Growth and properties of single-phase γ-In2Se3 thin films on (1 1 1) Si substrate by AP-MOCVD using H2Se precursor

A set of In₂Se₃ films was grown on (1 1 1) Si substrate with AlN buffer by metalorganic chemical vapor deposition (MOCVD) using H₂Se as the metalogramic precursors for Se. The In₂Se₃ films on (1 1 1) Si substrate were pinhole-free with homogeneous and lamellar structures. It was found that by properly controlling the substrate temperatures, single-phase γ-In₂Se₃ films with fairly good optical properties can be well fabricated. Photoluminescence spectra of single-phase γ-In₂Se₃ show exciton emissions at 2.140 eV at 10 K. The band gap of single-phase γ-In₂Se₃ at room temperature is estimated at 1.943 eV.     

Novel cobalt-free cathode materials BaCexFe1−xO3−δ for proton-conducting solid oxide fuel cells

A series of cobalt-free and low cost BaCe_xFe_1−xO_3−δ (x = 0.15, 0.50, 0.85) materials are successful synthesized and used as the cathode materials for proton-conducting solid oxide fuel cells (SOFCs). The single cell, consisting of a BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BaCe_xFe_1−xO_3−δ cathode layer, is assembled and tested from 600 to 700 °C with humidified hydrogen (3% H₂O) as the fuel and the static air as the oxidant. Within all the cathode materials above, the cathode BaCe_0.5Fe_0.5O_3−δ shows the highest cell performance which could obtain an open-circuit potential of 0.99 V and a maximum power density of 395 mW cm⁻² at 700 °C. The results indicate that the Fe-doped barium cerates can be promising cathodes for proton-conducting SOFCs.     

Characterization of Pr1−xSrxCo0.8Fe0.2O3−δ (0.2 ≤ x ≤ 0.6) cathode materials for intermediate-temperature solid oxide fuel cells

Cathode materials consisting of Pr_1−xSr_xCo_0.8Fe_0.2O_3−δ (x = 0.2–0.6) were prepared by the sol–gel process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples had an orthorhombic perovskite structure. The electrical conductivities were all higher than 279 S cm⁻¹. The highest conductivity, 1040 S cm⁻¹, was found at 300 °C for the composition x = 0.4. Symmetrical cathodes made of Pr_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (PSCF)–Ce_0.85Gd_0.15O_1.925 (50:50 by weight) composite powders were screen-printed on GDC electrolyte pellets. The area specific resistance value for the PSCF–GDC cathode was as low as 0.046 Ω cm² at 800 °C. The maximum power densities of a cell using the PSCF–GDC cathode were 520 mW cm⁻², 435 mW cm⁻² and 303 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively.     

Photovoltaic properties and technological aspects of In1−xGaxN/Si, Ge (0<x<0.6) heterojunction solar cells

Photovoltaic properties of n-In_1−xGa_xN/p-Si, Ge (IGN) heterostructures, covering the compositional range 0<x<0.6, have been evaluated by 1d device simulation, and are compared with the performance of c-Si homojunction thin film cells. Film morphology and physical properties were characterized by high-resolution transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) and photoluminescence (PL). Best achievable cell performances under AM1.5 illumination conditions were 18% for p-Ge, and up to 27% for n-IGN/p-Si contacts, achievable under optimum cell design, materials and operation parameters. Pure InN bottom layers, exhibiting an intrinsic band gap of 0.7 eV, reveal a reduced efficiency of 2.5%. The cell efficiency is strongly affected by film quality, accounted for by variation of electron affinity, majority carrier mobility, minority carrier lifetime, film thickness and doping levels. The morphology of thin IGN and InN films deposited onto silicon and sapphire substrate material revealed granular growth, along with a high density of grain boundaries. TEM resolved the formation of a very thin homogeneous silicon nitride interlayer on silicon substrates. The electrically isolating layer almost completely suppresses the photovoltaic effect. Depth profiling of InN films deposited onto sapphire substrates by SIMS analysis indicated oxygen as the dominant material contamination. It accounts, among other effects, for a gradually increasing band gap throughout the film structure. Observed large photoluminescence broadening effects, and related short minority carrier lifetimes are most likely related to high levels of oxygen contamination and concentration of grain boundaries. Possible routes to overcome these problems are discussed.     

