Earth-abundant photovoltaic semiconductor NaSbS_2 in the rocksalt-derived structure:A first-principles study

NaSbS_2 was recently proposed as a novel photovoltaic semiconductor with earth-abundant component elements,but its fundamental material properties have not been well studied.The systematical first-principles calculations for its electronic,optical and defect properties were carried out in the present study,and the results show that:i)NaSbS_2 in the rocksalt-derived structure has a quasi-direct band gap and thus may have long minority carrier lifetime;ii) its absorption coefficients are as high as 10~4～10~5 cm~(-1) for the visible light and almost isotropic despite that the structure is distorted relative to the high-symmetry rocksalt structure;iii) the effective masses of the electron and hole carriers are anisotropic with much larger values along the z direction than in the x-y plane,and hence the orientational control of thin films should be important for enhancing the photovoltaic performance;iv) the valence and conduction band edges of NaSbS_2 are close to those of CuGaSe_2) so the n-CdS/pCuGaSe_2 device structure can be inherited to form the n-CdS/p-NaSbS_2 solar cells;v) the acceptor defects (Na_(Sb)antisites and Na vacancies) have very high concentration,making the synthesized NaSbS_2 always be p-type;vi)the S-rich condition can suppress the formation of deep-level donor defects (S vacancies and Sb_(Na) antisites) and therefore should be adopted for fabricating high-efficiency NaSbS_2 solar cells.     

Comparison between P25 and anatase-based TiO_2 quasi-solid state dye sensitized solar cells

Pure anatase TiO2 films have been made via hydration of titanium isopropoxide using a sol-gel tech- nique, while mixed TiO2 films which contained both anatase and rutile TiO2 were made from commercial P25 powder. Quasi-solid state dye-sensitized solar cells were fabricated with these two kinds of mesoporous films and a comparison study was carried out. The result showed that the open-circuit photovoltages (Voc) for both kinds of cells were essentially the same, whereas the short-circuit photo- currents (Isc) of the anatase-based cells were about 33% higher than that of the P25-based cells. The highest photocurrent intensity of the anatase-based cell was 6.12 mA/cm2 and that of the P25-based cell was 4.60 mA/cm2. Under an illumination with the light intensity of 30 mW/cm2, the corresponding en- ergy conversion efficiency was measured to be 7.07% and 6.89% for anatase-based cells and P25-based cells, respectively.     

Recent Advances in High Efficiency Solar Cells

1 Results The conversion efficiency of sunlight to electricity is limited around 25%,when we use single junction solar cells. In the single junction cells,the major energy losses arise from the spectrum mismatching. When the photons excite carriers with energy well in excess of the bandgap,these excess energies were converted to heat by the rapid thermalization. On the other hand,the light with lower energy than that of the bandgap cannot be absorbed by the semiconductor,resulting in the losses. One way of reducing these losses is fabricating tandem or stacked solar cells. Merely stacking the more number of cells with different bandgap can increase the conversion efficiency. III-V compound multi-junction solar cells,such as InGaP/GaAs/Ge,have the potential for achieving high conversion efficiencies that are promising for space and terrestrial applications. One of the important issues for realizing the high conversion efficiency is the optically and electrically low-loss interconnection of each sells. A degenerately impurity doped tunnel junction,which is thin and wide-bandgap,is an attractive one,and a double hetero structure is useful for preventing impurity diffusion during the overgrowth of the top cell. Another issue is a lattice matching. Since there is a slightly difference in the lattice constant between Ge substrate and GaAs,the misfit dislocations are generated in thick GaAs layers and the electrical properties degrade. To prevent this problem,InGaAs is applied as a middle cell material,which is lattice matching to the Ge substrate. So far,the conversion efficiency of InGaP/InGaAs/Ge has been improved up to 29%-30% (AM0) and 31.7% (AM1.5G). The concentrator cells achieved the higher conversion efficiency up to 40.7% under 240 suns. For realizing a future multi-junction solar cell with ultra-high performance,InGaAsN and related materials are investigated,because it can be grown lattice matched to GaAs with a band gap in the range of 0.9-1.4 eV. When we adopt the InGaP/GaAs/InGaAsN/Ge structure as a four-junction solar cell,the efficiency over 40% (AM1.5G) will be expected. However,the minority carrier diffusion length in the present InGaAsN crystal is too short to realize the tandem solar cells with the expected high performance. To solve this problem,we have been developing the chemical beam epitaxy (CBE) method for achieving InGaAsN with good quality. The films are grown using organic gas molecules as sources under a high vacuum condition (10-2 Pa). Because of the ultra low pressure,the reactions between the source gases in the gas phase are suppressed and the chemical reactions occur only on a growing surface,which allow using active source gases that decompose at low temperatures. GaAsN thin films are grown using monomethylhydrazine as a N source with narrow X-ray diffraction peaks at growth temperatures in the 380-420 ℃ range. In the present talk,we will review the progress of high conversion efficiency tandem-solar cells and discuss some of our recent results.     

