Interfacial lithium-ion transfer at the LiMn2O4 thin film electrode/aqueous solution interface

Interfacial lithium-ion transfer at the LiMn₂O₄ thin film electrode/aqueous solution was investigated. The cyclic voltammograms of the film electrode conducted in the aqueous solution was similar to an adsorption-type voltammogram of reversible system, suggesting that fast charge transfer reaction proceed in the aqueous solution system. We found that the activation energy for this interfacial lithium-ion transfer reaction obtains 23–25 kJ mol⁻¹, which is much smaller than that in the propylene carbonate solution (50 kJ mol⁻¹). This small activation energy will be responsible for the fast interfacial lithium-ion transfer reaction in the aqueous solution. These results suggest that fast lithium insertion/extraction reaction can be realized by decreasing the activation energy for interfacial lithium-ion transfer reaction.     

Pyrite (FeS2) thin films prepared by spray method using FeSO4 and (NH4)2Sx

A simple spray method for the preparation of pyrite (FeS₂) thin films has been studied using FeSO₄ and (NH₄)₂S_x as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H₂S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 10¹⁶–10²⁰ cm⁻³ and a Hall mobility (μ_H) in the range 200–1 cm²/V s. The best electrical properties (p=7×10¹⁶ cm⁻³, μ_H=210 cm²/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO₄ solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films.     

Cu(In,Ga)Se2 solar cells on stainless steel substrates covered with insulating layers

We have developed the flexible Cu(In,Ga)Se₂ (CIGS) solar cells on the stainless steel substrates with the insulating layer for the fabrication of the integrated module. The CIGS films have strong adhesion to the Mo films with insulating layers. An efficiency of 12.3% was achieved by the flexible CIGS solar cell with a structure of ITO/ZnO/CdS/CIGS/Mo/SiO₂/stainless steel. The insertion of the SiO₂ insulating layer did not have an influence on the formation of the CIGS film and solar cell performances.     

Preparation and electrochemical properties of strontium doped Pr2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Pr_2−xSr_xNiO₄ (PSNO, x = 0.3, 0.5 and 0.8) cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC) were synthesized by a glycine-nitrate process using Pr₆O₁₁, Ni(NO₃)₂·6H₂O and SrCO₃ powders as raw materials. Phase structure of the synthesized powders was characterized by X-ray diffraction analysis (XRD). Microstructure of the sintered PSNO samples was observed and thermal expansion coefficient (TEC) and electrical conductivity were investigated. Electrochemical impedance spectroscopy (EIS) measurement of the PSNO materials on Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte was carried out, and single cells based on the PSNO cathodes were also assembled and their performances were tested. The results show that the synthesized PSNO powders have pure K₂NiF₄-type structure and the PSNO materials are chemically stable with Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte. The sintered PSNO samples have porous and fine microstructure with pore size smaller than 1 μm. Average thermal expansion coefficient of the PSNO materials is about 12–13 × 10⁻⁶ K⁻¹ at 200–800 °C and the electrical conductivity is in the range of 70–120 Scm⁻¹ at 800 °C. Area specific resistance (ASR) of the Pr_2−xSr_xNiO₄ materials on SCO electrolyte is 0.407 Ωcm², 0.126 Ωcm² and 0.112 Ωcm² for x = 0.3, 0.5 and 0.8 at 800 °C, respectively. Maximum open circuit voltage (OCV) and power density of the single NiO-SCO/SCO/PSNO cells are 0.75 V and 298 mWcm⁻² at 700 °C, respectively, which indicates that Pr_2−xSr_xNiO₄ may be a potential cathode material for IT-SOFC.     

Improved Cu(In,Ga)(S,Se)2 thin film solar cells by surface sulfurization

Surface sulfurization was developed as a technique for fabricating efficient ZnO : Al/CdS/graded Cu(In,Ga)(S,Se)₂/ Mo/glass solar cells. Prior to the sulfurization, single-graded Cu(In,Ga)Se₂ (CIGS) films were deposited by a multi-stage process. The sulfurization of CIGS films was carried out using a H₂S---Ar mixture at elevated temperatures. The crystallographic and compositional properties of the absorber layers were investigated by XRD, SEM and AES analyses. After sulfurization, sulfur atoms were substituted for selenium atoms at the surface layer of CIGS films to form a Cu(In,Ga)(S,Se)₂ absorber layer. The diffusion of sulfur depends strongly on the grain structure of CIGS film. The cell efficiency of the 8–11% range before sulfurization was improved dramatically to 14.3% with V_oc = 528 mV, J_sc = 39.9 mA/cm² and FF = 0.68 after the sulfurization process.     