The “artificial ostrich eggshell” project: Sterilizing polymer foils for food industry and medicine

We tried to produce antibacterial and antifouling advanced packing materials and medical plasters using the nowadays-available synthetic polymer foils. For this sake, we irradiated 10-μm-thick polyethylene terephthalate (PET) and polyimide (PI) foils with energetic ions at our heavy ion accelerators in Dubna or Berlin up to fluences around 10⁷ cm⁻² and etched them subsequently so that conical tracks with diameters in the order of a few micrometer emerged. The inner walls of these tracks were coated with bilayer structures of the composition: {SiO₂ nanoclusters and TiO₂ nanoclusters} or {Ag films and TiO₂ nanoclusters}. The nanoclustered layers with typical cluster sizes of 50–100 nm were formed by deposition of corresponding commercial colloidal solutions and subsequent baking.Upon presence of moisture and near UV light, the TiO₂ acts as a photoactive OH radical producer and electron scavenger. This destroys any organic matter passing through the ion tracks towards H₂O and CO₂—this may be an organic gas such as ethylene vapor (important to prevent premature food ripening), or fungi, viruses, bacteria, or other microorganisms (important for sterilization). The underlying SiO₂ or Ag layers prevent the polymeric substrate from being attacked by the TiO₂. Furthermore, the Ag layer enhances the antibacterial activity due to the toxicity of the Ag⁺ ions.     

Preparation of dense and uniform La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) films for fundamental studies of SOFC cathodes

Thin films of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) were deposited on (1 0 0) silicon and on GDC electrolyte substrates by rf-magnetron sputtering using a single-phase oxide target of LSCF. The conditions for sputtering were systematically studied to get dense and uniform films, including substrate temperature (23–600 °C) background pressure (1.2 × 10⁻² to 3.0 × 10⁻² mbar), power, and deposition time. Results indicate that to produce a dense, uniform, and crack-free LSCF film, the best substrate temperature is 23 °C and the argon pressure is 2.5 × 10⁻² mbar. Further, the electrochemical properties of a dense LSCF film were also determined in a cell consisting of a dense LSCF film (as working electrode), a GDC electrolyte membrane, and a porous LSCF counter electrode. Successful fabrication of high quality (dense and uniform) LSCF films with control of thickness, morphology, and crystallinity is vital to fundamental studies of cathode materials for solid oxide fuel cells.     

A potential interconnect material for solid oxide fuel cells: Nd0.75Ca0.25Cr0.98O3−δ

Chromium-deficient Nd_0.75Ca_0.25Cr_1−xO_3−δ (0.02 ≤ x ≤ 0.06) oxides are synthesized and assessed as a novel ceramic interconnect for solid oxide fuel cells (SOFCs). At room temperature, all the samples present single perovskite phase after sintering at 1600 °C for 10 h in air. Cr-deficiency significantly improves the electrical conductivity of Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides. No structural transformation occurs in the Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides in the temperature range studied. Among all the samples, the Nd_0.75Ca_0.25Cr_0.98O_3−δ sample with a relative density of 96.3% exhibits the best electrical conductivity of 39.0 and 1.6 S cm⁻¹ at 850 °C in air and hydrogen, respectively. The thermal expansion coefficient of Nd_0.75Ca_0.25Cr_0.98O_3−δ sample is 9.29 × 10⁻⁶ K⁻¹ in the temperature range from 30 to 1000 °C in air, which is close to that of 8 mol% yttria stabilized zirconia electrolyte (10.3 × 10⁻⁶ K⁻¹) and other cell components. The results indicate that Nd_0.75Ca_0.25Cr_0.98O_3−δ is a potential interconnect material for SOFCs.     

An analytical approach for optimising a set of α and ε values for solar energy applications

An analytical method for optimising a set of α and ε values for specified set of operating conditions (plate temperature, ambient temperature, number of glass covers, wind velocity, solar flux etc.) has been proposed. The absorptivity (α)-emissivity (ε) curves obtained suggest the existence of an optimum (α, ε) set, which would maximise the useful energy from a collector.     

