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The current density–voltage characteristic (J–V) is a critical tool for understanding the behavior of solar cells. This study presents an overview of the key aspects of J–V analysis and introduces a user‐friendly flowchart that facilitates the swift identification of the most probable limiting process in a solar cell, based mainly on the outcomes of light‐intensity‐dependent J–V measurements. The flowchart is developed through extensive drift‐diffusion simulations and a rigorous review of the literature, with a specific focus on perovskite and organic solar cells. Moreover, the flowchart proposes supplementary experiments that can be conducted to obtain a more precise prediction of the primary performance losses. It therefore serves as an optimal starting point to analyse performance losses of solar cells. [ABSTRACT FROM AUTHOR]

Organic semiconductors are excellent candidates for low temperature thermoelectric generators. However, such thermoelectric applications require materials be doped and highly conductive. Here, we show how doping affects the Seebeck coefficient in organic semiconductors using kinetic Monte Carlo simulations. Employing a hopping transport approach, we demonstrate that at high dopant loading, carrier–carrier interactions can reduce the Seebeck coefficient. This results in systems with intrinsic disorder, still following Heike's formula for thermopower at high dopant density. Reducing these carrier–carrier interactions results in an increased Seebeck coefficient and power factor. Specifically, a realistic reduction in carrier–carrier interactions can increase the power factor by more than a factor 15, increasing ZT above 1 for organic thermoelectrics. [ABSTRACT FROM AUTHOR]

We use a Monte Carlo model to predict the effect of composition, domain size, and energetic disorder upon the mobility of carriers in an organic donor-acceptor blend. These simulations show that, for the changes in local morphology expected within the thickness of a typical bulk heterojunction photovoltaic device, changes in mobility of more than an order of magnitude are expected. The impact of nonuniform mobility upon space-charge-limited diode and photovoltaic (PV) device performance is examined using a drift-diffusion model. The current passing through a space-charge-limited diode is shown to depend upon the position of the layers with differing mobility. Accurate modeling of the current in such devices can only be achieved using a drift-diffusion model incorporating nonuniform mobility. Inserting a 20 nm thick layer in which the mobility is less by one order of magnitude than in the rest of the 70 nm thick PV device reduced the device efficiency by more than 20%. Therefore it seems vital to exert a high degree of control over the morphology throughout the entire blend PV device, otherwise potential PV performance may be lost. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of solar cells based on a conjugated polymer (donor) and a fullerene derivative (acceptor) is very sensitive to the morphology of the active layer. One detrimental feature, which is often encountered in non-optimal morphologies, is the occurrence of fullerene blobs in a finely mixed matrix containing both donor and acceptor material. Here, the effects of such fullerene blobs are studied in detail with a three-dimensional drift-diffusion model. It includes the effects of exciton diffusion and quenching; space-charge; recombination, generation, drift and diffusion of charge carriers; and the injection/extraction of carriers at the contacts. The influence of blob size and shape, and matrix composition are quantified. The latter has the strongest effect on the overall efficiency, as most of the current is transported through the mixed phase. The total current flowing out of the solar cell can be split up in a part which comes from the interfacial region between the acceptor phase and the mixed phase, and a part that stems from the mixed phase itself. Depending on the bias voltage and the morphology, one or the other contribution is dominant. Finally, it is shown how both contributions can be computed with a simple one-dimensional drift-diffusion simulator. [ABSTRACT FROM AUTHOR]

