Electrical Photoconductivity Research Articles

Enhanced Electric Photoconductivity of Modified Epoxy Resin

The basic idea of this study is based on the hypothesis that it is possible to obtain nanostructures by stimulating local chemical reactions. Starting with this hypothesis we assumed that it is possible to disperse some inorganic agent into the epoxy resin and stimulating the mixtures we could get some nano-structures what are changing the basic electric behaviour of the polymer matrix. We dissolved some metallic chlorides in DMF (dimethylformamide) and we mixed together the solution with the epoxy resin (the main component). Applying various external stimuli we get materials showing various properties, different from the epoxy resin properties. The electric photoconductivity is increased (in some cases) but the mechanical properties are damaged due the solvent presence into the polymer matrix.

Optical and photoelectrical properties of low-concentration-Mn-doped CsPbBr3 nanocrystals

Doping of cesium lead bromide (CsPbBr3) perovskite nanocrystals offers effective control of their optical and optoelectrical properties, leading to possibilities of several new applications. Herein, cesium lead bromide perovskite nanocrystals are synthesized with doping of a low concentration of manganese (Mn) into the perovskite lattice using manganese (II) chloride (MnCl2) as a precursor. The shift in X-ray diffraction peaks toward higher angles indicates that manganese as a dopant is present inside the cesium lead bromide lattice. A change in the manganese (II) chloride precursor concentration from 5 to 10 mmol results in an increment in the atomic percentage of manganese from 0.3 to 0.5% in the cesium lead bromide crystal. Doping of a low concentration of manganese (0.3 at.%) into cesium lead bromide results in enhancement of green emission, while doping with a higher concentration of manganese (0.5 at.%) results in blue emission. The band gap of cesium lead bromide nanocrystals increases from 2.31 to 2.53 eV with an increase in the concentration of manganese. The dark and photoelectrical conductivity of cesium lead bromide nanocrystals is improved in the case of doping with a low concentration (0.3 at.%) of manganese. The ratio of photocurrent against dark current is found to be ∼182 in manganese-doped cesium lead bromide crystal film as compared with ∼101 for undoped cesium lead bromide crystal film. Doping with a low concentration of manganese improves the overall electrical and photoelectrical conductivity of cesium lead bromide perovskite nanocrystals.

On the Physical Properties PEDOT:PSS Thin Films

A complete characterization from optical, morphological, electrical, photo-electrical and thermo-electrical point of view was done for PEDOT:PSS thin films and DMSO and EG sensitized PEDOT:PSS films. The studies on the electrical conductivity and electrical photoconductivity allowed the calculation of different relaxation times. The relaxation time of the electrical conductivity is of order of femtosecond and is multiplied by a factor 10 when PEDOT: PSS thin films were deposited on surfaces sensitized with DMSO and EG. Besides, the photoconduction excitation and relaxation times are of order of seconds. An increase in the relaxation photoconduction time by 2 was observed for films deposited on surfaces sensitized with DMSO and by 1.2 for films deposited on surfaces sensitized with EG. The time response of electrical conductivity after exposure to light adds supplementary knowledge for the understanding of the inertial processes, or hysteresis behavior of organic or perovskite solar cells involving PEDOT:PSS films. The electrical conductivity increases with the temperature and the use of DMSO and EG as surfactants lead to higher values of electrical conductivity and Seebeck coefficient. A better stability of the electrical conductivity with the temperature increase, was noticed for films deposited on surfaces sensitized with DMSO.

Three-Dimensional-Coordination Polymer of Zn(II)-Carboxylate: Structural Elucidation, Photoelectrical Conductivity, and Biological Activity.