High-efficiency μc-Si/c-Si heterojunction solar cells

P-type microcrystalline silicon (μc-Si (p)) on n-type crystalline silicon (c-Si(n)) heterojunction solar cells is investigated. Thin boron-doped μc-Si layers are deposited by plasma-enhanced chemical vapor deposition on CZ-Si and the V_oc of μc-Si/c-Si heterojunction solar cells is higher than that produced by a conventional thermal diffusion process. Under the appropriate conditions, the structure of thin μc-Si films on (1 0 0), (1 1 0), and (1 1 1) CZ-Si is ordered, so high V_oc of 0.579 V is achieved for 2×2 cm² μc-Si/multi-crystalline silicon (mc-Si) solar cells. The epitaxial-like growth is important in the fabrication of high-efficiency μc-Si/mc-Si heterojunction solar cells.     

Promotion on electrochemical performance of Ba‐deficient Ba1 − xBi0.05Co0.8Nb0.15O3 − δ cathode for intermediate temperature solid oxide fuel cells

Reducing the operating temperature is the developing trend for solid oxide fuel cells. The key is to develop the cathode with high electrocatalytic activity for oxygen reduction reaction operated at reduced temperatures. Ba‐deficient Ba_1 ? xBi_0.05Co_0.8Nb_0.15O_3 ? δ (Ba_1 ? xBCN, 0 ≤ x ≤ 0.10) are synthesized by solid‐state reaction method and evaluated as novel cathodes for intermediate‐temperature solid oxide fuel cells. Ba_1 ? xBCN is preserved to primitive cubic perovskite phase and meets the compatibility requirement with gadolinium doped ceria oxide (GDC) electrolyte at 950°C. Though the Ba deficiency distorts the cell symmetry, it improves the charge transfer steps rapidly, ascribing to the improvement of oxygen vacancy concentration. The polarization resistance of Ba_0.95BCN is as low as 0.056 Ω cm² in air at 700°C. The peak power density of the single cell with this cathode is as high as 1.41 W cm^?2 at 750°C with wet H₂ as fuel and air as oxidant, indicating the great potential for enhanced performance of Co‐based cathodes with A‐site deficiency.     

Structural stability of chemically delithiated layered (1 − z)Li[Li1/3Mn2/3]O2–zLi[Mn0.5−yNi0.5−yCo2y]O2 solid solution cathodes

Lithium has been chemically extracted from the layered oxide solid solutions Li[Li_1/3Mn_2/3]O₂–(z)Li[Mn_0.5−yNi_0.5−yCo_2y]O₂ (0 ≤ y ≤ 1/2 and 0.25 ≤ z ≤ 0.75) and characterized by X-ray diffraction. The weak super lattice reflections that occur in the parent samples at around 2θ = 20–25° vanish on extracting a significant amount of lithium due to the removal of lithium from the transition metal layer and a consequent loss of the ordering between the Li⁺ and the transition metal ions. Additionally, the chemical delithiation process results in an incorporation of some protons from the chemical delithiation medium into the layered lattice, which has an influence on the structure of the delithiated samples. While the incorporation of a higher concentration (0.4 per formula unit) of protons results in the formation of O1 or P3 phases, delithiated samples with <0.2 protons maintain the initial O3 structure. However, the electrochemically charged samples maintain the initial O3 structure.     

Synthesis and assessment of La0.8Sr0.2ScyMn1−yO3−δ as cathodes for solid-oxide fuel cells on scandium-stabilized zirconia electrolyte

Perovskite-type La_0.8Sr_0.2Sc_yMn_1−yO_3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc³⁺ into the B-site of La_0.8Sr_0.2MnO_3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc³⁺ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only 0.094 Ω cm² after a current passage of 400 mA cm⁻² for 30 min, significantly lower than that of LSM (0.25 Ω cm²). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm⁻² at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm⁻² under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.     