To determine the role of photon energy on charge generation in bulk heterojunction solar cells, the bias voltage dependence of photocurrent for excitation with photon energies below and above the optical band gap is investigated in two structurally related polymer solar cells. Charges generated in (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′′]dithiophene)-alt-4,7-(2,1,3-benzothia­diazole)] (C-PCPDTBT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solar cells via excitation of the low-energy charge transfer (CT) state, situated below the optical band gap, need more voltage to be extracted than charges generated with excitation above the optical band gap. This indicates a lower effective binding energy of the photogenerated electrons and holes when the excitation is above the optical band gap than when excitation is to the bottom of the CT state. In blends of PCBM with the silicon-analogue, poly[(4,4-bis(2-ethylhexyl)dithieno[3,2- b:2 ′,3 ′- d]silole)-2,6-diyl- alt-(2,1,3-benzothiadiazole)-4,7-diyl] (Si-PCPDTBT), there is no effect of the photon energy on the electric field dependence of the dissociation efficiency of the CT state. C-PCPDTBT and Si-PCPDTBT have very similar electronic properties, but their blends with PCBM differ in the nanoscale phase separation. The morphology is coarser and more crystalline in Si-PCPDTBT:PCBM blends. The results demonstrate that the nanomorphological properties of the bulk heterojunction are important for determining the effective binding energy in the generation of free charges at the heterojunction. [ABSTRACT FROM AUTHOR]

The performance of polymer solar cells critically depends on the morphology of the interface between the donor- and acceptor materials that are used to create and transport charge carriers. Solar cells based on poly(3-hexylthiophene) and ZnO were fully characterized in terms of their efficiency and three-dimensional (3D) morphology on the nanoscale. Here, we establish a quantitative link between efficiency and morphology by using the experimental 3D morphology as direct input for a 3D optoelectronic device model. This model includes the effects of exciton diffusion and quenching; space-charge; recombination, generation, drift and diffusion of charge carriers; and the injection/extraction of carriers at the contacts. The observed trend in internal quantum efficiency as a function of layer thickness is reproduced with a single set of parameters. Several morphological aspects that determine the internal quantum efficiency are discussed and compared to other organic solar cells. This first direct use of morphological data in an optoelectronic device model highlights the importance of morphology in solar cells. [ABSTRACT FROM AUTHOR]

Three different theoretical approaches are presented to identify pathways to organic solar cells with power conversion efficiencies in excess of 20%. A radiation limit for organic solar cells is introduced that elucidates the role of charge-transfer (CT) state absorption. Provided this CT action is sufficiently weak, organic solar cells can be as efficient as their inorganic counterparts. Next, a model based on Marcus theory of electronic transfer that also considers exciton generation in both the electron donor and electron acceptor is used to show how reduction of the reorganization energies can lead to substantial efficiency gains. Finally, the dielectric constant is introduced as a central parameter for efficient solar cells. By using a drift-diffusion model, it is found that efficiencies of more than 20% are within reach. [ABSTRACT FROM AUTHOR]

We determine and analyze the photocurrent Jph in polymer solar cells under conditions where, no, one, or two different charge carriers can be injected by choosing appropriate electrodes and compare the experimental results to simulations based on a drift-diffusion device model that accounts for photogeneration and Langevin recombination of electrons and holes. We demonstrate that accounting for the series resistance of the device is essential to determine Jph. Without such correction, the results are, even qualitatively, incorrect. We show that in solar cells with forward bias applied 7ph is reduced by recombination of photogenerated charge carriers with injected charge carriers. Self-selective contacts or band bending are not necessary to explain the effects. Without injecting contacts Jpb is symmetric around the compensation voltage. A simple analytical model shows that under high forward bias Jpt, scales inversely with 1 + ξγpre, in which γpre represents the extent of Langevin recombination and ξ is a positive constant. Under conditions where Langevin recombination is very low or when electron and hole mobility are a very different, photogenerated charge carriers can affect the space-charge field and modify the injection of charge carriers. We show by simulations and experimentally that under such conditions the photocurrent can exceed that charge generation such that, effectively, photocurrent multiplication occurs. [ABSTRACT FROM AUTHOR]

The trap-assisted recombination of electrons and holes in organic semiconductors is investigated. The extracted capture coefficients of the trap-assisted recombination process are thermally activated with an identical activation energy as measured for the hole mobility μp. We demonstrate that the rate limiting step for this mechanism is the diffusion of free holes towards trapped electrons in their mutual Coulomb field, with the capture coefficient given by (q/ε)μp. As a result, both the bimolecular and trap-assisted recombination processes in organic semiconductors are governed by the charge carrier mobilities, allowing predictive modeling of organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