HDMR correlations for the laminar burning velocity of premixed CH4/H2/O2/N2 mixtures

Correlations for the laminar burning velocity of premixed CH₄/H₂/O₂/N₂ mixtures were developed using the method of High Dimensional Model Representation (HDMR). Based on experiment data over a wide range of conditions reported in the literature, two types of HDMR correlation (i.e. global and piecewise HDMR correlations) were obtained. The performance of these correlations was assessed through comparison with experimental results and the correlation reported in the literature. The laminar burning velocity predicted by the piecewise HDMR correlations was shown to agree very well with those from experiments. Therefore, the piecewise HDMR correlations can be used as an effective replacement for the full chemical mechanism when the prediction of the laminar burning velocity is needed in certain combustion modeling.     

The effect of NaF on Cu(In, Ga)Se2 thin film solar cells

This work investigates NaF, on Mo coated sodium barrier glass, as a sodium precursor for the growth of Cu(In, Ga)Se₂ for thin film solar cells. These precursor layers are investigated by X-ray photoelectron spectroscopy (XPS) before and after annealing, and after exposure to selenium. XPS is also performed on the Cu(In, Ga)Se₂ layer, deposited with NaF. The influence of the NaF on the absorber growth is studied by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The electrical properties are investigated by cell fabrication and characterization. Cell results are comparable when NaF or out-diffusion of sodium from the soda lime glass are used.     

Cu(In,Ga)Se2 thin-film solar cells with an efficiency of 18%

An efficiency of over 18% have been achieved in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells. Solar cell parameters were estimated for the cells with efficiencies of more and less than 18%. A diode quality factor n and forward current (saturated current) J₀ of the cell with over 18% efficiency are lower than those with below 18% efficiency. This would be attributed to sufficient coverage of the CdS film with excellent uniformity as a buffer and/or window layer over the CIGS film because the process of CdS film formation was improved.     

Nanostructure Cu2ZnSnS4 thin film prepared by sol–gel for optoelectronic applications

Thin film of Cu₂ZnSnS₄ (CZTS) has been successfully deposited by sol–gel technique on n-type silicon and glass substrates to fabricate a heterojunction photodiode. The structural properties of the film were investigated by atomic force microscopy. The AFM image of the Cu₂ZnSnS₄ film reveals that the film is a nanostructure material formed from nanoparticles with the particle size of 50–90 nm. The optical band gap, E_g of the Cu₂ZnSnS₄ film was found to be 1.48 eV and the obtained optical band gap suggests that CZTS is very suitable for photovoltaic and optoelectronic applications. The current–voltage characteristics of the Al/n-Si/Cu₂ZnSnS₄/Al diode exhibit a good rectification behavior with ideality factor of 2.84 and barrier height of 0.738 eV. The interface states of the diode were analyzed by series resistance and conductance-voltage methods. The presence of interface states in series resistance–voltage plots was confirmed by the illumination. The interface state density D_it for the diode was found to be 3.63 × 10¹² eV⁻¹ cm⁻². The obtained results indicate that the Al/n-Si/Cu₂ZnSnS₄/Al diode is a photosensor based on controlling of interface states by illumination.     

Thermal decomposition of (NH4)2SO4 in presence of Mn3O4

The main objective of this work is to develop a hybrid water-splitting cycle that employs the photon component of sunlight for production of H₂ and its thermal (i.e. IR) component for generating oxygen. In this paper, (NH₄)₂SO₄ thermal decomposition in the presence of Mn₃O₄, as an oxygen evolving step, was systematically investigated using thermogravimetric/differential thermal analyses (TG/DTA), temperature programmed desorption (TPD) coupled with a mass spectrometer (MS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) techniques. Furthermore, thermolysis of ammonium sulfate, (NH₄)₂SO₄, in the presence of Mn₃O₄ was also investigated by conducting flow reactor experiments. The experimental results obtained indicate that at 200-450 °C, (NH₄)₂SO₄ decomposes forming NH₃ and H₂O and sulfur trioxide that in the presence of manganese oxide react to form manganese sulfate, MnSO₄. At still higher temperatures (800∼900 °C), MnSO₄ further decomposed forming SO₂ and O₂.     

Surface sulfurization studies of Cu(InGa)Se2 thin film

Sulfurization of copper indium gallium diselenide (CIGS) thin films solar cell absorber has been used to enhance the open-circuit voltage of the device by increasing the band gap of the absorber near the interface. Sulfurization of a homogeneous co-evaporated Cu(InGa)Se₂ thin film was studied in hydrogen sulfide and in a mixture of hydrogen sulfide and hydrogen selenide gases with the inclusion of oxygen. The structural and compositional properties of the absorber layer were investigated by XRD, EDS and AES. Sulfurization in hydrogen sulfide gas forms a fully converted sulfide layer at the top of the absorber layer, which in turn forms a barrier for the current collection. Sulfurization in a mixture of hydrogen sulfide and hydrogen selenide gases forms a wide band gap Cu(InGa)(SeS)₂ layer at the surface, but at the same time there is Ga diffusion away from the surface with the inclusion of sulfur at the surface.     