A newly designed mixed-ligand coordination polymer [Zn4(bdc)4(ppmh)2(H2O)]n (1) (H2bdc = 1,4-benzene dicarboxylic acid, ppmh = N-pyridin-2-yl-N′-pyridin-4-ylmethylene-hydrazine) has been characterized using different physicochemical techniques. The structure has been confirmed by single crystal X-ray diffraction measurements. There are two pyridyl-N and one hydrazino-imine-N donor centers in ppmh, where two pyridyl-Ns bind simultaneously to two Zn(II) to serve as a bridging agent to form a coordination polymer. The 1,4-benzene dicarboxylato (bdc) is ligated via the aromatic dicarboxylato-O to form a one-dimensional (1D) chain. These two 1D chains about Zn(II) constitute a two-dimensional structure, which undergoes noncovalent interactions (C–H···π and π···π) to generate a three-dimensional supramolecular assembly. Electrical conductivity of 1 is higher by 1 order (1.37 × 10–6 S/cm) than that of the free ligand, ppmh (6.2 × 10–7 S/cm). Especially, the responsivity of the compound 1 was 56.21 mA/W, which is 11 times higher than that of the ligand ppmh (5.12 mA/W). The specific detectivity of the compound was 2.17 × 1010 Jones, which is also almost 10 times higher with respect to the specific detectivity of the ligand-based device (4.53 × 109 Jones). The results show that the compound can be valuable for optoelectronic fields. The biological studies suggest that compound 1 is antibacterial as well as a promising anticancer agent (LD50, 42.2 μg/mL against HepG2 cells), while ligands remain silent. Investigation of the mechanism of the cell killing activity of compound 1 accounts the generation of intracellular reactive oxygen species.

Investigation on thermophysical properties of RE6UO12(s) (RE = La, Pr, Nd, Sm)

RE6UO12(s) (RE=La, Pr, Nd, Sm) was synthesized by citrate-nitrate combustion method. The synthesis condition for Pr6UO12(s) was optimized. Nonstoichiometry in these rare earth uranates in argon atmosphere was analysed using various techniques like thermogravimetry (TG), X-ray photo electron spectroscopy (XPS), chemical analysis and electrical conductivity measurements. Thermal expansions of RE6UO12(s) (RE=Pr and Sm) was studied in the temperature range 298–1273K by high temperature X-ray powder diffractometry and compared with that of similar rare earth compounds reported in the literature. Heat capacity of RE6UO12(s) (RE=La, Pr, Nd, Sm) was measured by differential scanning calorimetry in the temperature range 300–870K. Enthalpy, entropy and Gibbs energy functions of these compounds were computed from the measured heat capacity data.

Electron transport and photoelectrical behavior of poly(N-vinylcarbazole)/Poly(3,4-ethylenedioxythiophene) composite honeycomb-patterned films

New type of poly(N-vinylcarbazole) (PVK) polymer nanocomposites were prepared by a solid-state polymerization of N-vinylcarbazole in the presence of different concentration (wt%) of poly(3,4-ethylenedioxythiophene) (PEDOT). The prepared PVK/PEDOT nanocomposites were characterized by using Fourier transform infrared (FTIR) and UV-vis spectra. The transmission electron microscopy (TEM) and X-diffraction studies were performed to understand the surface morphology and nature of the polymer composites. The characterization and morphological studies suggest that there is a conjugation between PVK and PEDOT. Furthermore, the honeycomb-patterned films were obtained by dissolving the PVK/PEDOT nanocomposites into the chloroform solvent under humid conditions. The temperature-dependent DC electrical conductivity and room temperature photo-electrical conductivity of the honeycomb-patterned films were measured. Results showed that the incorporation of PEDOT in PVK polymer has greatly improved the electrical conductivity and photo-electrical behavior of the PVK/PEDOT nanocomposites.

Photo electrical and optical anomaly in ferromagnetic cobalt doped ZnO nanostructures

For the development of novel devices, the correlation of oxygen vacancies and room temperature ferromagnetism in cobalt doped zinc oxide nanostructures synthesized by Co precipitation route reported earlier Zia et al (2014 Phys. Scr. 89 105802) has been further explored on the basis of structural, optical, magnetic and photoelectrical measurements. In the current study, x-ray diffraction data is further exploited for the measurement of d-spacing, c-direction growth for the plane (002) and cell volume. Increased volume of the unit cell is observed with the increase in cobalt content. UV–visible absorption spectroscopy analysis reveals the reduction in optical energy band gap with the increase in cobalt concentration. The saturated and remanence magnetization were found to be increasing with cobalt addition during the magnetic analysis. The photoelectrical conductivity has maximum value for the sample Co (3% mol) and least recovery time as compared to Co (0% mol). The sensing response was found to be decreasing with the addition of cobalt. The anomalies in the photoelectric parameters clearly reflect the presence of photoconductive nature, which may have ramifications for device engineers.