Comparison between P25 and anatase-based TiO<Subscript>2</Subscript> quasi-solid state dye sensitized solar cells

Pure anatase TiO2 films have been made via hydration of titanium isopropoxide using a sol-gel tech-nique, while mixed TiO2 films which contained both anatase and rutile TiO2 were made from commercial P25 powder. Quasi-solid state dye-sensitized solar cells were fabricated with these two kinds of mesoporous films and a comparison study was carried out. The result showed that the open-circuit photovoltages （Voc） for both kinds of cells were essentially the same, whereas the short-circuit photo-currents （1sc） of the anatase-based cells were about 33% higher than that of the P25-based cells. The highest photocurrent intensity of the anatase-based cell was 6.12 mA/cm^2 and that of the P25-based cell was 4.60 mA/cm^2. Under an illumination with the light intensity of 30 mW/cm^2, the corresponding energy conversion efficiency was measured to be 7.07% and 6.89% for anatase-based cells and P25-based cells, respectively.     

Electrochemical reversibility of magnesium deposition-dissolution on aluminum substrates in Grignard reagent/THF solutions

The electrochemical behavior of magnesium deposition-dissolution on scratched aluminum foils in Grignard reagent/tetrahydrofuran (THF) solutions (1 mol L-1 EtMgBr/THF), which is regarded as a potential electrolyte of rechargeable magnesium batteries, was studied by using various methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge (deposition-dissolution) tests. The results present that the obtained magnesium deposits do not exhibit the morphology of dendrite and the Mg-Al alloy is not found on the surface of aluminum foils. The magnesium deposited on the aluminum substrates have excellent electrochemical cyclic performance in 1 mol L-1 EtMgBr/THF solution. The aluminum can be used as a candidate material of the negative current collector for rechargeable magnesium batteries.     

Study of ionizable drugs transfer across the water／1,2-dichloroethane interface with phase volume ratio equal to unity using a three-electrode system

The electrochemical behavior of ionizable drugs (Amitripty/ine, Diphenhydramine and Trihexyphenedyl) at the water/1,2-dichloroethane interface with the phase volume ratio (r=Vo/Vw) equal to 1 are investigated by cyclic voltammetry. The system is composed of an aqueous droplet supported at an Ag/AgCI disk electrode and it was covered with an organic solution. In this manner, a conventional three-electrode potentiostat can be used to study the ionizable drugs transfer process at a liquid/liquid interface.Physicochemical parameters such as the formal transfer potential, the Gibbs energy of transfer and the standard partition coefficients of the ionized forms of these drugs can be evaluated from cyclic voltammograms obtained. The obtained results have been summarized in ionic partition diagrams, which are a useful tool for predicting and interpreting the transfer mechanisms of ionizable drugs at the liquid/liquid interfaces and biological membranes.     

Electrochemical characterization of MnO2 as the cathode material for a high voltage hybrid capacitor

Manganese dioxide (MnO₂) was prepared using the ultrasonic method. Its electrochemical performance was evaluated as the cathode material for a high voltage hybrid capacitor. And the specific capacitance of the MnO₂ electrode reached 240 F·g-1. The new hybrid capacitor was constructed, combining A1/Al₂O₃ as the anode and MnO₂ as the cathode with electrolyte for the aluminum electrolytic capacitor to solve the problem of low working voltage of a supercapacitor unit. The results showed that the hybrid capacitor had a high energy density and the ability of quick charging and discharging according to the electrochemical performance test. The capacitance was 84.4 μF, and the volume and mass energy densities were greatly improved compared to those of the traditional aluminum electrolytic capacitor of 47 μF. The analysis of electrochemical impedance spectroscopy (EIS) showed that the hybrid capacitor had good impedance characteristics.     