Electrical properties of ceria Co-doped with Sm and Nd

Ceria co-doped with Sm³⁺ and Nd³⁺ powders are successfully synthesized by citric acid–nitrate low-temperature combustion process. In order to optimize the electrical properties of the series of ceria co-doped with Sm³⁺ and Nd³⁺, the effects of co-doping, doping content and sintering conditions on grain and grain boundary conductivity are investigated in detail. For the series of Ce_0.9(Sm_xNd_1−x)_0.1O_1.95 (x = 0, 0.5, 1) and Ce_1−x(Sm_0.5Nd_0.5)_xO_δ (x = 0.05, 0.10, 0.15, 0.20) sintered under the same condition, Ce_0.9(Sm_0.5Nd_0.5)_0.1O_1.95 exhibits both higher grain and grain boundary conductivity. Compared with Ce_0.9Gd_0.1O_1.95 and Ce_0.8Sm_0.2O_1.9, Ce_0.9(Sm_0.5Nd_0.5)_0.1O_1.95 sintered at 1350–1400 °C shows higher total conductivity with the value of 1.0 × 10⁻² S cm⁻¹ at 550 °C. In addition, it can be found the trends of grain and grain boundary activation energies of Ce_1−x(Sm_0.5Nd_0.5)_xO_δ are both consistent with those of Ce_1−xNd_xO_δ, but different from those of Ce_1−xSm_xO_δ, which can be explained as: the local ordering of oxygen vacancies maybe occurs more easily in Nd-doped ceria than in Sm-doped ceria; the segregation amount of Sm³⁺ is more than that of Nd³⁺ to the grain boundaries in ceria co-doped with Sm³⁺ and Nd³⁺, which is confirmed by X-ray photoelectron spectroscopy (XPS).     

Modification of carbon aerogel supports for PEMFC catalysts

Nitrogen enriched carbon aerogels and Co-based non-noble metal catalysts supported on carbon aerogels have been synthesized and tested using XPS, HRTEM, XRD and RDE techniques. XPS spectra of unmodified carbon aerogels indicated a presence of two oxygen O(1s) groups and five carbon C(1s) groups in deconvoluted spectra. XPS spectra of chemically modified samples indicated nitrogen N(1s) introduced in the carbon aerogel structure by acidic (HNO₃) or basic (NH₄OH) chemical treatment.Synthesis of aerogel supported Co catalysts performed by using Co-methoxy-tetra-phenylporfirin as a macrocyclic compound incorporated into the aerogel structure, and sintered at 700 and 900 °C in N₂, revealed the presence of Co-metal nano-particles with 20 nm diameter. HRTEM and diffraction patterns show a β-Co FCC structure with many {111}<110> micro-twins in the Co nano-particles. The electrochemical properties of the synthesized catalysts in O₂-free and O₂-saturated sulfuric and perchloric acid solutions, evaluated by a rotating disc electrode (RDE) technique, demonstrated catalytic activity in hydrogen oxidation and oxygen reduction reactions.     

Characterization of the 75% Gd0.8Sr0.2CoO3−δ/25% Ce0.9Gd0.1O2−δ composite cathode system for use in intermediate temperature solid oxide fuel cells

The composite cathode system is examined for suitability on a Ce_0.9Gd_0.1O_2−δ electrolyte based solid oxide fuel cell at intermediate temperatures (500–700 °C). The cathode is characterized for electronic conductivity and area specific charge transfer resistance. This cathode system is chosen for its excellent thermal expansion match to the electrolyte, its relatively high conductivity (115 S cm⁻¹ at 700 °C), and its low activation energy for oxygen reduction (99 kJ mol⁻¹). It is found that the decrease of sintering temperature of the composite cathode system produces a significant decrease in charge transfer resistances to as low as 0.25 Ω cm². The conductivity of the cathode systems is between 40 and 88 S cm⁻¹ for open porosities of 30–40%.     

Improved quality a-SiC:H films prepared by photo chemical vapour decomposition of silane and acetylene

Hydrogenated amorphous and microcrystalline silicon carbon alloy films have been grown by photo-CVD using C₂H₂ as a source gas of carbon. The hydrogenated amorphous silicon carbon (a-SiC:H) film with a band gap of ~2.0 eV prepared at a very low hydrogen (LD) concentration exhibits better photo-electronic properties compared to that at high hydrogen dilution (HD) having a similar optical gap. Notwithstanding a high deposition rate, the high photosensitivity ( 10⁶), the low density of the defect states ( 6 × 10¹⁶cm⁻³) and the Urbach energy parameter (72 meV) for the a-SiC:H film prepared at low hydrogen dilution and pressure are impressive. On the other hand, low pressure along with high hydrogen dilution have been found to be conducive to microcrystalline silicon carbon alloy (μc-Si:H) formation. Interestingly, crystallites are of silicon while carbon remains in the amorphous and grain boundary regions.     

