Increase In Current Efficiency Research Articles

Effects of DIO on the charge recombination behaviors of PTB7:PC71BM photovoltaics

Abstract The influence of the solvent additive 1, 8-diiodooctane (DIO) on the charge carrier recombination behaviours of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b0] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediy1]] (PTB7): phenyl-[6, 6]-C71-butyric acid methyl ester(PC71BM) organic photovoltaics (OPVs) was investigated. The measurement of transient photocurrent (TPC) implies that the devices processed with 3% DIO have less charge carrier recombination loss than the devices without DIO. The photo-induced charge extraction by linearly increasing voltage (photo-CELIV) technique shows that the device with DIO has less charge carrier trap population and thus the bimolecular recombination can be reduced. The modified Onsager–Braun model with bimolecular recombination rate γ b i , calculated from the photo-CELIV, indicated that by adding DIO, the binding energy of the charge-transfer exciton at the interface of PTB7 and PC71BM reduced, thus the geminate recombination loss decreased. Atomic Force Microscope (AFM) images show that DIO can optimize the morphology of the active layer, which is beneficial to the exciton dissociation and the reduction of the charge carriers trapping. The reduction of the charge carrier recombination including geminate recombination and non-geminate recombination lead to the large increase of current density (JSC), fill factor (FF), and power conversion efficiency (PCE) of PTB7:PC71BM OPVs.

Facile Electrolytic Synthesis of ϒ- Manganese Dioxide From Manganese Sulphate Solutions In The Presence of Betaine

Manganese dioxides (MnO2), which are of great use in industrial sector, now draw huge attention for purposes pertaining to storage of energy and fuel cells. Effect of different concentrations of dopant on the synthesis, morphology and electrochemical performances of MnO2 has been studied. In this context, betaine as impurity or dopant in the electrolytic solution was observed to improved the cell voltage, current efficiency and energy consumption during deposition of electrolytic manganese dioxide (EMD). It was observed that better electrodeposition performance was achieved when concentration of betaine was varied from 0 to 50 ppm. There was a sharp increase in current efficiency from 92.5 to 96 % and low cell voltage from 2.458 to 2.446 V and less energy consumption from 1.639 to 1.518 KWhKg-1 Finally, the results of the characterization of MnO2 obtained shows to be nano-size particles, which ensures high surface area of the materials and also one of the important requirement for high discharge capacity batteries.

Effect of jet flow between electrodes on power consumption and the apparent density of electrolytic copper powders

Electrolysis is one of the main methods for producing copper powder, but has the disadvantage of high power consumption. This paper describes an experimental study of a process for electrolytic production of copper powder in which a jet flow of fresh electrolyte is introduced between anode–cathode pairs. The effects of electrolyte inlet mode and circulation rate on the direct current (DC) power consumption and on the morphology and apparent density of the copper powder produced are investigated. The results show that in the conventional bottom-inlet/top-outlet mode, the electrolyte circulation rate has little influence on DC power consumption. In contrast, when a jet flow is used, an increase in electrolyte circulation rate leads to an increase in current efficiency and a decrease in cell voltage, resulting in a significant reduction in DC power consumption, which drops by as much as 37%. In addition, as a result of agitation by the jet flow, the copper powder deposited at the cathode becomes denser, the powder particles become coarser and less dendritic on the microscale, and their apparent density increases from 0.33 g cm−3 to 1.90 g cm−3.

Overcoming the trade-off between exciton dissociation and charge recombination in organic photovoltaic cells

The electron donor-acceptor (D-A) interface is an essential component for realizing efficient exciton dissociation and charge generation in organic photovoltaic cells (OPVs). It can also however enable rapid charge recombination due to the close spatial proximity of electrons and holes. To frustrate recombination losses, attempts have been made to separate charge carriers by introducing an insulating blocking interlayer at the D-A interface. It is challenging to realize increased efficiency using this approach as the relative similarity of interlayer optical and transport energy gaps may also frustrate exciton harvesting and charge generation. To overcome this trade-off, the interlayer must block charge carriers while continuing to permit exciton migration to the dissociating interface. In this work, we demonstrate this configuration in archetypical copper phthalocyanine (CuPc)-C60 planar OPVs containing a rubrene interlayer to frustrate charge recombination. Critically, the similarity in triplet exciton energy levels between rubrene and CuPc allows the interlayer to be permeable to excitons. Devices containing an interlayer show a reduction in the charge transfer state binding energy and non-geminate recombination rate with increasing interlayer thickness. For thin interlayers, geminate recombination is also suppressed. Thus, devices containing an exciton permeable interlayer show a simultaneous increase in open-circuit voltage, short-circuit current, and power efficiency.