We present a scaling theory for charge transport in disordered molecular semiconductors that extends percolation theory by including bonds with conductances close to the percolating one in the random-resistor network representing charge hopping. A general and compact expression is given for the charge mobility for Miller-Abrahams and Marcus hopping on different lattices with Gaussian energy disorder, with parameters determined from numerically exact results. The charge-concentration dependence is universal. The model-specific temperature dependence can be used to distinguish between the hopping models. [ABSTRACT FROM AUTHOR]

it is controversial whether energetic disorder in semiconductors is already sufficient to violate the classical Einstein relation, even in the case of thermal equilibrium. We demonstrate that the Einstein relation is violated only under nonequilibrium conditions due to deeply trapped carriers, as in diffusion- driven current measurements on organic single-carrier diodes. Removal of these deeply trapped carriers by recombination unambiguously proves the validity of the Einstein relation in disordered semiconductors in thermal (quasi)equilibrium. [ABSTRACT FROM AUTHOR]

In organic semiconductors the recombination mechanism is of the Langevin type, controlled by the mobility of the charge carriers. As a result, in organic solar cells the mobility simultaneously controls both the carrier extraction and the losses via carrier recombination. The authors demonstrate that the balance between carrier losses by extraction and by recombination leads to a distinct optimum in the carrier mobility with regard to the efficiency of organic solar cells. For low mobilities recombination losses limit the performance, whereas the efficient extraction at high mobilities leads to a reduction of the open-circuit voltage. [ABSTRACT FROM AUTHOR]

We study the thickness dependence of the performance of bulk heterojunction solar cells based on poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] as electron donor and [6,6]-phenyl C61 butyric acid methyl ester as electron acceptor. Typically, these devices have an active layer thickness of 100 nm at which only 60% of the incoming light is absorbed. Increasing device thickness results in a lower overall power conversion efficiency, mainly due to a lowering of the fill factor. We demonstrate that the decrease in fill factor and hence device efficiency is due to a combination of charge recombination and space-charge effects. [ABSTRACT FROM AUTHOR]

We present model calculations to explore the potential of polymer/fullerene bulk heterojunction solar cells. As a starting point, devices based on poly(3-hexylthiophene) and 6,6-phenyl C61-butyric acid methyl ester (PCBM), reaching 3.5% efficiency, are modeled. Lowering the polymeric band gap will lead to a device efficiency exceeding 6%. Tuning the electronic levels of PCBM in such a way that less energy is lost in the electron transfer process enhances the efficiency to values in excess of 8%. Ultimately, with an optimized level tuning, band gap, and balanced mobilities polymeric solar cells can reach power conversion efficiencies approaching 11%. [ABSTRACT FROM AUTHOR]

Bimolecular recombination in organic semiconductors is known to follow the Langevin expression, i.e., the rate of recombination depends on the sum of the mobilities of both carriers. We show that this does not hold for polymer/fullerene bulk heterojunction solar cells. The voltage dependence of the photocurrent reveals that the recombination rate in these blends is determined by the slowest charge carrier only, as a consequence of the confinement of both types of carriers to two different phases. [ABSTRACT FROM AUTHOR]

A typical feature of polymer/fullerene based solar cells is that the current density under short-circuit conditions (Jsc) does not scale exactly linearly with light intensity (I). Instead, a power law relationship is found given by Jsc∝Iα, where α ranges from 0.85 to 1. In a number of reports this deviation from unity is speculated to arise from the occurrence of bimolecular recombination. We demonstrate that the dependence of the photocurrent in bulk heterojunction solar cells is governed by the build-up of space-charge in the device as a consequence of a difference in electron- and hole mobility. We have verified this for an experimental model system in which the mobility difference can be tuned from one to three orders of magnitude by changing the annealing treatment. [ABSTRACT FROM AUTHOR]

The open-circuit voltage Voc of polymer:fullerene bulk heterojunction solar cells is investigated as a function of light intensity for different temperatures. