Absorption Current Measurements Research Articles

Vitamin C for Photo-Stable Non-fullerene-acceptor-Based Organic Solar Cells.

The recent advent of the new class of organic molecules, the so-called non-fullerene acceptors, has resulted in skyrocketing power conversion efficiencies of organic solar cells. However, rapid degradation occurs under illumination, particularly when photocatalytic metal oxide electron transport layers are used in these devices. We introduced vitamin C (ascorbic acid) into the organic solar cells as a photostabilizer and systematically studied its photostabilizing effect on inverted PBDB-T:IT-4F devices. The presence of vitamin C as an antioxidant layer between the ZnO electron transport layer and the photoactive layer strongly suppressed the photocatalytic effect of ZnO that induces NFA photodegradation. Upon 96 h of exposure to AM 1.5G 1 Sun irradiation, the reference devices lost 64% of their initial efficiency, while those containing vitamin C lost only 38%. The UV-visible absorption, impedance spectroscopy, and light-dependent voltage and current measurements reveal that vitamin C reduces the photobleaching of NFA molecules and suppresses the charge recombination. This simple approach using a low-cost, naturally occurring antioxidant, provides an efficient strategy for improving photostability of organic semiconductor-based devices.

Inverted planar heterojunction perovskite solar cells with high ultraviolet stability

Long-term stability remains a challenge for commercializing metal halide perovskites in photovoltaic (PV) applications. Ultraviolet-induced degradation (UV-ID) has been considered as one of the key stability issues for crystalline silicon PVs. However, limited studies have been performed on the long-term UV-ID of perovskite PVs, and none has been found related to operational stability under UV stressing. Here, we focus on UV-ID of inverted perovskite solar cells that comprise nickel oxide (NiO) as the hole transporting layer. Under continuous UV irradiation, we observe vacancies/voids generated in the vicinity of NiO/perovskite heterojunction. Time-resolved femtosecond transient absorption and double-ion injection current measurements indicate UV irradiation would induce interface shallow traps and severe ion migration. These UV-induced degradations can be greatly suppressed by modifying the heterojunction with a self-assembled monolayer [2-(9 H-Carbazol-9-yl)ethyl] phosphonic acid (2PACz). Unencapsulated NiO/2PACz devices, operated at maximum power point (MPP), retain over 90% of their initial efficiency after exposing to a total UV dose of 35 kWh/m2. The best-performing device reaches a stabilized efficiency of 22.2%, and retains 82% of its original efficiency after 2000 h of MPP tracking under one sun illumination (100 mW/cm2) at 45 ℃ in ambient air when encapsulated.

Short-Lived Electron Excitations in FeTe1 –xSex as Revealed by Microwave Absorption

The $\rm Fe_{1+y}Te_{1-x}Se_x$\ single crystals with the various Se/Te ratios were studied by the microwave absorption and direct current resistivity measurements. The comparison of the microwave absorption data and the resistivity versus temperature made it possible to separate the contributions of two types of spin fluctuations. One of them is due to the anisotropic magnetic (nematic) fluctuations. It is observed over the wide temperature range from 30K to 150 or 200K. In FeSe it has the maximum close to the structural transition temperature. Another MWA anomaly is located in the narrow temperature range above the superconducting transition. It is likely due to the antiferromagnetic fluctuations. Annealing of a sample at the temperature around 300 C in the oxygen atmosphere made it possible to exclude the effect of excess iron on the observed anomalies.