Vapor textured aluminum-doped zinc oxide on cellophane paper for flexible thin film solar cells

Paper-based flexible thin film solar cells are promising power sources for the emerging portable and wearable electronics, for which high conversion efficiency and flexibility are demanded. Herein, flexible thin film silicon solar cells using textured aluminum-doped zinc oxide (AZO) for light scattering, and ultrathin silver electrodes combined with cellophane paper substrates, were demonstrated. A universal route to form textured AZO thin film by chemical etching with hydrochloric acid vapor was proposed. The AZO layers textured in this way exhibited similar light scattering properties as compared with state-of-the-art AZO thin films. Applying textured AZO to solar cells on cellophane paper substrates resulted in current density and conversion efficiency increase from 8.7 to 9.5 mA/cm2 and from 4.1% to 5.7%, respectively. Thin film solar cells on cellophane exhibited excellent mechanical flexibility, which maintained 90% of their initial efficiency after bending at a radius of 1 mm for 50 cycles.

The enhanced effect of oxalic acid on the electroreduction of Cr(VI) via formation of intermediate Cr(VI)-oxalate complex

ABSTRACTIn this study, the enhanced effect of oxalic acid (Ox) on Cr(VI) electroreduction was evaluated. It was found that for Cr(VI)-contaminated solution ([Cr(VI)]0 = 1.0 mM, pH = 3.0), addition of 5.0 mM Ox can significantly increase Cr(VI) reduction from 0.36 to 1.0 mM within 90 min electrolysis reaction, accompanying with the increase of current efficiency from 19% to 53%. Increasing initial Ox concentration (0–10 mM) and electric current (10–40 mA) facilitated Cr(VI) reduction, whereas it was inhibited with decreasing solution pH value (2.0–3.5) and elevating Cr(VI) concentration (0.1–2.0 mM), respectively. Results show that reactive electron was the primary reductant for the heterogeneous reduction of Cr(VI) on the cathode. In addition, Ox can also serve as an electron donor for the homogeneous reduction of Cr(VI). During this process, the formation of Cr(VI)-oxalate complex is indispensable for the enhanced Cr(VI) reduction. The coordination of Ox with Cr(VI) did not only make the structure of Cr(VI) more distorted but also improved the reactivity of Cr(VI) in Cr(VI)-oxalate complex toward reduction reaction. In general, this study provides an energy-efficient and environmentally benign strategy for the treatment of Ox and Cr(VI) co-contaminated wastewater.

Preparation and Thickness Optimization of TiO2/Nb2O5 Photoanode for Dye Sensitized Solar Cells

In recent years, dye-sensitized solar cells (DSSCs) have received much attention as an alternative to silicon-based solar cells due to their various advantages. It is one of the possible options for large-scale roll-to-roll production of photovoltaic cells, on flexible plastic or glass substrates. Nonetheless, due to technical constraints, the maximum efficiency is only half the efficiency of conventional solar cells. Therefore improving the efficiency of DSSC technology is critical for widespread adoption. This work will attempt to summarize the influence of adding mesoporous Nb2O5 nanoparticle in different percentage of weight to TiO2 photoanode. Prepared TiO2/Nb2O5 nanocomposites are characterized using UV-Vis absorption spectroscopy, XRD and FESEM. DSSCs are fabricated and studied for their photovoltaic performance under the illumination of simulated sunlight of 100mWcm-2. Adding Nb2O5 nanoparticles has resulted in an increase of short-circuit current density (Jsc) and efficiency (η) significantly. Also, an attempt has been made to optimize the film thickness by studying efficiency as a function of film thickness. The cell with 24μm thick electrode emerges as an optimized cell with remarkable performance.

