Electrical Conductivity Of Films Research Articles

Ionic Conductivity and Structure of Chitosan Films Modified with Lactic Acid-Choline Chloride NADES.

The natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and lactic acid (LA) was used for the preparation of chitosan (CS) films by the solution casting method. The content of NADES in films was from 0 to 82 wt%. The impact of NADES on the morphology and crystalline structure of films was investigated using scanning electron microscopy as well as wide-angle and small-angle X-ray scattering. The experimental results allow to propose CS chains swelling in NADES. FTIR spectroscopy confirms the interactions between CS and NADES components via the formation of hydrogen and ion bonds. The thermal properties of the composite films were studied by simultaneous thermogravimetric and differential thermal analysis. Thermomechanical analysis demonstrated appearance of two transitions at temperatures between −23 and −5 °C and 54–102 °C depending on NADES content. It was found that electrical conductivity of film with 82 wt% of NADES reaches 1.7 mS/cm. The influence of the composition and structure of films on the charge carriers concentration and their mobility is discussed.

Electrical property modified hole transport layer (PEDOT:PSS) enhance the efficiency of perovskite solar cells: Hybrid co-solvent post-treatment

Abstract Poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) layer as a hole transport layer (HTL) plays a key role in efficient hole extraction and transportation of the inverted planar perovskite solar cells (PSCs). However, the insulating nature of PSS lead to lower electrical property of the PEDOT:PSS film, which impedes transferring hole and results in a low photocurrent of the PSCs. In this work, dimethylformamide (DMF), methanol and their mixture solvents (co-solvent) were employed to treat the PEOT:PSS thin film after deposition with different methods to enhance the film's electrical conductivity. Electrical conductivity of the PEDOT:PSS films was increased from 10−3 S cm−1 to ~102 S cm−1 after the co-solvents treatment. Using the highest conductivity co-solvent treated PEDOT:PSS thin film as the HTL in a perovskite solar cell, the power conversion efficiency (PCE) of the device has been measured improved by 17.5% as compared with that of the control device with the untreated PEDOT:PSS film as the HTL. This result shows that the hybrid co-solvent post-treatment is a simple and feasible way to modified the electrical properties of the PEDOT:PSS film as the HTL for high efficient PSCs and other thin film electronic and optoelectronic devices.

The microstructure evolution during MoS2 films growth and its influence on the MoS2 optical-electrical properties in MoS2/p-Si heterojunction solar cells

Abstract The microstructure of MoS2 films is crucial important for its photoelectrical properties, which has significant impact on its application in the field of photovoltaic devices. In this paper, a set of MoS2 thin films with varied thickness was prepared by magnetron sputtering. The influence of the MoS2 microstructure on its optical and electrical properties and, especially, the MoS2/p-Si solar cells photovoltaic performance was investigated in terms of thin films growth. The results reveal that, as the thickness increases, the microstructure of the MoS2 films evolves from amorphous to microcrystalline with the in-plane E2g1 and out-of-plane A1g Raman modes enhancing and the parallel (002) growth orientation increasing. The films electrical conductivity significantly improves owing to the enhanced MoS2 crystallinity. When the thickness is 10 nm, the small ordered MoS2 crystal clusters gradient distribute from the surface to the bulk in the films, contributing to the stress release in the amorphous precursor. Simultaneously, the optical band gap of the MoS2 films shows a maximum of 1.3 eV, due to the less band tail states in the films at the initial phase transition. The optimized optical-electrical properties of the MoS2 films lead to the reducing defects recombination and the enhanced carrier transportation at MoS2/p-Si interface, which promotes the rectification behavior of the pn-junction up to 102. Besides, the significant improvement of the photo-response in MoS2/p-Si heterojunction is obtained, especially in short wavelength range. Correspondingly, the photovoltaic characteristics (Voc, Jsc and FF) of the MoS2/p-Si solar cells increase, and thus an enhancement of the cells conversion efficiency is achieved with 10-nm MoS2 layer.