Study of the effects of various parameters on the transient current on In2O3:Sn filler effect in epoxy resin for dielectric application

Epoxy resin nanocomposites with In2O3 doped 15% Sn (ITO) as nanofillers were fabricated to investigate the relationship between the polarization and depolarization current (PDC). The PDC, time to frequency domain transformation, dielectric parameters, charge carrier mobility and absorption current of epoxy nanocomposites samples are discussed. It is observed that the current magnitude increases in the nanocomposites with loading of nano-ITO than that of pure epoxy. While the current behavior through the epoxy decreases with time in a conventional manner, all nanocomposites reveal a decrease equally. Absorption current is an important characteristic of polymers with regard to their time domain response at direct field. The results of absorption current measurements can be used to understand the relationship between space charge accumulation and movement. The charge accumulation is likely to be influenced by the presence of charge trapping sites, which are associated with interactions between the nanoparticles and amorphous phases. The presence of such interfaces will affect the current flow due to the modification of the distribution of trapping sites within the material. Our results indicate that the absorption current behavior was affected by the added nano-ITO in epoxy matrix.

Absorption current behaviour of polyethylene/silica nanocomposites

Absorption current is an important characteristic of polymers with regard to their time-domain response to a direct current (DC) poling field. This is because the results of absorption current measurements can be used to gain understanding of the relationship between space charge accumulation and movement. In semicrystalline polyethylene, for example, charge accumulation is likely to be influenced by the presence of charge trapping sites, which are associated with interfaces between the crystalline and amorphous phases. With the addition of a nanofiller, the charge transport mechanism will become more complicated than in the unfilled polymer, as the inclusion of the nanofiller will introduce nanofiller/polymer interfaces. The presence of such interfaces will affect the current flow due to the introduction or modification of the distribution of trapping sites within the system. In this paper, we report on an investigation into the absorption current behaviour of polyethylene nanocomposites containing 0 wt%, 2 wt%, 5 wt% and 10 wt% of silica nanofiller, either untreated or treated using trimethoxy(propyl)silane coupling agent. Our results indicate that the absorption current behaviour of the polyethylene was affected by the presence of the nanosilica. While the current behaviour through the unfilled polymer decreases with time in a conventional manner, all nanocomposites reveal an initial decrease followed by a period in which the current increases with increasing time of DC field application.

Improvement in light harvesting and performance of P3HT:PCBM solar cell by using 9,10-diphenylanthracene

We have studied the effect of 9,10-diphenylanthracene (DPA) as a conjugated dye with different concentrations on light harvesting and performance of solar cell composed from poly (3-hexylthiophene) (P3HT):[6,6]-phenyl-C 61butyric acid methyl ester (PCBM) blend films. The dye concentration effect was investigated with optical absorption spectroscopy, photocurrent spectroscopy, and current density-voltage characteristic measurements on devices under AM1.5 white light illumination with intensity of 100 mW/cm 2. The incorporation of the conjugated DPA inside P3HT:PCBM blend improved the light harvesting, slightly, and conjugation length indicated from the optical absorption and external quantum efficiency spectra. By adding specific amounts of the DPA into P3HT:PCBM blend, the external quantum efficiency and solar cell performance parameters, i.e., short circuit current density, fill factor, and power conversion efficiency improved as a result of improvement in the light harvesting and charge carrier transfer taking place between P3HT and PCBM through the conjugated DPA molecules.

The mechanisms leading to the useful electrical properties of polymer nanodielectrics

Polymer nanocomposites with metal oxide nanoparticle fillers exhibit enhanced electrical breakdown strength and voltage endurance compared to their unfilled or micron filled counterparts. This paper presents the following hypothesis for the mechanisms leading to improved properties. The inclusion of nanoparticles provides myriad scattering obstacles and trap sites in the charge carriers' paths, effectively reducing carrier mobility and thus carrier energy. The result is homocharge buildup at the electrodes, which increases the voltage required for further charge injection due to blocking by the homocharge. The hypothesis is supported by electroluminescence, pulsed electro acoustic analysis, thermally stimulated current measurements, a comparison of AC, DC, and impulse breakdown, as well as absorption current measurements, in silica/crosslinked polyethylene matrix composites with supporting evidence from titania/epoxy composites.