Enhanced photoelectrical conductivity of poly (3-hexylthiophene) by incorporation of ZnS nanoparticles

This paper reports an enhanced photoconduction behaviour of organic (poly 3-hexylthiophene)–inorganic (zinc sulphide) hybrid system. Poly (3-hexylthiophene) (P3HT) and ZnS nanoparticles have been synthesized by chemical route at 0°C and 80°C, respectively. The separately prepared organic–inorganic materials were blended in a nanohybrid system and coated over to ITO electrodes to forms different samples with different concentrations (5–15wt%) of ZnS nanoparticles. The UV–visible spectra of these hybrid materials show an increase in the FWHM with ZnS nanoparticles, attributing to the enhanced optical properties. The photoconduction behaviour of the prepared samples has been investigated through current–voltage (I–V) measurements carried out under dark and light with fixed intensity (∼4.0W/m2) of tungsten lamp. It is observed that photocurrent increases with ZnS concentration. Also, quenching has been observed for the samples having higher concentration of ZnS nanoparticles, in P3HT matrix. The temperature dependence of electrical current in dark and light shows that the decrease in the resistivity with the temperature is more pronounced in the presence of light, indicating a photon activated process.

ZnO–Cellulose Composite for UV Sensing

A novel method to fabricate a composite material made by compressing Zinc Oxide (ZnO) crystals and cellulose fibers is reported. The fabricated material shows electrical photoconductivity changes when exposed to ultraviolet (UV) light. Mixing cellulose fibers with ZnO yields a higher photosensitivity than the one obtained from devices mainly made of ZnO. The structural, electrical, and photosensitivity tests are performed for these mixtures with the goal to determine the mechanisms enhancing their sensitivity as well as finding an optimal ZnO-cellulose composition for the fabrication of sensors. A device made from a mixed 50-50 wt% composition of ZnO and cellulose yields the best sensitivity to UV, suggesting that the enhancement could be because of the higher oxygen permeability of the cellulose matrix facilitating the O2 adsorption-desorption processes on the ZnO surface.

Variability of physical characteristics of electro-sprayed poly(3-hexylthiophene) thin films

Structural and electronic properties of homogeneous poly(3-hexylthiophene) (P3HT) films obtained from the electro-spray method were presented by means of grazing incidence x-ray diffraction, atomic force microscopy, optical absorption, photoelectron spectroscopy, and (photo)electrical conductivity. Starting from different solution concentrations and flow rate conditions, differently assembled thin films were obtained whose physical properties were peculiarly different from those ones obtained by other deposition methods. If properly refined, the method could in principle broaden the spectrum of the existing nano and microscale structures of the P3HT thin films.

Effect of plasma power on properties of a‐SiC:H films deposited by DC magnetron sputtering

AbstractThe effect of plasma discharge power on the properties of a‐SiC:H thin films deposited by DC magnetron sputtering from the use of a liquid source based on hydrocarbon (triméthylphosphine: TMP, (P(CH3)3) are presented. The liquid source based of trimethylphosphine is introduced into the deposit chamber by using hydrogen as carrying gas. The samples were characterized by optical transmission, infrared absorption (FT‐IR) and electrical conductivity measurements. Optical transmission showed that the increase of the plasma discharge power induced a decrease in optical gap energy value accompanied by an increase of refractive index due to a reduction of Si‐H bonds and the carbon film content. Infra‐red absorption measurements clearly evidenced the appearance of additional bands relating to the constituent elements of the TMP (H, C, P). In the same way, a reduction in the phosphorus and carbon contents with the increase of the discharge power is observed. The electrical conductivity measurements have revealed a change of electrical properties of a‐Si:H(P) layers and the doping efficiency with the plasma power. They also clearly evidenced carbon incorporation in a‐Si:H matrix which limits the phosphorus doping effectiveness. The effect of the annealing temperature on the electric photoconductivity of material was also studied. We clearly evidenced that the a‐SiC:H(P) films are photoconductive with an improvement after a thermal annealing in the range of 130–250 °C correlated with an activation of the phosphorus atoms in the a‐Si:H matrix. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoconductivity Measurements of Organic Polymer/Nanostructure Blends

AbstractIn an attempt to produce low cost and high quality polymer/nanoparticle blends for use in hybrid organic/inorganic photovoltaic devices we prepared blends of dihexylsexithiophene and tetragonal barium titanate particles. These polymer nanoparticle blends were deposited as films by spin coating and sublimation. The films were characterised and compared using a wide range of techniques; The electrical photoconductivity analysis of these structures carried out using an HP4140B picoammeter and a solar simulator after aluminium gap cell electrodes had been deposited on the films by sublimation, spectroscopic studies (FTIR and UV-VIS) were carried out to understand the photoconductivity measurements and ellipsometry was used to determine the thickness of the films. The photoconductivity of the spin coated films was the highest reaching 8.5x 10-10A at 20 V, the sublimed films reached ~4 x 10-10A at 40V. This is thought to be due to the thinness of the sublimed films combined with the inhomogeneous distribution of nanoparticles compared with the spin coated film. Sublimed films have been shown by others to be better structured than spin coated films, if this property can be utilized with further optimization of the sublimation process then this technique offers the potential to produce very thin high quality films for use in organic and hybrid photovoltaic devices.

