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1.
Nanostructured thin films of undoped and Ag-doped cuprous oxide were deposited on indium tin oxide-coated glass substrate using simple spray pyrolysis method for their use as photocathode in photoelectrochemical (PEC) cell for solar energy based water splitting. Combination of experiments and first-principles density functional theory based calculations was used to determine and understand the effect of Ag substitution on electronic structure and PEC performance. Thin films were characterized using XRD, FE-SEM, UV–Vis spectroscopy and PEC measurements. The results of DFT calculations show that the top of valence band and bottom of conduction band of undoped Cu2O lie at Г point of brillouin zone, respectively, suggesting that pure Cu2O is a direct band gap material. Minimal changes appear in the band gap and band gap energies in the Ag-doped Cu2O system, keeping it still a direct band gap material. A defect band appearance can be seen between ?4 and ?5 eV in the valence band consisting mainly of Ag 4d states and can be explained by a stronger interaction between the Ag 4d and O 2p, due to the larger Ag size. Ag-doped samples exhibit improved conductivity and fourfold increase in photocurrent density with respect to undoped samples.  相似文献   

2.
Abstract

The electronic structure of polycrystalline C60 thin films has been investigated using surface photovoltage spectroscopy (SPS) and conductivity measurements. the films show n-type semiconductivity with an activation energy of ~ 0.8 eV as found from the temperature dependence of the conductivity at high temperatures. the electronic structure emerging from our SPS results comprises a 1.6 eV photo-conduction gap, a mobility gap of about 2.25 eV and two gap states, a donor and an acceptor, at 0.35 eV and (1.0-1.1) eV, respectively, below the photo-conduction edge. the results indicate the possibility of the existence of band tails, extending into the optical gap of these films, as well as other deep gap states.  相似文献   

3.
Cd2GeO4 crystallizes with an orthorhombic structure space group Pbnm (a = 5.20, b = 11.14, c = 6.57A) as determined by the onset of photocurrent, the flat band potential is ?0.80(5)V vs SCE. An indirect band gap at 3.15(5) eV and a direct band gap at 4.15(5) eV were ascertained from measurement of the photoelectronic quantum efficiency. Despite some initial loss in the photoresponse during the first hour of irradiation at 1.0 W/cm2, Cd2GeO4 has been shown to be far more stable as an electrode than Cd2SnO4.  相似文献   

4.
AgInSe2 (AIS) films were grown on n-type Si substrates by the ultra-high-vacuum pulsed laser deposition technique from the AIS target synthesized from high-purity materials. The X-ray diffraction and microscopic studies of the films show that films are textured having terrace-like surface morphology. The optical studies of the films show that the optical band gap is about 1.24 eV. The electrical conductivity of AgInSe2/Si films shows excellent diode characteristics. The photoconductivity of the AgInSe2/Si device shows photocurrent of 2.8 mA at a bias-voltage of − 1 V with an open circuit voltage of 0.15 V. This shows that AIS films are very good absorber material for solar cell technology.  相似文献   

5.
The coexistence of large conductivity and robust ferroelectricity is promising for high-performance ferroelectric devices based on polarization-controllable highly efficient carrier transport. Distinct from traditional perovskite ferroelectrics, Bi2WO6 with a layered structure shows a great potential to preserve its ferroelectricity under substantial electron doping. Herein, by artificial design of photosensitive heterostructures with desired band alignment, three orders of magnitude enhancement of the short-circuit photocurrent is achieved in Bi2WO6/SrTiO3 at room temperature. The microscopic mechanism of this large photocurrent originates from separated transport of electrons and holes in [WO4]−2 and [Bi2O2]+2 layers respectively with a large in-plane conductivity, which is understood by a combination of ab initio calculations and spectroscopic measurements. The layered electronic structure and appropriately designed band alignment in this layered ferroelectric heterostructure provide an opportunity to achieve high-performance and nonvolatile switchable electronic devices.  相似文献   

6.
Kousik Dutta 《Materials Letters》2007,61(27):4967-4971
Nanostructured tin dioxide (SnO2) is synthesized in the form of colloidal sol. Aniline monomer is polymerized in colloidal sol of SnO2 to prepare inorganic-organic hybrid nanocomposites. Optical band gap increases from 3.74 eV to 4.23 eV with increase of polyaniline concentration. The observed nonlinear current-voltage characteristics are satisfactorily explained using the Schottky type barriers. The temperature dependence of conductivity reveals three dimensional Mott's hopping process.  相似文献   