Candidate mechanisms controlling the electrical characteristics of silica/XLPE nanodielectrics

The incorporation of silica nanoparticles into polyethylene has been shown to increase the breakdown strength significantly compared to composites with micron scale fillers. Additionally, the voltage endurance of the nanocomposites is two orders of magnitude higher than that of the base polymer. The most significant difference between micron-scale and nano-scale fillers is the large interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, this paper compares the behavior of nanoscale silica/cross-linked low density polyethylene nanocomposites with several silica surface treatments. In addition to breakdown strength and voltage endurance, dielectric spectroscopy, absorption current measurements, and thermally stimulated current determinations (TSC) were performed to elucidate the role of the interface. It was found that a reduction in the mobility in nanocomposites as well as a change in the defect size may be key to explaining the improvement in the properties.

In-line channel power monitor based on helium ion implantation in silicon-on-insulator waveguides

We propose and demonstrate an in-line channel power monitor (ICPM) based on helium ion implanted silicon waveguides. The implanted waveguide can detect light at below-bandgap wavelengths (1440-1590 nm) which are normally not detectable by silicon. We study the enhanced photoresponse of helium ion implanted samples which were annealed at 200 degC, 300 degC, or 350 degC for different durations. Optical absorption and photodetector current measurements were performed for each sample. The ICPM can provide the same function as a waveguide tap coupler and a hybrid-integrated conventional photodiode

Electrical properties of solid-phase crystallized polycrystalline silicon films

Analyses of free-carrier optical absorption and Hall-effect current measurements indicated in high carrier mobilities of 32 cm2/Vs and 30 cm2/Vs, respectively, and low carrier densities of 5.0×1019 cm-3 and 3.8×1019 cm-3, respectively, for 1.1×1020 cm-3-phosphorus-doped solid-phase crystallized polycrystalline silicon films fabricated at 600 °C for 48 h. The silicon films had good crystalline properties of the crystalline grains and a low crystalline volume fraction of 0.43. A XeCl excimer laser anneal at 500 mJ/cm2 effectively increased the carrier density to 1.1×1020 cm-3, and also increased the crystalline volume fraction to 0.93. Moreover, H2O-vapor heat treatment at 1.3×106 Pa for 3 h at 260 °C reduced the density of the defect states from 6.2×1018 cm-3 to 2.6×1018 cm-3.

Characterization of Liquid‐Crystal Materials for Low‐Voltage Operation TFT‐TN and IPS LCDs concerning Ions contained

AbstractIons contained in polar LC substances are characterized from absorption current measurements. Fluorinated and cyano LC substances were well characterized with regard to the Δ∍ values and ions contained, when used in cells with alignment materials. The results were applied to mixture design for use in low‐voltage operation TFT‐TN and TFT‐IPS LCDs, confirming the superiority of fluorinated LC substances for TFT‐TN‐LCDs and providing a new concept of mixtures composed of both fluorinated and cyano substances for a TFT‐IPS‐LCD use, featuring fast switching, low threshold voltage, and good voltage holding.

Absorption current and depolarisation measurements on polypropylene film

The authors report absorption and resorption current measurements on low-loss polypropylene over ranges of 10 mu s to 25 h, 0.5 to 2 MV cm-1, and -175 to 100 degrees C. While the resorption transients always decay hyperbolically, above 20 degrees C the absorption transients develop a conduction tail which is insensitive to contact metal. The current is resolved into volume and surface components, whose variation with time, field and temperature is illustrated. TSD measurements show no significant charge injection from Al contacts, but electron-beam-induced depolarisation experiments disclose heterocharge. Very deep electron traps (depth >or approximately=0.9 eV) and, tentatively, hole traps approximately=0.75 eV deep are identified by TSD on electron-bombarded films. All the observations point to an ionic mechanism, with a threshold related to glass transition, for the conduction tail.