Enhanced photoconductivity and fine response tuning in nanostructured porous silicon microcavities

We used light confinement in optical microcavities to achieve a strong enhancement and a precise wavelength tunability of the electrical photoconductance of nanostructured porous silicon (PS). The devices consist of a periodic array of alternating PS layers, electrochemically etched to have high and low porosities – and therefore distinct dielectric functions. A central layer having a doubled thickness breaks up the symmetry of the one-dimensional photonic structure, producing a resonance in the photonic band gap that is clearly observed in the reflectance spectrum. The devices were transferred to a glass coated with a transparent SnO2 electrode, while an Al contact was evaporated on its back side. The electrical conductance was measured as a function of the photon energy. A strong enhancement of the conductance is obtained in a narrow (17nm FWHM) band peaking at the resonance. We present experimental results of the angular dependence of this photoconductance peak energy, and propose an explanation of the conductivity behaviour supported by calculations of the internal electromagnetic field. These devices are promising candidates for finely tuned photoresistors with potential application as chemical sensors and biosensors.

TiO2및 Ag 스퍼터링-TiO2플라즈마 용사피막의 광전류 및 광분해 특성

Abstract In this study, we investigated photocatalytic ability of plasma sprayed TiO 2 and Ag sputtering TiO 2 (Ag-TiO 2 ) coatings. A sputtering processes were adopted to coat the surface of TiO 2 with Ag(99.99%). Ag was sputtered at 10mA, 450V for 1~11 seconds. TiO 2 and Ag-TiO 2 coatings were heat-treated at 250, 300, 350,400℃ for 0~240seconds. Photoelectrical conductivity was measured by four-point probe, and photodegradation 2-5) was calculated by UV-V is spectrometer. Microstructure observation of TiO 2 and Ag-TiO 2 coatings were investigated by SEM. Crystal structure of TiO 2 and Ag-TiO 2 coatings were investigated by XRD. Qualitative analyses of TiO 2 and Ag-TiO 2 coatings were conducted by EDX. When TiO 2 coatings were heat-treated at 350℃ for 30 sec, photoelectrical conductivity and photodegradation were best. And in XRD analysis result, (101)/(110) relative intensity ratio of TiO 2 (rutile) was comparably changed with photoelectrical conductivity. When Ag-TiO 2 coatings were heat-treated at 350℃ for 30 [sec] after sputtering Ag for 7 sec, Photoelectrical conductivity and photodegradation are best. Surface of coatings in such condition has very small and uniform Ag particles. Key Words : Photoelectrical conductivity, Photodegradation, TiO

Two‐Dimensional SnS2 Nanoplates with Extraordinary High Discharge Capacity for Lithium Ion Batteries

Two-dimensional (2D) layered nanostructures have received increasing interest due to their unique nanoscale phenomena and their potential applications ranging from electronics and energy to catalysis. Recent investigation has revealed that laterally confined layered nanocrystals (LCLN) have remarkably enhanced electrochemical properties compared to their bulk counterparts owing to nanoscale characteristics that include large surface areas, finite lateral sizes, and enhanced open-edge morphologies. Among the variety of layered materials that have been described, tin sulfides are of particular interest because of their unique structural properties. SnS2 has a layered CdI2-type structure, composed of tin atoms sandwiched between two layers of hexagonally disposed closepacked sulfur atoms. The 2D layered characteristics of this substance are revealed in alkali metal intercalation phenomena, and by investigating anisotropy of properties such as electric and photoelectric conductivity. Owing to their large theoretical capacities for battery applications, bulk or micron sized tin-based materials have been extensively studied as possible alternatives for commercially available carbon electrodes. However, the main drawback of this system has been stemming from the large volume changes and accompanying sharp decrease in capacity that occur during electrochemical cycles. Aifantis et al. have reported that active sites with spherical and smaller volume fraction could improve electrochemical properties of anode materials from the view point of fracture mechanics. Other researchers also have reported that nanoscale tin sulfide-based materials would lead to an improvement in the cycling stability of these systems. Especially, layered SnS2 nanoplates with swelling tolerant hosting spaces and enhanced guest accessibility would provide enhanced diffusion for Li ion, and lead to the formation of Li-Sn alloy during the cycle, and improve the