Improvement of electrical conductivity of PEMA film by incorporating EMITFSI and carbon based nanofiller

Abstract The electrical conductivity of dual inclusion of 1-ethyl-3-methyl imidazolium bis(trifluorosulfonyl) imide ionic liquid and three allotropes of carbon based nanofillers (multiwalled carbon nanotube, graphene and graphite) in poly (ethyl methacrylate) films with thickness ranging from 100 to 250 μm has been investigated in the temperature range of 300–380 K. It is found that the electrical conductivity of film with 0.5 wt % multiwalled carbon nanotube has the highest ambient electrical conductivity of 4.9 × 10−6 Scm−1 which is five order of magnitude higher than pure poly (ethyl methacrylate) film. Moreover, the stability of the highest electrical conductivity is also found to be significantly improved for a longer period. From the investigated physicochemical properties, these improvements are likely can be explained by the aggregation of multiwalled carbon nanotubes, the increase in electronic transport and the reduction in glass transition temperature which likely effect its ionic mobility. Consequently, these enhancements may lead to a promising improvement of its electrical properties for a stable near room temperature application.

Electrical Conductivity of Films with Negative Dielectric Permittivity

The electrical conductivity of films from spherical nanoparticles of metal oxides Al2O3 and NiO, whose surface is saturated with hydrogen atoms, is studied. It is found that under the action of an electric field the films pass into a stable state of polarization. In this unchanged state at a current J ≥ 0, the differential electrical resistance of the films is zero. It is established that the static dielectric constant $$\varepsilon (0,\bar {k})$$ of finely dispersed dielectrics Al2O3, NiO, and KMnO4 saturated with hydrogen has a negative value. At the same time, regardless of temperature (T = 295–500 K), in the case of a constant or sinusoidal current, the ohmic resistance of a powder is zero if it simultaneously satisfies the condition e(0, $$\bar {k}$$) < 0. This effect is a consequence of the negative value of the free energy of a polarized powder.

Electroconductive starch/multi-walled carbon nanotube films plasticized by 1-ethyl-3-methylimidazolium acetate

Starch/multi-walled carbon nanotube (MWCNT) films were prepared by casting using an ionic liquid (1-ethyl-3-methylimidazolium acetate, [emim+][Ac−]) as plasticizer for the first time. The effect of the MWCNT content (0.25–5 wt.%, with respect to the sum of starch and plasticizer mass) on thermal, mechanical and electroconductive behavior of the films was studied. Films containing 0.5 wt.% MWCNT showed increases of 327 % in maximum tensile strength, 2484 % in Young’s modulus and 82 % in elongation at break. The significant improvements are explained by the good MWCNT dispersion in the matrix and by the effect of [emim+][Ac−] as an efficient plasticizer, which leads to higher extensibility. The MWCNT/[emim+][Ac−] combination have a synergistic effect on film electrical conductivity, increasing a 130% (3 wt.% MWCNT). These films, easily prepared by a “green” process, have potential applications in the packaging industry but also in the field of lithium batteries, fuel cells and dye-sensitized solar cells.

Assembly of carbon nanodots in graphene-based composite for flexible electro-thermal heater with ultrahigh efficiency