Contact-injected Space Charge in Pet

Absorption current (step-voltage response) measurements complemented by electron-beam and thermally stimulated depolarization experiments on Melinex PET films under stresses of the order 100 MV/m are summarized. They provide clear evidence of field and temperature dependent injection of electronic carriers from metal contacts, leading to the formation of stored space charge. Al, Zn, Sb and In inject predominantly electrons but also, albeit weakly, holes. Au injects only weakly and only holes. The range of electrons trapped beneath an Al cathode is found to be ? 1 ?m at room temperature and 100 MV/m. The results confirm the conclusions drawn by previous authors, that any quasi-steady conduction observed in Melinex PET at high fields is likely to be contact-induced.

Relaxation Spectroscopy of the Dielectric β-Relaxation in Poly(n-alkyl methacrylate)s by Absorption–Current Measurements. I. Dielectric Relaxation Spectra for Atactic Polymers

In order to determine the dielectric relaxation spectra for the β-processes in atactic poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-propyl methacrylate) (PnPMA), and poly(n-butyl methacrylate) (PnBMA) which were sufficiently separated from the α-processes, absorption current was measured for 10 to 600 s after application of a step voltage at temperatures well below the glass transition temperatures. By applying the Hamon approximation, the data on time dependence of the absorption current were converted to those on the frequency dependence of loss permittivity, and the latter were reduced to master curves by the method of reduced variables. Shift factors gave an activation energy of ca. 19 kcal mol−1 irrespective of the side-chain length. Shapes of the β-relaxation spectra for these polymers were the same, but the relaxation strengths for PMMA, PEMA, PnPMA, and PnBMA were in the ratios 1:0.8:0.6:0.5, which correspond to the ratios of their dipolar densities. The β-relaxation spectrum began to sharpen with the increase in temperature above a critical temperature, which was estimated for PMMA and PEMA to be ca. 10 and 18°C respectively. A two-site model analysis suggests that the scale of the molecular process for the β-relaxation is as large as a 180°-rotation of the side group about the C-C bond connecting it to the main chain.

High field absorption current and space charge measurements on thin films of As 2S 3

The absorption current in evaporated and blown films of As 2S 3 decays approximately as 1/ t. The decay is conclusively shown not to be due to barrier polarization. Substantial space charge accumulation occurs subsequently without further current decay. Rectification in evaporated films at high fields is attributed to non-glassy structure.

A simple circuit for the production of a high voltage step

Describes the development of a circuit and switch capable of producing a highly stable step voltage of up to 30 kV, with a switching time of 1 ms. The design allows absorption current measurements to be made which are not possible at low voltages on certain dielectric materials.

Conduction in polythene with strong electric fields and the effect of prestressing on the electric strength

There has been speculation in the past about the extent to which space charge formed by the flow of prebreakdown current affects the electric strength of polythene. In the present work, conduction and absorption-current measurements up to about half the breakdown field have given clear evidence of space-charge effects. Further evidence was obtained from measurements of the apparent ‘intrinsic’ electric strength under various modes of stressing. It was found that the electric strength of polythene measured with direct voltage below about 30°C exceeded the corresponding value measured with impulse voltages by up to about 25% The impulse electric strength could be increased to equal the direct voltage by prestressing each specimen for 4min with direct voltage of the same polarity as the impulse voltage. However, when the impulse was of opposite polarity to the direct prestressing voltage, the electric strength decreased with increase in the prestressing field. The effect was dramatic, for the impulse electric strength changed from the normal value of about 6MV cm−1 to less than 2MV cm−1 as the prestressing field was increased to about 75% of the electric stength measured with direct voltage. Experiments in which the breakdown impulse was applied some time after removal of the prestressing field showed that the impulse electric strength at 20°C recovered in about 10−2s to the value obtained with impulses without prestressing. Thus the prestressing caused no permanent damage. The observed effects are attributed to space-charge injection from the electrodes. The observations are not consistent with the concept that breakdown occurs when the field at a point within the specimen exceeds a critical value, the intrinsic electric strength of polythene.

A Method for Calculating Dielectric Loss Factor from Absorption Current Measurements

A Method for Calculating Dielectric Loss Factor from Absorption Current Measurements