γ射线还原的氧化石墨烯的电学、热学和电化学性能

The properties of γ-ray-reduced graphene oxide samples (GRGOs) were compared with those of hydrazine hydrate-reduced graphene oxide (HRGO). Fourier transform infrared spectroscopy, X-ray diffractometry, Raman spectroscopy, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, electrometry, and cyclic voltammetry were carried out to verify the reduction process, structural changes, and defects of the samples, as well as to measure their thermal, electrical, and electrochemical properties. Irradiation with γ-rays distorted the structure of GRGOs and generated massive defects through the extensive formation of new smaller sp2-hybridized domains compared with those of HRGO. The thermal stability of GRGOs was higher than that of HRGO, indicating the highly efficient removal of thermally-labile oxygen species by γ-rays. RRGO prepared at 80 kGy showed a pseudocapacitive behavior comparable with the electrical double-layer capacitance behavior of HRGO. Interestingly, the specific capacitance of GRGO was enhanced by nearly three times compared with that of HRGO. These results reflect the advantages of radiation reduction in energy storage applications.     

Insight into the covalent grafting of organic films onto carbon steel surfaces for protection

The novel use of p-nitrophenyldiazonium tetrafluoroborate salt(GG salt)as a protectant that is electrochemically grafted onto carbon steel has been investigated in0.05 mol L-1H2SO4and 5 wt%NaCl solutions using various corrosion monitoring techniques,such as electrochemical impedance spectroscopy,potentiodynamic polarisation,infrared spectra and scanning electron microscopy measurements.The electrochemical study reveals that this compound is a mixed inhibitor that predominantly controls the cathodic reaction.The surface-grafted film decreases the double-layer capacitance and obviously increases the charge transfer resistance relative to a bare carbon electrode.The values of inhibition effect remain nearly unchanged with an increase in temperature range of 298–318 K.The aryl diazonium is covalently bonded on the steel surface,causing a slight decrease in the apparent activation energy.Overall,the surface-grafted films exhibit excellent inhibition performance in acid and saline solutions within the studied temperature range.     

CHARACTERIZATION ON DOPING POLYPYRROLE FILMS

The conductivity of polypyrrole films has been enhanced by electrochemical post-deposition doping with various anions. The change of conductivity was found to depend on the type and concentration of the anion. Results for the polypyrrole films doped with anions of H_2SO_4,,(C_2H_5)_4, N(O_3 SC_6H_4CH_3), KI,CH_3 C_6H_4 SO_3 H·H_2O(p-Toluene Sulfonic acid Monohydydrate), AlCl_3, KBrO_3 and HNO_3 showed that in the case of H_2 SO_4, (C_2H_5)_4 N(O_3SC_6 H_4 CH_3)and CH_3C_6H_4SO_3H·H_2O the conductivity can be enhanced by up to a factor of two, from a value of 67 sem~(-1) up to 165, 102 and 95 s cm~(-1), respectively. Doping with I~- had a negligible effect on the conductivity which was about 71 s cm~(-1), while in the case of AlCl_3, KBrO_3 and HNO_3 the conductivity of the polypyrrole decreased significantly for certain anion concentrations.     

Pulsed laser deposited Al-doped ZnO thin films for optical applications

Highly transparent and conducting Al-doped Zn O(Al:Zn O) thin films were grown on glass substrates using pulsed laser deposition technique.The profound effect of film thickness on the structural, optical and electrical properties of Al:Zn O thin films was observed. The X-ray diffraction depicts c-axis, plane(002) oriented thin films with hexagonal wurtzite crystal structure. Al-doping in Zn O introduces a compressive stress in the films which increase with the film thickness. AFM images reveal the columnar grain formation with low surface roughness. The versatile optical properties of Al:Zn O thin films are important for applications such as transparent electromagnetic interference(EMI) shielding materials and solar cells. The obtained optical band gap(3.2–3.08 e V) was found to be less than pure Zn O(3.37 e V) films. The lowering in the band gap in Al:Zn O thin films could be attributed to band edge bending phenomena. The photoluminescence spectra gives sharp visible emission peaks, enables Al:Zn O thin films for light emitting devices(LEDs) applications. The current–voltage(I–V) measurements show the ohmic behavior of the films with resistivity(ρ) 10-3Ω cm.     