7.
Abstract

The optical properties of a-Se100-xSbx thin films (where x = 0, 0.5, 2.5, 5 and 10) have been studied in the wavelength range 540–900 nm. It was found that the optical band gap increases with increasing Sb concentration in the a-Se100-x Sb x system. The refractive index n decreases, while the extinction coefficient k increases with increasing photon energy. DC conductivity measurements of a-Se100-x Sb x thin films have been reported in the temperature range 349–375 K. It has been observed that the conductivity increases while the activation energy decreases with increasing Sb concentration. We correlated the optical band gap with the electronegativity of the sample. The band gap increases with the decrease in electronegativity of each sample of a-Se100-x Sb x .  相似文献   

8.
The electronic conductivity of Sr3-3xLa2xx(VO4)2 solid solutions was measured at oxygen pressures from 10-13 to 105 Pa and temperatures from 1070 to 1270 K, and their band gap was determined as a function of composition. The activation energy (≏2.85 eV) and enthalpies of electron generation (≏4.2 eV) and migration (≏0.75 eV) were determined. A correlation between the band gap and electronic conductivity of the solid solutions was revealed  相似文献   

9.
《材料科学技术学报》2019,35(8):1570-1577
Cuprous oxide (Cu2O) is an attractive material for photoelectrochemical (PEC) hydrogen production or photovoltaic application, because of its appropriate band gap, low material cost and non-toxic. In this paper, Cu2O films were obtained by comproportionation in acid cupric sulfate solutions with varying concentrations of potassium nitrate. Photoelectrochemical and electrochemical experiments, such as zero-bias photocurrent responses, voltammograms, and Mott-Schottky measurements, show that the Cu2O films grown in low (≤0.75 mol dm–3) and high (≥1.00 mol dm–3) nitrate ion concentrations presented n-type and p-type conductivity, respectively. Open circuit potential and polarization behavior were monitored to investigate the mechanism of modulating conductivity type. Nitrate ions consume protons in the plating solution during comproportionation with different concentrations of nitrate ions creating different pH at the Cu2O/solution interface. This gradient leads to the transformation of Cu2O films conductivity changing from n-type to p-type with increasing the concentration of nitrate ions in the plating solution. This method could be used to fabricate homojunction electrode on metal substrate for PEC hydrogen production or photoelectric application.  相似文献   

10.
Thin CdS films have been grown by chemical bath (CdCl2, thiourea, ammonia) deposition (CBD) on SnO2 (TO)-coated glass substrate for use as window materials in CdS/CdTe solar cells. High-resolution transmission electron microscopy revealed grains with an average size of 10 nm. The structure was predominantly hexagonal with a high density of stacking faults. The film crystallinity improved with annealing in air. Annealing in a CdCl2 flux increased the grain size considerably and reduced the density of stacking faults. The optical transmission of the as-deposited films indicated a band gap energy of 2.41 eV. Annealing in air reduced the band gap by 0.1 eV. Annealing in CdCl2 led to a sharper optical absorption edge that remained at 2.41 eV. Similar band gap values were obtained by photocurrent spectroscopy and electroabsorption spectroscopy (EEA) using an electrolyte contact. EEA spectra were broad for the as-deposited and air-annealed samples, but narrower for the CdCl2-annealed films, reflecting the reduction in stacking fault density. Donor densities of ca. 1017 cm –3 were derived from the film/electrolyte junction capacitance.  相似文献   

11.
The growth of Tl3SbS3 single crystal is reported for the first time. 5×1×1 cm3 ingots are obtained by using vertical Bridgmann method with a 2°C/mm gradient and a 0.7 mm/h growth rate. Intrinsic conductivity and photoconductivity are investigated. The weak dark conductivity, ~ 10?10cm)?1 at 300° K, contrasts with a strong photosensitivity. The value of the fundamental band gap deduced from spectral dependence of the photocurrent is in rather good agreement with the value 1.61 eV obtained from temperature dependence of the dark conductivity. The Lux-Ampere characteristics can be described by I ∝ L α but changes in α with illumination intensity and temperature show that at least two different local centers are involved in the carrier recombination mechanism.  相似文献   

12.
PEC studies on the single crystals of the metal-cluster oxide compounds. A2Mo3O8 (A = Zn, Mg, Fe), and polycrystalline LiYMo3O8 are reported. The photoresponse behaviour is attributed to the Mod-d transition. The photopotential, the photocurrent vs applied voltage and the wavelength data indicate thatn-Zn2Mo3O8 is stable and possesses a small and indirect band gap of 1·55 eV and a direct band gap of 1·9 eV. With change in A ions in A2Mo3O8, there is no significant change in the PEC properties. LiYMo3O8 is found to be ofp-type. PEC studies show that excepting for poor electronic conductivity, A2Mo3O8 possesses all the requisitie characteristics of an ideal photoanode for PAE of water for trapping solar energy.  相似文献   

