorded by XPS and structural RHEED measurements. Chemical bonding effects have been observed by the comparative analysis of element core levels and crystal structure of RbPb₂Br₅ and several rubidium- and lead-containing bromides using binding energy difference parameters Δ_Rb = (BE Rb 3d − BE Br 3d) and Δ_Pb = (BE Pb 4f_7/2 − BE Br 3d).     

The study on electrical behavior of Gd2O3-WO3 complex ceramics at high temperature

Gd₂O₃-WO₃ complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd₂W₂O₉ is the main phase and Gd₂O₃ is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd₂O₃-WO₃ complex ceramics can be simply explained.     

The microwave-assisted synthesis and characterization of Zn1 − xCoxO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn_1 − xCo_xO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn_1 − xCo_xO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn_1 − xCo_xO nanoparticles. The XRD study shows that for Co doping up to 5%, Co²⁺ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn_1 − xCo_xO (x = 1-5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co²⁺ ions in the tetrahedral sites. The Raman study shows that the linewidth of E₂^low mode increases with Co concentration, which further indicates the incorporation of Co²⁺ ions into the ZnO host matrix.     

Estimation of oxidation states of AlOx barriers in a tunneling junction by inelastic electron tunneling spectroscopy

Co/AlO_x/Co with AlO_x barriers of various oxidation states were fabricated and investigated using inelastic electron tunneling (IET) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS revealed that AlO_x oxidized for 8 h contained an inhomogeneous distribution of metallic Al, whereas AlO_x oxidized for 24 h contained a homogeneous distribution. The inhomogeneous and homogeneous distributions of metallic Al corresponded to asymmetric and symmetric IET spectra, respectively. These junctions showed peaks at ± 0.03 V. AlO_x oxidized for 168 h contained no metallic Al, and this junction had no peaks, suggesting that peaks at ± 0.03 V originate from metallic Al.     

Synthesis of LiNi0.9Co0.1O2 cathode material for lithium secondary battery by a novel route

The cathode material, LiNi_0.9Co_0.1O₂ was prepared using a rheological phase reaction method with LiOH·H₂O, home-made Ni(OH)₂, and Co₂O₃ as starting materials. At first, the mixture of reactants and a proper amount of water reacted to form a rheological precursor. Then the dried precursor was heated at 730 °C in one step to yield the product. The effects of calcination time (between 0.5 and 10 h) on the structural, morphological and electrochemical properties were investigated. All obtained powders show a single phase with α-NaFeO₂ structure (R-3m space group). The sample prepared in 2.5 h delivers the largest initial discharge capacity of 218 mA h g^− 1 (3.0-4.35 V, 25 mA g^− 1) and still remains 192 mA h g^− 1 after 15 cycles. The method is simple, economical and effective and is promising for practical application.     

Preparation and luminescence properties of nanocrystalline La2O3:Eu phosphor

Powders La₂O₃ doped with 1 mol% Eu were prepared via a combustion route using different reducers (urea, glycine and citric acid). The structure and morphology were determined with XRD and HRTEM measurement. The main emission positions centered at 626 nm for ⁵D₀ → ⁷F₂ transition are observed. The variation of CT band with different reducers is observed. The intensity of ⁵D₀ → ⁷F₂ transition centered at 626 nm with respect to that of ⁵D₀ → ⁷F₁ transition is a function of the energy difference ΔE between the two CT band positions.     

Compositional, structural and electronic characteristics of HfO2 and HfSiO dielectrics prepared by radio frequency magnetron sputtering

HfO₂ and HfSiO films were prepared on Si substrates by using radio frequency magnetron sputtering (RFMS). Compositional, structural and electronic properties of the two films were investigated completely. X-ray photoelectron spectroscopy (XPS) spectra showed that the atom ratio of Hf to O was about 1:2 in the HfO₂ film and the chemical composition of the HfSiO film was Hf₃₇Si₇O₅₆. Grazing incidence X-ray diffraction (GI-XRD) patterns indicated crystallization in the HfO₂ film after 400 °C annealing, but there is no detectable crystallization in the HfSiO film after 800 °C annealing. C-V measurements indicated that the dielectric constants for the HfO₂ and HfSiO film were 20.3 and 17.3, respectively. The fixed charge densities were found to be 6.0 × 10¹² cm⁻² for the HfO₂ film and 3.7 × 10¹² cm⁻² for the HfSiO film. I-V characteristics showed that the average leakage current densities were 2.4 μA/cm² for the HfO₂ film and 0.2 μA/cm² for the HfSiO film at the gate bias of 1 V.