A high-efficiency electro-thermal heater requires simultaneously high electrical and thermal conductivities to generate and dissipate Joule heat efficiently. A low input voltage is essential to ensure the heater’s safe applications. However, the low voltage generally leads to low saturated temperature and heating rate and hence a low thermal efficiency. How to reduce the input voltage while maintaining a high electro-thermal efficiency is still a challenge. Herein, a highly electrical and thermal conductive film was constructed using a graphene-based composite which has an internal three-dimensional (3D) conductive network. In the 3D framework, cellulose nanocrystalline (CNC) phase with chiral liquid crystal manner presents in the form of aligned helix between the graphene oxide (GO) layers. Carbon nanodots (CDs) are assembled inside the composite as conductive nanofillers. Subsequent annealing and compression results in the formation of the assembled GO-CNC-CDs film. The carbonized CNC nanorods (CNR) with the helical alignment act as in-plane and through-plane connections of neighboring reduced GO (rGO) nanosheets, forming a conductive network in the composite film. The CDs with ultrafast electrons transfer rates provide additional electrons and phonons transport paths for the composite. As a result, the obtained graphene-based composite film (rGO-CNR-CDs) exhibited a high thermal conductivity of 1,978.6 W·m−1·K−1 and electrical conductivity of 2,053.4 S·cm−1, respectively. The composite film showed an outstanding electro-thermal heating efficiency with the saturated temperature of 315 °C and maximum heating rate of 44.9 °C·s−1 at a very low input voltage of 10 V. The freestanding graphene composite film with the delicate nanostructure design has a great potential to be integrated into electro-thermal devices.

Carbon Nanotube and Cellulose Nanocrystal Hybrid Films

The use of cellulose nanocrystals (CNC) in high performance coatings is attractive for micro-scale structures or device fabrication due to the anisotropic geometry, however CNC are insulating materials. Carbon nanotubes (CNT) are also rod-shaped nanomaterials that display high mechanical strength and electrical conductivity. The hydrophobic regions of surface-modified CNC can interact with hydrophobic CNT and aid in association between the two anisotropic nanomaterials. The long-range electrostatic repulsion of CNC plays a role in forming a stable CNT and CNC mixture dispersion in water, which is integral to forming a uniform hybrid film. At concentrations favorable for film formation, the multiwalled nanotubes + CNC mixture dispersion shows cellular network formation, indicating local phase separation, while the single-walled nanotube + CNC mixture dispersion shows schlieren texture, indicating liquid crystal mixture formation. Conductive CNT + CNC hybrid films (5–20 μm thick) were cast on glass microscope slides with and without shear by blade coating. The CNT + CNC hybrid films electrical conductivity increased with increasing CNT loadings and some anisotropy was observed with the sheared hybrid films, although to a lesser extent than what was anticipated. Percolation models were applied to model the hybrid film conductivity and correlate with the hybrid film microstructure.

Compression and reduction of graphene oxide aerogels into flexible, porous and functional graphene films

Graphene (GR) films have been demonstrated as great promising materials in many fields, including battery electrodes, supercapacitors, electronics and functional composites. However, the applications of GR films are limited either by their brittleness, small size, or by their unsatisfactory electrical conductivity. Here, we report an efficient methodology for fabricating large size, flexible and electrical conductive GR films, which mainly involves compression of the graphene oxide (GO) aerogels into porous GO films as well as reduction of GO films into porous GR films via chemical or thermal route. The densities of GR films can be adjusted by controlling the concentration of GO dispersion precursor. The porous GR films exhibit high electrical conductivity up to 5.5 × 103 S m−1 and favourable electromagnetic interference (EMI) shielding effectiveness up to 50 dB in a wide frequency range. The high porosity, excellent electrical conductivity and remarkable EMI shielding effectiveness enable the GR films to be greatly useful in lightweight conductive films, electromagnetic shielding materials and flexible batteries and supercapacitors.

Inverted MAPbI3 Perovskite Solar Cells with Graphdiyne Derivative‐Incorporated Electron Transport Layers Exceeding 20% Efficiency

Chlorine‐substituted graphdiyne (ClGD) is employed into electron transport layers (ETLs) of MAPbI3‐based perovskite solar cells for the first time, forming a high‐quality film with superior film morphology and electrical conductivity as compared with pristine [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) film. Strikingly, a champion power conversion efficiency of 20.34% is achieved, showing a 19% enhancement compared with the counterparts (17.08%). Simultaneously, ClGD‐PCBM‐based devices show suppressed J–V hysteresis. It is experimentally and theoretically demonstrated that the interactions of derivated graphdiyne and PCBM stem from four types of noncovalent bonds, which contribute to the improved device performance. The results suggest that derivated graphdiyne‐based interfacial material is promising for the applications in solar cells and other photoelectric devices.