Photoconductivity of Cu(In, Ga) Se2 films

Polycrystalline CuIn_{1 − x}Ga_xSe₂ (0 ≤ x < 0.3) films (CIGS) were deposited by coevaporating the elements from appropriate sources onto glass substrates (substrate temperature 720 to 820 K). Photoconductivity of the polycrystalline CIGS films with partially depleted grains were studied in the temperature range 130–285 K at various illumination levels (0–100 mW/cm²). The data at low temperature (T < 170 K) were analyzed by the grain boundary trapping model with monovalent trapping states. The grain boundary barrier height in the dark and under illumination were obtained for different x-values of CuIn_1−xGa_xSe₂ films. Addition of Ga in the polycrystalline films resulted in a significant decrease in the barrier height. Variation of the barrier height with incident intensity indicated a complex recombination mechanism to be effective in the CIGS films.     

The structural characterization of (NH4)2B10H10 and thermal decomposition studies of (NH4)2B10H10 and (NH4)2B12H12

The structure of (NH₄)₂B₁₀H₁₀ (1) was determined through powder XRD analysis. The thermal decomposition of 1 and (NH₄)₂B₁₂H₁₂ (2) was examined between 20 and 1000 °C using STMBMS methods. Between 200 and 400 °C a mixture of NH₃ and H₂ evolves from both compounds; above 400 °C only H₂ evolves. The dihydrogen bonding interaction in 1 is much stronger than that in 2. The stronger dihydrogen bond in 1 resulted in a significant reduction by up to 60 °C, but with a corresponding 25% decrease in the yield of H₂ in the lower temperature region and a doubling of the yield of NH₃. The decomposition of 1 follows a lower temperature exothermic reaction pathway that yields substantially more NH₃ than the higher temperature endothermic pathway of 2. Heating of 1 at 250 °C resulted in partial conversion of B₁₀H₁₀²⁻ to B₁₂H₁₂²⁻. Both 1 and 2 form an insoluble polymeric material after decomposition. The elements of the reaction network that control the release of H₂ from the B₁₀H₁₀²⁻ can be altered by conducting the experiment under conditions in which pressures of NH₃ and H₂ are either near, or away from, their equilibrium values.     

Electrical properties of the Cu(In,Ga)Se2/ MoSe2/Mo structure

We investigated the electrical properties of the Cu(In,Ga)Se₂/MoSe₂/Mo structure. CIGS/Mo heterocontact including the MoSe₂ layer is not Schottky-type but a favorable ohmic-type contact by the evaluation of dark I–V measurement at low temperature. A characteristic peak at 870 nm is observed in differential quantum efficiency of a solar cell with a CIGS thickness of 0.5 μm. This peak is considered with relating to the absorption of the MoSe₂ layer. The band gap of MoSe₂ is calculated to be 1.41 eV from the absorption peak. The band diagram is discussed on the basis of the electrical point of view.     

Highly efficient Cu(In,Ga)Se2 mini-modules

In this contribution, we present results and the philosophy of our mini-module efforts. These efforts have achieved world record levels as well as a reproducible process. Various mini-module designs are tested using two different baseline Cu(In,Ga)Se₂ deposition recipes. Gridded mini-modules achieve highest efficiencies and are much less demanding on the ZnO:Al top contact than their conventional counterpart. For all of the designs tested, our experimental results are in the order of the expectations from our modeling. Gridded modules can achieve efficiency levels very close to those of the cells.     

Role of CO2 in the CH4 oxidation and H2 formation during fuel-rich combustion in O2/CO2 environments

The effect of CO₂ reactivity on CH₄ oxidation and H₂ formation in fuel-rich O₂/CO₂ combustion where the concentrations of reactants were high was studied by a CH₄ flat flame experiment, detailed chemical analysis, and a pulverized coal combustion experiment. In the CH₄ flat flame experiment, the residual CH₄ and formed H₂ in fuel-rich O₂/CO₂ combustion were significantly lower than those formed in air combustion, whereas the amount of CO formed in fuel-rich O₂/CO₂ combustion was noticeably higher than that in air. In addition to this experiment, calculations were performed using CHEMKIN-PRO. They generally agreed with the experimental results and showed that CO₂ reactivity, mainly expressed by the reaction CO₂ + H → CO + OH (R1), caused the differences between air and O₂/CO₂ combustion under fuel-rich condition. R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO₂ was to advance CH₄ oxidation during fuel-rich O₂/CO₂ combustion. Under fuel-rich combustion, H₂ was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H₂O production. In fact, these hydrocarbon reactions were competitive. With increasing H/OH ratio, H₂ formed more easily; however, CO₂ reactivity reduced the H/OH ratio by converting H to OH. Moreover, the OH radicals reacted with H₂, whereas the H radicals did not reduce H₂. It was shown that OH radicals formed by CO₂ reactivity were not suitable for H₂ formation. As for pulverized coal combustion, the tendencies of CH₄, CO, and H₂ formation in pulverized coal combustion were almost the same as those in the CH₄ flat flame.     