Influence of electrodeposition parameters on the characteristics of Mn–Co coatings on Crofer 22 APU ferritic stainless steel

Manganese–cobalt coatings are promising candidates for solid oxide fuel cell (SOFC) interconnection applications because of their high conductivity and good oxidation resistance. In the present study, manganese and cobalt are electrodeposited on Crofer 22 APU ferritic stainless steel. The effects of current density, pH, sodium gluconate \((\hbox {NaC}_{6}\hbox {H}_{11}\hbox {O}_{7})\) concentration, cobalt sulphate concentration \((\hbox {CoSO}_{4}{\cdot }7\hbox {H}_{2}\hbox {O})\) and deposition duration on the microstructure and cathodic efficiency are characterized by means of scanning electron microscopy, weight gain measurements and energy-dispersive X-ray spectrometry, respectively. Results show that increases in current density and deposition duration lead to decrease in current efficiency and deposition rate. Increasing the pH to 2.5 causes an initial rise of current efficiency and deposition rate, followed by subsequent decline. In addition, the increases in sodium gluconate and cobalt sulphate concentrations in the electrolyte solution result in an increase in current efficiency and deposition rate. Moreover, the results demonstrate that the variations in the current density, pH, sodium gluconate (\(\hbox {NaC}_{6}\hbox {H}_{11}\hbox {O}_{7}\)) concentration, cobalt sulphate concentration (\(\hbox {CoSO}_{4}{\cdot }7\hbox {H}_{2}\hbox {O}\)) and duration have a significant effect on grain size, uniformity and the adherence of the coating.

Study of injection and transport properties of metal/organic interface using HAT-CN molecules as hole injection layer

1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) molecule have been studied as hole injection layer for application in organic semiconductor based devices with potential to modify the electronic properties of electrodes due to its strong electron-withdrawing property. Thermally stable hole transport material 2, 7-bis [N, N-bis (4-methoxy-phenyl) amino]-9, 9-spirobifluorene (MeO-Spiro-TPD) has been used to fabricate hole only devices. To make the injection efficient at metal/organic interface and to reduce the driving voltage of the organic devices, the interface has been modified with a thin layer of highly electron accepting HAT-CN material. Modified interface has been investigated at a different range of thicknesses of HAT-CN. This interface modification resulted in the switching of injection limited transport to space charge limited conduction mechanism with the introduction of HAT-CN layer at metal/organic interfaces. The hole injection property has been found to increase with an increase in HAT-CN thickness. When these modified substrates were used as a hole injecting contacts in organic light emitting diodes (OLEDs), they have shown an increase in current density and device efficiency.

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm−3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., “green rust”, are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.Graphical

High-efficiency thin film ZnMgO/ZnO solar cell simulation approach: Temperature dependency, BSF and efficient small signal analysis

Small signal analysis for Al/ZnO/c-Si/Ag heterojunction solar cell structure is investigated in this simulation work. Effect of signal frequency, device temperature and junction interface defect state density on the junction diffusion capacitance and device conductance are thoroughly examined. Built in potential measurement highlights variation from 0.8 to 2.1 eV for the range100 Hz to 8 MHz which showing a good agreement with the practical value. Low temperature (10–100 K) conductance measurement at 2 V biasing results a localised Fermi level state density 9.54 × 1040 cm−3eV−1and evidences variable range hopping conduction. Excellent improvement of short circuit current density and efficiency is observed using MgxZn1-xO window layer. The increase in short circuit current density and efficiency due to the use of the window layer are 31.85 mA cm−2 and 19.17% respectively. For all the study illumination of 400 nm monochromatic light with photon flux 2.8 × 1017 cm−2s−1 and spectral width 10 nm are applied. Uses of 400 nm light is due to study of temperature dependency on open circuit voltage of solar cell. Using 1000 wt/m2 the efficiency of solar cell is enhanced from 19.88% to 23.15%.

Efficient charge generation layer for tandem OLEDs: Bi-layered MoO3/ZnO-based oxide semiconductor

A novel oxide charge generation layer (CGL) with optical and electrical advantages for tandem organic light-emitting diodes (OLEDs) is proposed. The CGL comprises amorphous Zn-Si-O (a-ZSO) and MoO3-x. Although a-ZSO has a very small work function of 3.4 eV, it forms Ohmic contact with MoO3-x with a high work function of 6.6 eV. It is discovered that the interface state appears between a-ZSO and MoO3-x, which contributes to the formation of quasi-Ohmic contact between the two oxides with dramatically different work functions. High performance of electron and hole injection/transport is achieved in tandem OLEDs with a very small voltage drop of 0.4 V at 100 mA/cm2 with a twofold increase in current efficiency. This new CGL provides distinct advantages over conventional organic CGL materials with respect to processing simplicity, cost, and chemical stability.