Tuning optoelectronic properties of SnS thin films by a kinetically controllable low temperature microwave hydrothermal method

In the polycrystalline SnS semiconductor films, the crystallite size and stoichiometry play a central role in dictating their optoelectronic properties. Most strategies to tailoring these parameters require long-time deposition methods and post-deposition thermal annealing at high temperature under inert atmosphere or sulfur vapor. Here, we report a different strategy of tuning optoelectronic properties of SnS films by controlling the kinetical parameters in a microwave-hydrothermal solution method at low temperatures (50–60 °C). The interaction between microwave radiation and the highly polar thioacetamide (TA, sulfur source) enhances local temperature in the reaction solution and permits a rapid formation of orthorhombic SnS crystallites on glass substrates. For as-deposited SnS films, a lineal dependence is observed of the film thickness, crystallite size and electrical conductivity on the TA concentration. In addition, the microstrain, Sn/S ratio and optical band gap of the films decrease with the concentration of TA, leading to the optimal values for stoichiometry and optical properties of SnS films. The ability to synthesize highly crystalline SnS thin films at high growth rates and low temperatures opens up possibilities to the fabrication of SnS-based optoelectronic devices on plastic substrates.

Electroactive and Conformal Coatings of Oxidative Chemical Vapor Deposition Polymers for Oxygen Electroreduction

Polymer from 3,4-ethylenedioxythiophene (EDOT) was synthesized using oxidative chemical vapor deposition (oCVD). To enable the synthesis of PEDOT, two different oxidants, antimony pentachloride (SbCl5) and vanadium oxytrichloride (VOCl3), were utilized. The effect of deposition temperature on the polymer electroactivity and conductivity was evaluated by measuring the overpotential for the oxygen reduction reaction and film electrical conductivity, respectively. PEDOT films with conductivity values of ∼2000 S/cm were deposited in a single step coating and doping process. X-ray photoelectron spectroscopy revealed that the residual metalloid within polymer films, in the case of SbCl5, is contributing to the hole conductivity. The electrocatalytic activity of deposited material in oxygen reduction reaction (ORR) was studied; the results indicate a direct relationship between the conductivity values and the electrocatalytic activities of the deposited films. The unique potential offered by oCVD to coat PEDOT conformally enabled us to apply a coat of electroactive polymers on complex structures of a gas diffusion layer fabric, carbon cloth. Using our approach, we imparted stable electrocatalytic activity to carbon cloth electrodes and fabricated all-organic electrodes for ORR.

Chemical Postdeposition Treatments To Improve the Adhesion of Carbon Nanotube Films on Plastic Substrates.

The robust adhesion of single-walled carbon nanotubes (SWCNTs) to plastic substrates is a key issue toward their use in flexible electronic devices. In this work, semitransparent SWCNT films were prepared by spray-coating on two different plastic substrates, specifically poly(ethylene terephthalate) and poly(vinylidene fluoride). The deposited SWCNT films were treated by dipping in suitable solvents separately, namely, 53% nitric acid (HNO3) and N-methyl pyrrolidone. Direct evidence of SWCNT adhesion to the substrate was obtained by a peel-off test carried out with an adhesive tape. Moreover, these treatments caused enhanced film transparency and electrical conductivity. Electron microscopy images suggested that SWCNTs were embedded in the plastic substrates, forming a thin layer of conductive composite materials. Raman spectroscopy detected a certain level of doping in the SWCNTs after the chemical treatments, which particularly affected metallic nanotubes in the case of the HNO3 treatment. The microscopic adhesion and hardness of the SWCNT films were studied through a nanoscratch test. Overall, the efficiency of selected chemical postdeposition treatments for improving the SWCNT adhesion and the robustness of the resulting SWCNT films are demonstrated on flexible substrates of different chemical compositions.