Understanding supercapacitors based on nano-hybrid materials with interfacial conjugation

The recent fast development of supercapacitors,also known scientifically as electrochemical capacitors,has benefited significantly from synthesis,characterisations and electrochemistry of nanomaterials.Herein,the principle of supercapacitors is explained in terms of performance characteristics and charge storage mechanisms,i.e.double layer(or interfacial) capacitance and pseudo-capacitance.The semiconductor band model is applied to qualitatively account for the pseudo-capacitance in association with rectangular cyclic voltammograms(CVs) and linear galvanostatic charging and discharging plots(GCDs),aiming to differentiate supercapacitors from rechargeable batteries.The invalidity of using peak shaped CVs and non-linear GCDs for capacitance measurement is highlighted.A selective review is given to the nano-hybrid materials between carbon nanotubes and redox active materials such as electronically conducting polymers and transition metal oxides.A new concept,"interfacial conjugation",is introduced to reflect the capacitance enhancement resulting from π-π stacking interactions at the interface between two materials with highly conjugated chemical bonds.The prospects of carbon nanotubes and graphenes for supercapacitor applications are briefly compared and discussed.Hopefully,this article can help readers to understand supercapacitors and nano-hybrid materials so that further developments in materials design and synthesis,and device engineering can be more efficient and objective.     

Characterization and corrosion studies of ternary Zn–Ni–Sn alloys

Nine distinct zinc-nickel-tin films with different compositions have been galvanostatically electrodeposited. The films have been characterized by scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS). Their corrosion potentials and densities have been estimated using Tafel extrapolation. Next, the electrochemical behaviors of the films(deposited through the electrolytes containing 0, 6, 8, and10 g/L SnCl_2?6H_2O) have been examined based on cyclic voltammetry(CV) measurements. Further, these films have been immersed in 3.5 wt%Na Cl solution for 1 h, 1 d, 7 d, 14 d, 28 d, and 42 d followed by application of Tafel extrapolation and electrochemical impedance spectroscopy(EIS) tests on each aged sample. Finally, to analyze the morphologies and the compositions of the oxide films covering the surfaces of the 42-d aged films, FT-IR and SEM analyses have been performed. The results indicated that the Zn–Ni–Sn film produced through the bath including 6g/L SnCl_2?6H_2 O exhibits superior corrosion resistance because of the high Ni content in the presence of Sn that promotes the barrier protection capability of the deposit.     

Development of multi-functional nano-paint for energy harvesting applications

The multi-functionality of lead magnesium niobate-lead titanate/paint(PMN-PT/paint) nanocomposite films for energy harvesting via piezoelectric and pyroelectric effects is described. PMN-PT/paint films have been fabricated by a conventional paint-brushing technique to provide a low-cost, low-temperature and low–energy route to create multi-functional films. The properties investigated included dielectric constants, ε' and ε', as a function of temperature, frequency and composition. From these parameters, it is indicated that the dielectric constants and AC conductivity(σ_(AC)) increase with an increase of filler content and temperature, implying an improvement of the functionality of the films. The results revealed that σ_(AC) obeyed the relation σ_(AC) =Aω~s, and exponents, was found to decrease by increasing the temperature. The correlated barrier hopping was the dominant conduction mechanism in the nanocomposite films. The efforts were made to investigate the performance of nanocomposite films to mechanical vibrations and thermal variations. A cantilever system was designed and examined to assess its performance as energy harvesters. The highest output voltage and power for a PMN-PT/paint based harvester with a broad frequency response operating in the-31-piezoelectric mode were 65 mV and 1 nW, respectively.Voltage and power were shown to be enhanced by application of thermal variations. Thus, films could be utilized for combined energy harvesting via piezoelectric and pyroelectric characteristics.     

Effect of electrolytes on electrochemical properties of graphene sheet covered with polypyrrole thin layer

Graphene sheet (GS) was successfully covered with a polyp yrrole (PPy) thin layer through in situ chemical oxidative polymerization of pyrrole monomers in aqueous solution by using GS as a support materi al and ferric trichloride as an oxidant. The resulting nanocomposite was studied by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and electrical measurements, including cyclic voltammetry (CV), galvanostatic charge/discharge experiment (GCD), and impedance spectroscopy (EIS). It has been found that the nanocomposite exhibited a typically curved and layer ?like structure, and conformational change of PPy chains occurred due to the π?π stacking interaction between the graphitic structures in GS and aromatic rings of the PPy chains. More attention was paid to the effect of electrolytes on electrochemical properties of the nanocomposites, as expected, electrochemical performance was dependent on the nature of the electrolyte, and the neutral electrolytes containing alkali metal ions were found to be very suitable for GS/PPy nanocomposite. Compared with the pure PPy, the nanocomposite possessed larger specific capaci tance and lower internal im pedance, indicating that the nanocomposite can be a promising candidate as electrod e material for supercapacitors.     