Uticaj gustine struje i sastava rastvora na iskorišćenje struje elektrohemijske redukcije benzaldehida

This research deals with the effect of current density and benzaldehyde and ethanol concentrations on current efficiency for benzaldehyde reduction at the cathodes: a)-Raney-Ni; b)-a titanium substrate having an electrochemically deposited Ni92Mo8 alloy coating; c)-a titanium substrate having a Ni93Mo7 alloy coating produced by the plasma spraying process; d)-a cathode made from pressed electrogenerated Ni92.8Mo7.2 powder and e)-a zinc amalgam cathode Zn(Hg). Current efficiency increases with benzaldehyde concentration in the solution increasing from 0.4 mol dm-3 to 1.2 mol dm-3. The increase in current efficiency is due to the increased rate of the reaction of adsorbed benzol intermediates with water molecules. The increase in current density leads to a decrease in the cathodic current efficiency. The decrease is caused by the small effect of the cathodic over potential on the rate of the chemical reaction of benzol intermediates with water. As ethanol content in the solution increases, the cathodic current efficiency decreases.

Polymer-based protein engineering grown ferrocene-containing redox polymers improve current generation in an enzymatic biofuel cell

Enzymatic biofuel cells (EBFCs) are capable of generating electricity from physiologically present fuels making them promising power sources for the future of implantable devices. The potential application of such systems is limited, however, by inefficient current generation. Polymer-based protein engineering (PBPE) offers a unique method to tailor enzyme function through tunable modification of the enzyme surface with functional polymers. In this study, we report on the modification of glucose oxidase (GOX) with ferrocene-containing redox polymers to increase current generation efficiency in an enzyme-modified anode. Poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide) (pFcAc) was grown from covalently attached, water-soluble initiator molecules on the surface of GOX in a “grafting-from” approach using atom transfer radical polymerization (ATRP). The covalently-coupled ferrocene-containing polymers on the enzyme surface promoted the effective “wiring” of the GOX active site to an external electrode. The resulting GOX-pFcAc conjugates generated over an order of magnitude increase in current generation efficiency and a 4-fold increase in maximum EBFC power density (≈1.7µWcm−2) with similar open circuit voltage (0.27V) compared to native GOX when physically adsorbed onto paddle-shaped electrodes made up of electrospun polyacrylonitrile fibers coated with gold nanoparticles and multi-wall carbon nanotubes. The formation of electroactive enzyme-redox polymer conjugates using PBPE represents a powerful new tool for the improvement of mediated enzyme-based bioelectronics without the need for free redox mediators or anode/cathode compartmentalization.

Atmospheric spatial atomic layer deposition of Zn(O,S) buffer layer for Cu(In,Ga)Se2 solar cells

Zinc oxysulfide has been grown by spatial atomic layer deposition (S-ALD) and successfully applied as buffer layer in Cu(In, Ga)Se2 (CIGS) solar cells. S-ALD combines high deposition rates (up to nm/s) with the advantages of conventional ALD, i.e. excellent control of film composition and superior uniformity over large-area and even non-flat substrates. Diethylzinc, water and hydrogen sulfite (H2S) have been used as zinc, oxygen and sulfur precursor, respectively. The S/(S+O) ratio in the film is accurately controlled by exposing the substrate simultaneously to both H2O and H2S precursors, which are pre-mixed and co-injected in the same deposition zone. The optoelectronic and morphological properties of Zn(O,S) are characterized as a function of the S/(S+O) ratio. Zn(O,S) buffer layers with different values of S/(S+O) ratio are applied in CIGS solar cells. An optimum value of S/(S+O) ratio of about 0.4 is found for which both the short circuit current density (Jsc=34.2mA/cm2) and cell efficiency (η=15.9%) increase, as compared to reference cells with CdS buffer layer (Jsc=32.1mA/cm2, η=15.5%).