Electrical conduction mechanism in films of Se80−xTe20Bix (0 ≤ x ≤ 12) glassy alloys

This paper reports the study of DC electrical conductivity of films of Se80−xTe20Bix (0 ≤ x ≤ 12) glasses prepared using physical vapor deposition method. The films were structurally characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM results indicate the formation of nanorods within the films. The electrical conductivity of the samples was studied using Keithley electrometer in the temperature range 303–373 K. The results show that conduction in these samples takes place via thermally assisted tunnelling and variable range hopping of charge carriers corresponding to higher and lower temperature ranges, respectively. Further, it was found that the conductivity increases with increase in Bi concentration in Se–Te system. This has been explained on the basis of chemically ordered network model. It was also found that nanorod formation improves the electrical conductivity of Se–Te–Bi system compared to bulk Se–Te–Bi system.

Temperature Dependence of Electrical Conductivity and Thermoelectric Power of Transparent SWCNT Films Obtained by Aerosol CVD Synthesis

The effect of pressing on temperature dependences of electrical conductivity σ(T) and thermoelectric power (Seebeck effect) S of single‐walled carbon nanotubes (SWCNTs) transparent films on polyester substrate has been studied. σ(T) has been described by the fluctuation‐induced tunneling model (FIT) conductance in the temperature range 20–298 K. At a temperature T &lt; 20 K, three‐dimensional variable range hopping conductivity (VRHC) has been observed. Based on the estimation of current concentration n ≈1020 cm−3 from VRHC dependence, it has been found that metallic SWCNTs have made the main contribution to conductivity at T &lt; 20 K. The value n obtained from S has been similar to the value obtained from VRHC estimation. The energy barrier between SWCNTs has been changed by pressing of films. Such pressing has led to increase in the electrical conductivity of the film by two orders of magnitude at room temperature. The measurement of conductivity in the process of synthesis has allowed us to control the repeatability of results and select samples with the necessary resistance values. Raman and optical spectroscopy, SEM and TEM have been used to determine the structural and geometric characteristics of the SWCNTs.

Room Temperature Bonding of Wafers Using Si and Ge Films with Extremely Low Electrical Conductivity

The technical potential of room temperature bonding of wafers in vacuum using amorphous Si (a-Si) and Ge (a-Ge) films was studied. Transmission electron microscopy images revealed no interface corresponding to the original films surfaces for bonded a–Ge–a–Ge films. Analyses of film structure and the surface free energy at the bonded interface revealed higher bonding potential at the connected a–Ge–a–Ge interface than that of a–Si films. The electrical resistivity of a-Ge films is 0.62 Ωm, which is lower than that of a-Si film (4.7 Ωm), but 7–8 order higher than that of representative material films used for bonding in vacuum. Our results indicate that room temperature bonding using a–Ge films is useful to bond wafers without any marked influence on the electrical properties of devices on wafer surfaces caused by the electrical conductivity of films used for bonding.

XPS analysis of ZnO:Ga films deposited by magnetron sputtering: Substrate bias effect