13.
CuIn5Se8 homogeneous crystals of n-type conductivity have been grown. Donor centers activation energy has been estimated. In/n-CuIn5Se8 Schottky barriers have been created and the first spectral dependencies of quantum efficiency of photoconversion of these structures have been derived. The nature of interband optical transitions has been interpreted and the band gap values for direct and indirect transitions in CuIn5Se8 crystals have been determined on the results of analysis of the Schottky barriers photoactive edge absorption. A possibility of utilization of CuIn5Se8 crystals in wide-band photoconverters of the optical radiation has been established.  相似文献   

14.
The photocurrent and optical transmission spectra of thin (As2S3)0.3(As2Se3)0.7 glass films doped with Sn and Pb are reported. The strongest photoresponse is offered by the films doped with 0.010– 0.015 at % Sn or Pb. Low doping levels are shown to have a significant effect on the peak-response wavelength and band gap of the films.  相似文献   

15.
Abstract

Zinc oxide thin films with c axis orientation were grown on Si (100) by radio frequency magnetron sputtering in mixture of argon and oxygen environment using Zn target. These films are treated in hydrogen peroxide (H2O2) solution at room temperature for one hour and two hours. During this study it has been found that post-deposition treatment of ZnO films improves the film quality. Structural, electrical and optical properties have been compared before and after H2O2 treatment by X-ray diffraction analysis, ac conductivity, band gap and refractive index. The full width at half maximum decreases after post-deposition process, which improves the crystal quality. The relief in stress has been observed but films are not fully stress free. The film after treatment becomes highly insulating having resistivity of the order of 1014 Ω cm?1 and can be used for piezoelectric applications. The increase in the band gap and refractive index, near to bulk value, has been observed after post-deposition treatment indicating the increase in grain size and crystal quality.  相似文献   

16.
It is established that the partial substitution of gallium for manganese (3 mol %) in TlGaS2 single crystals leads to a decrease in width of the band gap (from 2.62 to 2.5 eV), broadening of the peak of intrinsic photocurrent, and appearance of a broad band of extrinsic photocurrent over the photon energy range hν = 1.7–2.4 eV. Upon the partial substitution Ga → Mn in TlGaS2, the X-ray sensitivity coefficient increases significantly (by a factor of 24–57) within an irradiation dose of 0.75–78 R/min, and the current-dose characteristics of TlGa0.97Mn0.03S2 have good reproducibility.  相似文献   

17.
We report effect of oxygen vacancies on band gap narrowing, enhancement in electrical conductivity and room temperature ferromagnetism of SnO2 nanoparticles synthesized by simple chemical precipitation approach. As the calcination temperature is elevated from 400 to 800 °C, the average particle size increases from 12.26 to 34.43 nm, with enhanced grain growth and crystalline quality. At low temperatures, these nanoparticles are in a rather oxygen-poor state revealing the presence of many O vacancies and Sn interstitials in SnO2 nanoparticles as in this case Sn+2 is not oxidized completely to Sn+4 and small sized nano particles have more specific surface area, hence defects are more prominent. The oxygen content increases steadily with increasing temperature, with the Sn:O atomic ratio very near to the stoichiometric value of 1:2 at high temperatures suggesting the low density of defects. The optical band gap energies of all SnO2 nanoparticles are in the visible light region, decreasing from 2.89 to 1.35 eV, while room temperature ferromagnetism and electrical conductivity are enhanced with reduced temperatures. The dielectric constant (εr) exhibited dispersion behaviour and the Debye’s relaxation peaks were observed in tanδ. The variation of dielectric properties and ac conductivity revealed that the dispersion is due to Maxwell–Wagner interfacial polarization and hopping of charge carriers between Sn+2/Sn+4. The narrowed band gap energies and enhanced ferromagnetism are mainly attributed to the increase of defects density (e.g., oxygen vacancies). The presence of oxygen vacancies is confirmed by EDX, Raman, PL, XPS, and UV–Vis spectra. The band gap of 1.35 eV is the smallest value for SnO2 reported so far. This rather small band gap, enhanced conductivity and room temperature ferromagnetism demonstrate that SnO2 nanoparticles are very promising in the visible light photo catalysis and optoelectronic devices.  相似文献   

18.
The spectral response of the photocurrent through MnIn2S4 single crystals was measured in the temperature range from 77 to 300 K. A considerable photoresponse was detected in the spectral range from 350 to 900 nm. Slow and fast recombination centers were found in the band gap of MnIn2S4  相似文献   

19.
Mo0.5W0.5Se2 thin films were obtained by using relative simple chemical route at room temperature. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, scanning electron microscope, optical and electrical properties. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction pattern shows that thin films have a hexagonal phase. Optical properties show a direct band gap nature with band gap energy 1.44 eV and having specific electrical conductivity in the order of 10−5 (Ωcm)−1.  相似文献   

20.
Glasses with the composition, (Sm2 O 3) x (ZnO)(40-x)(TeO 2)(60), were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.  相似文献   

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