Ultrathin buffer layer at organic/organic interface for managing the recombination profile in organic light‐emitting diodes: Metal versus dielectric buffer

ABSTRACTWe report on the utilization of an ultrathin buffer layer at the organic/organic (O/O) interface to enhance device efficiency in organic light‐emitting diodes. Two different kinds of buffer layers are examined: metal and dielectric. It is shown that employment of an ultrathin Ag layer with a thickness of 1–2 nm enhances the device performance, while a MgF2 dielectric buffer cannot affect the device properties considerably. In particular, the turn‐on voltage of the device with an appropriate buffer layer is reduced about 3 V, its current efficiency increases by a factor of more than three, and the power efficiency increases by a factor of more than five in comparison to the control device when a Ag buffer layer is introduced at the O/O interface. By employment of the buffer layer at the interface, an accumulation of current carriers appears within the device that redistribute the recombination profile toward the interior part of the emissive layer. Also, morphological examinations reveal that distinguishable phase segregation occurs in the blend of the hole‐transport layer. In particular, the polymer component remains at the surface and facilitates the hole transport into the successive layers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43894.

Enhanced performances for top-emitting white organic light-emitting diodes by utilizing green phosphor as energy transfer medium

In top-emitting white organic light-emitting diodes (TWOLEDs), the device performances attribute to the several important factors, such as exciton profile, energy transfer, and microcavity effect. In this paper, a TWOLED containing a heterojunction blue emission layer (EML) and a red EML is reported. A host material with high triplet energy level is employed for the adjacent blue and red EML, while the inefficient red emission reduces the emission efficiency of the TWOLED. In order to enhance the red emission efficiency, mixed-host and co-doping technologies are used in the red EML. By mixing the hole transporting and electron transporting host materials, the exciton recombination zone extends to the red EML to increase the red emission intensity and reduce the efficiency roll-off. And by co-doping a green phosphor into the red EML as the energy transfer medium, the energy transfer rate is enhanced, and then the current efficiency increases. Besides, both the mixed-host and co-doping change the carrier transport and the exciton recombination zone, which further affects the microcavity resonance in the devices. Due to the enhancement on the red emission intensity and the shift of resonant wavelength, the chromaticity of the TWOLED is improved.

All-solution-processed multilayer polymer/dendrimer light emitting diodes

A fully solution-processed deep-blue emitting organic light emitting diode (OLED) based on a highly efficient fluorescent dendritic material with a pyrene core, a phenylene shell and triphenylamine surface groups coupled with polymeric hole (HTL) and electron (ETL) transport layers is demonstrated. Each layer formed smooth and pinhole-free films as demonstrated by Atomic Force Microscopy (AFM) as well as by X-ray Photoelectron Spectroscopy (XPS). Furthermore, detailed Ultraviolet Photoelectron Spectroscopy (UPS) surveys revealed a beneficial energy level alignment and hence improved charge carrier confinement. The resulting triple-layer device saw a 7.7-fold increase in current efficiency compared to a single-layer device while maintaining a deep-blue emission color characterized by the CIE1931 coordinates of x = 0.153 and y = 0.155.

Gains and Losses in PbS Quantum Dot Solar Cells with Submicron Periodic Grating Structures

Corrugated structures are integral to many types of photoelectronic devices, used essentially for the manipulation of optical energy inputs. Here, we have investigated the gains and losses incurred by this microscale geometrical change. We have employed nanostructured electrode gratings of 600 nm pitch in PbS colloidal quantum dot (PbS-CQD) solar cells and investigated their effect on photovoltaic properties. Solar cells employing grating structure achieved a 32% and 20% increase in short-circuit current density (Jsc) and power conversion efficiency, respectively, compared to nonstructured reference cells. The observed photocurrent increase of the structured devices mainly stems from the enhancement of photon absorption due to the trapping of optical energy by the grating structures. This optical absorption enhancement was particularly high in the near-infrared portion of the sun spectrum where PbS-based solar cells commonly present poor absorption. We have interestingly observed that the open-circuit vol...

Efficiency Enhancement of Organic Light-Emitting Diodes on Flexible Substrate With Patterned Inverted Conical Structure

The total internal reflection effect in conventional electroluminescent devices causes a large amount of light energy to be trapped in devices and induces heat energy that adversely affects the performance of the device. To enhance the light outcoupling efficiency without sacrificing the electrical properties, a patterned inverted conical (PIC) structure fabricated by a focused femtosecond laser on a flexible substrate was demonstrated. Compared with the conventional flexible organic light-emitting diode (OLED), the OLED with the PIC structure exhibited a current efficiency increase of a factor of 2.6 with no emission spectrum altered. In addition, the flexible OLED with PIC substrate can avoid the mirror reflection effect under the strong ambient light for a better visual experience. This highly effective method is compatible with the current device fabrication process and is applicable for full-color OLED display and lighting.