Influence of gas atmosphere and temperature on the conductivity and the photoconductivity of a TiO2single crystal in the surface region

The electrical photoconductivity and conductivity at (and near) the surface of a TiO(2) single crystal (rutile) was studied in a range of temperatures between 300 and 573 K and under different ambient gases (oxygen and nitrogen) by means of impedance spectroscopy. The long times required (many hours) to reach steady state photoconductivity can be explained by the reduction of the material upon illumination. At about 475 K a maximum is observed in the equilibrium photoconductivity and a minimum in the rate constants of the rise and decay after switching on and off, respectively, the light. After switching off the light a fast decay takes place during the first milliseconds followed by a slow exponential decay. The first one is related to recombination through defects, while the latter is due to re-oxidation processes of the material. The results are correlated with measurements of photocatalytic activity.

An explanation of optical phenomena in non-crystalline semiconductors

Abstract Barrier model of a non-crystalline semiconductor is described in this article. The most important optical phenomena, which are typical for this group of materials, are explained on the base of this model. The model assumes that in non-crystalline semiconductors the potential barriers exist, which separate certain microscopic areas from each other, assuming barriers possess a parabolic profile. This conception explains the rise of exponential tails of optical absorption at the end of optical edge as well as electroabsorption, photoelectric conductivity, photoluminescence, and others. Using this model, many electric transport properties of non-crystalline semiconductors can be explained successfully.

Oxygen diffusion in alkyl-substituted titaniumoxo phthalocyanine films

The diffusion coefficients, D, of oxygen in titaniumoxo phthalocyanine (TiOPc) films are determined by following the increase of electric photoconductivity of the films upon oxygen sorption. The diffusion coefficient in as-deposited films of unsubstituted TiOPc is D≈8×10 −16 cm 2 s −1. Introduction of alkyl spacers leads to the increase of D by an order of magnitude. Scanning electron micrographs and extended X-ray absorption fine structure (EXAFS) measurements show that this increase is due to the amorphous structure and the larger distances between the conjugated π-systems in films of substituted Pc’s. As photo-oxidation of the films is a diffusion controlled process, its quantum yield, φ p, increases 10-fold upon alkyl-substitution. Annealing the films leads to microcrystalline films with a closer alignment of the π-conjugated systems, as demonstrated by the changes in the UV-Vis absorption spectra. Consequently, D decreases by approximately an order of magnitude.

The Effect of TAI Addition on the Ionic Conductivity and Photoelectron Lifetime of Silver Halide Emulsion Microcrystals

The effect of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindenee (TAI) addition on the electric properties (photoelectric lifetime and ion conductivity) of tabular silver halide microcrystals and their sensito-metric properly has been studied. The result shows that the addition of TAI decreases the ionic conductivity of the tabular silver halide microcrystals and prolongs their photoelectron lifetimes, thus to some extent promoting the sensitivity enhancement of the emulsion.

Comparison of the Photoelectronic and Photocatalytic Activities of Various Anatase and Rutile Forms of Titania in Pure Liquid Organic Phases and in Aqueous Solutions

Various titania samples of industrial origin (Degussa and Tioxide) have been characterized by electrical photoconductance measurements and tested as photocatalysts in various liquid media (either pure organic liquids or aqueous solutions) as a function of their structure (anatase versus rutile). Anatase was constantly found more active than rutile, whatever the reaction chosen (mild oxidation of pure cyclohexane and 2-propanol; total degradation of phenol and nitrophenol isomers in water). In identical conditions, Degussa was found more active, but the intrinsic activity, expressed in moles converted per hour and per square meter of active surface, was found slightly higher for anatase Tioxide. The higher activity of anatase with respect to that of rutile could be explained by the interpretation of the photoconductance measurements, which evidence the higher aptitude of anatase (i) to photoadsorb oxygen, in O2- and O- forms; (ii) to photodesorb it; and (iii) to have a lower relative electron−hole recombin...