This work focuses on X-ray photoelectron spectroscopy (XPS) and combined Raman and photoluminescence experiments performed on ∼500 nm thick ZnO:Ga films deposited by magnetron sputtering. The substrate bias voltage applied during the deposition was varied between 0 V (grounded) and −120 V in order to study the effect of Ga-doping on the ZnO wurtzite structure of the films and its electrical properties, when using a fixed doped composition of Ga2O3 (4.5 wt.%) in the ZnO sputtering target. XPS analysis revealed that ZnO dominates in all samples, while the Ga amount is the highest (∼2.9 at.%) for a substrate bias polarization of −60 V, diminishing substantially for either decreasing or increasing substrate polarizations. This increase in Ga concentration is responsible for the enhancement of electronic transport properties, resulting in a minimum electrical resistivity of ∼300 µΩ·cm. Moreover, the atomic layers closer to the surface are deficient in zinc for higher bias, due to the etching effect of Ar+ ions and subsequent Zn re-evaporation. From the Raman experiments, it was observed that the dynamics of the A1 and E1 phonons correlates with the decrease of the electrical resistivity. Photoluminescence studies revealed two broad bands, being one near the ZnO near-band-edge (3.4 eV) and another at higher energies (∼3.6 eV). The band centered at higher energies is more prominent for the case of the more electrically-conductive films, and is ascribed to electron transitions from the conduction band to single ionized oxygen vacancies. The lifetime of the polar-nature longitudinal optical phonons is in the range of 0.1–0.2 ps, which is quite small due to the Fröhlich interactions with gallium dopant atoms and other defects.

Production of self-supported conductive films based on cellulose, polyaniline and silver nanoparticles

Synthetic efforts are being made to produce electrical conductive films based on a combination of cellulose matrix with conducting polymers. Improved mechanical properties and processability of the conducting polymers can be attained by promoting this combination, allowing the production of electrical conductive membranes or sheet of paper-like forms that have many technological uses. Cellulose films containing different amounts of polyaniline combined to silver nanoparticles were prepared in homogenous conditions by the dissolution of microcrystalline cellulose in 1-butyl-3-methylimidazolium chloride ionic liquid, followed by the mixing with dispersion of silver nanoparticles and polyaniline also prepared in an ionic liquid. Films with high electrical conductivities (23–34 S·cm−1) and homogeneous distribution of the constituents were produced. The high conductivity was promoted by the presence of polyaniline in its most conductivity state with the silver nanoparticles affording the electrical contact among these chains creating a conductive network spread throughout the insulating cellulose matrix.

Co-solvents roles in PEDOT:PSS ink-jet inks

The different water soluble ink-jet inks based on conjugated poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were formulated with various organic co-solvents such as diethylene glycol (DEG), triethylene glycol (TRIEG), tetraethylene glycol (Tetra EG), and polyethylene glycol (PEG) to print on the flexible substrate. The effect of adding various organic co-solvents, which show a same trend of molecular weight, dipole moment and boiling point on the formulated inks properties and ink-jet printed films electrical conductivity, morphology and transparency were investigated. The conductivities of the ink-jet printed films were evaluated by four-point probe conductivity measurement. The morphologies of the printed films have been studied using atomic force microscopy and scanning electron microscopy. The size of PEDOT:PSS particles and the printed film morphology altered by addition of different types of co-solvent in the ink-jet ink formulation. The electrical conductivity of the ink-jet printed film increased by raising the molecular weight, boiling point and dipole moment of used co-solvent in ink-jet ink formulation.

Ellipsometry-based conductivity extraction in case of phosphorus doped polysilicon

In this work, we investigated a new method for thin films electrical conductivity extraction based on spectroscopic ellipsometry. This has been enabled through the correlation between the films conductivity and their ellipsometric properties. Indeed, it has been demonstrated that numerous ellipsometric fitting-based approaches can provide, in an indirect way, the electrical characteristics of thin films. The study was focused on electrical conductivity, but doping level or carriers’ mobility can also be extrapolated from ellipsometric measurements. Among various possibilities leading to electrical properties extraction, we can cite the extremal values of Ψ and Δ ellipsometric angles, their associated wavelengths, the mean square error and the maximal and minimal reflectivities ratio. Otherwise, the correlation between extrinsic conductivity and ellipsometric parameters evolution has been confirmed in case of low doping levels with particular behavior after annealing. This contactless method has been successfully applied to polycrystalline silicon films deposited on oxidized, p-type monocrystalline substrates, by low pressure chemical vapor deposition technique, and lightly or heavily phosphorus doped by diffusion. The feasibility of the method has been proven in this case, but also in other cases like implanted polysilicon layers or silicon-on-insulator (not included here).