Photoelectrochemical characterization of the Cu(In,Ga)S2 thin film prepared by evaporation

Cu(In,Ga)S₂ chalcopyrite thin films have been characterized in order to determine the band edges potential position for photoelectrolysis water splitting. These values are correlated with the atomic composition of the samples. The characterization includes structural and atomic composition of the films. Sputtering/Sulphurization technique was used to prepare the films using different types of Cu–Ga and In targets. According to the capacitance measurements all of the films tested were p-type and the photoresponse technique shows that the band-gap values are between 1.38 and 1.74 eV. We distinguish three type of samples, low, medium and high content of Ga in the films, and the band edges potential position values depend on the amount of Ga in the films and also these values shift more positive when the pH of solution increases.     

Near-band-edge photoluminescnce in Cu(In,Ga)Se2 solar cells

Photoluminescence (PL) and PL decay characteristics of the near-band-edge (NBE) PL at room temperature have been studied on the Cu(In,Ga)Se₂ (CIGS) solar cells. The carrier recombination process has been discussed with emphasis on the photovoltaic properties of the solar cell. It has been found that: (i) PL intensity of the CIGS solar cells is much stronger than that in the corresponding CIGS thin films, (ii) the PL decay time of the cell is longer than that of the CIGS film, and (iii) the PL decay time of the CIGS solar cell exhibits strong dependence on the PL excitation intensity. In the CIGS solar cell, intense PL is obtained under the open circuit condition (oc), in contrast to the very low PL yield under the short circuit (sc) condition. The PL decay time under the sc condition is much shorter than that under the oc condition. Excitation intensity dependence of PL intensity and the PL decay time have been studied, and they are discussed with relation to the photo-voltage due to the PL excitation light. PL and injection EL under the external DC bias have been studied. The mapping image of NBE-PL intensity has been compared with that of the laser beam induced current (LBIC), and the PL intensity image reflects the photovoltaic properties of the CIGS solar cells. We demonstrated that NBE-PL of the CIGS solar cell reflects the photovoltaic effect, and it can be utilized as a powerful characterization method.     

Preparation of Cu(In,Ga)(S,Se)2 thin films by sequential evaporation and annealing in sulfur atmosphere

Cu(In,Ga)(S,Se)₂ thin films with high Ga/III ratio (around 0.8) were prepared by sequential evaporation from CuGaSe₂, CuInSe₂, In₂Se₃ and Ga₂Se₃ compounds and then annealing in H₂S gas atmosphere. The annealing temperature was varied from 400 to 500 °C. These samples were characterized by means of XRF, EPMA, XRD and SEM. The S/(S+Se) mole ratio in the thin films increased with increase in the annealing temperature, keeping the Cu, In and Ga contents nearly constant. The open circuit voltage increased and the short circuit current density decreased with increase in the annealing temperature. The best solar cell using Cu(In,Ga)(S,Se)₂ thin film with Ga/(In+Ga)=0.79 and S/(S+Se)=0.11 annealed at 400 °C demonstrated V_oc=535 mV, I_sc=13.3 mA/cm², FF=0.61 and efficiency=4.34% without AR-coating.     

Visible-light-driven ZnIn2S4/CdIn2S4 composite photocatalyst with enhanced performance for photocatalytic H2 evolution

ZnIn₂S₄/CdIn₂S₄ composite photocatalysts (x = 0–1) were successfully synthesized via a hydrothermal route. Compositions of ZnIn₂S₄/CdIn₂S₄ composite photocatalysts were optimized according to the photocatalytic H₂ evolution rate. XRD patterns indicate the as-prepared samples are mixtures of hexagonal and cubic structures. FESEM and TEM images show that the as-prepared samples are composed of flower-like microspheres with wide distribution of diameter. There is obviously distinguishing distribution of Zn, Cd elements among the composite architectures. UV–vis absorption spectra of different compositions exhibit that absorption edges of ZnIn₂S₄/CdIn₂S₄ composites slightly move towards longer wavelengths with the increment of CdIn₂S₄ component. A typical time course of photocatalytic H₂ evolution from an aqueous Na₂SO₃ and Na₂S solution over unloaded and PdS-loaded ZnIn₂S₄/CdIn₂S₄ composite photocatalyst is carried out. The initial activity for H₂ evolution over 0.75 wt% PdS-loaded sample is up to 780 μmol h⁻¹. And the activity of unloaded sample also reaches 490 μmol h⁻¹ with consistent stability.