An integrated nanocarbon–cellulose membrane for solid-state supercapacitors

In this work, we demonstrate the assembly of oxidised carbon nanohybrids(o CNHs) with a commercial cellulose membrane for solid-state supercapacitors. The o CNHs–cellulose membranes were prepared by filtering a water dispersion of o CNHs through the cellulose membrane. The o CNHs were derived from carbon nanotubes via a modified Hummer’s method and contained both closed tubes and unzipped tubes, which indicated a hybrid geometrical structure. The solid-state supercapacitor based on the o CNHs–cellulose membranes showed a high areal capacitance of *75 m F/cm~2 at a low scan rate(5 m V/s)and excellent stability for 1,000 cycles.     

Electrochemical exfoliation for few-layer graphene in molybdate aqueous solution and its application for fast electrothermal film

There are still serious barriers from laboratory exploration to large-scale production of commercializing highquality graphene, especially by environmental-friendly methods. In this study, a simple and efficient electrochemical method for the preparation of high-quality water-dispersible graphene has been developed using molybdate aqueous solutions as the electrolyte. The exfoliation of graphite paper could be achieved in the electrolyte with a high yield of a few layers graphene(1–5 layers, 76%) and uniform lateral size(1–6 μm, 90%).The as-obtained few layers graphene well dispersed in aqueous solution with a solubility of ～4 mg mL~(-1) and stability for at least 2 months. It provides a new green method to prepare high-quality graphene. The as-prepared water-dispersible graphene films exhibit significant electrothermal performance, with a steady-state temperature of 147 °C under voltage of 10 V and a maximum heating rate achieved of 11.8 °C s~(-1).     

Immobilization and direct electrochemistry of copper-containing enzymes on active carbon

Two typical and important copper-containing enzymes, laccase (Lac)and tyrosinase (Tyr), have been immobilized on the surface of active carbon with simple adsorption method. The cyclic voltammetric results indicated that the active carbon could promote the direct electron transfer of both Lac and Tyr and a pair of well-defined and nearly symmetric redox peaks appeared on the cyclic voltammograms of Lac or Tyr with the formal potential, E^0‘,independent on the scan rate. The further experimental results showed that the immobilized copper-containing oxidase displayed an excellent electrocatalytic activity to the electrochemical reduction of 02. The immobilization method presented here has several advantages, such as simplicity, easy to operation and keeping good activity of enzyme etc., and could be further used to study the direct electrochemistry of other redox proteins and enzymes and fabricate the catalysts for biofuel cell.     

Organolead halide perovskites: a family of promising semiconductor materials for solar cells

Great attention has recently been drawn to developing cost-effective, high efficiency solar cells to meet the ever increasing demand for clean energy. We have most recently witnessed a breakthrough and a rapid development in solid state, hybrid solar cells using or- ganolead halide perovskites as light harvesters. These semiconductors can not only serve as sensitizer in solid state sensitized solar cells with efficiency up to unprece- dented 15 %, but also function as both light absorber and hole conductor （or electron conductor） at the same time to display power conversion efficiency above 10 %. In this review, we will introduce their operation mechanism, structure, and especially the development of the organolead halide perovskite based solar cells. Based on the achieve- ments that have been made to date, solid state photovoltaic device with superior performance than the present one is highly expected.     

Preparation of nanocrystalline Co3O4 and its properties as supercapacitors

Nanocrystaitines Co3O4 with the particle diameter of 3 nm are prepared and tested as active electrode material for an electrochemical supercapacitor. The results of characterization indicate that the grain size of this material is very small; the specific surface area is very high (192m^2/g); the distributions of pore diameter are desirable and effective; furthermore, the agglomeration problem among small particles was solved to a certain extent. The electrochemical tests show that the electrode prepared with the Co3O4 exhibits distinct characteristic of capacitance and very high specific capacitance of 365-401 F/g. Additionally, the main attribute of capacitance, namely supercapacitance, was also testified.