p-doped μc-Si:H window layers prepared by hot-wire CVD for amorphous solar cell application

We report on boron-doped μc-Si:H films prepared by hot-wire chemical vapor deposition (HWCVD) using silane as a source gas and trimethylboron (TMB) as a dopant gas and their incorporation into all-HW amorphous silicon solar cells. The dark conductivity of these films was in the range of 1–10 (Ω cm)⁻¹. The open circuit voltage V_oc of the solar cells was found to decrease from 840 mV at low hydrogen dilution H-dil=91% to 770 mV at high H-dil =97% during p-layer deposition which can be attributed to the increased crystallinity at higher H-dil and to subsequent band edge discontinuity between μc-Si:H p- and amorphous i-layer. The short circuit current density J_sc and the fill factor FF show an optimum at an intermediate H-dil and decrease for the highest H-dil. To improve the conversion efficiency and the reproducibility of the solar cells, an amorphous-like seed layer was incorporated between TCO and the bulk p-layer. The results obtained until now for amorphous solar cells with and without the seed layer are presented. The I–V parameters for the best p–i–n solar cell obtained so far are J_sc=13.95 mA/cm², V_oc=834 mV, FF=65% and η=7.6%, where the p-layers were prepared with 2% TMB. High open circuit voltages up to 847 mV could be achieved at higher TMB concentrations.     

Effects of cyclic carbonates as additives to γ-butyrolactone electrolytes for rechargeable lithium cells

γ-Butyrolactone (GBL) has a high boiling point, a low freezing point, a high flashing point, a high dielectric constant and a low viscosity. GBL is a very preferable solvent for lithium ion batteries. However, GBL readily undergoes reductive decomposition on the surface of the negative electrodes, and it forms a solid electrolyte interphase (SEI) with a large resistance. It is causing deterioration of battery performances. In this work, effects of cyclic carbonates as additives to GBL electrolytes were investigated. As these carbonates, ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), vinylethylene carbonate (VEC), and phenylethylene carbonate (PhEC) were investigated using LiCoO₂/graphite cells. The effects of these additives were evaluated from the viewpoints of improvement of the battery performance and suppression of the reductive decomposition of GBL. VC, VEC and PhEC were effective to suppress the excess reductive decomposition of GBL. Battery performances were improved and the following results were obtained from the electrochemical measurements of LiCoO₂/graphite cells with GBL-based electrolytes. Residual capacity was high in the order of VEC > VC > PhEC. Rate capability was high in the order of PhEC > VC > VEC. These additives have advantages and disadvantages. By optimizing electrolyte formulation, the performances of Li-ion batteries using GBL-based electrolytes will be improved further.     

ZnO-doped BaZr0.85Y0.15O3−δ proton-conducting electrolytes: Characterization and fabrication of thin films

ZnO-doped BaZr_0.85Y_0.15O_3−δ perovskite oxide sintered at 1500 °C has bulk conductivity of the order of 10⁻² S cm⁻¹ above 650 °C, which makes it an attractive proton-conducting electrolyte for intermediate-temperature solid oxide fuel cells. The structure, morphology and electrical conductivity of the electrolyte vary with sintering temperature. Optimal electrochemical performance is achieved when the sintering temperature is about 1500 °C. Cathode-supported electrolyte assemblies were prepared using spin coating technique. Thin film electrolytes were shown to be dense using SEM and EDX analyses.     

High-rate microcrystalline silicon deposition for p–i–n junction solar cells

We have developed a high-rate plasma process based on high-pressure and silane-depletion glow discharge for highly efficient microcrystalline silicon (μc-Si:H) p–i–n junction solar cells. Under high-rate conditions (2–3 nm/s), we find that the deposition pressure becomes the dominant parameter in determining solar-cell performance. With increasing deposition pressure from 4 to 7–9 Torr, short-circuit current increases by 50% due to a remarkable improvement in quantum efficiencies at the visible and near infrared. As a result, the maximum efficiency of 9.13% has been achieved at an i-layer deposition rate of 2.3 nm/s. We attribute the improved performance of high-pressure-grown μc-Si:H solar cells to the structural evolution toward denser grain arrangement that prevents post-oxidation of grain boundaries.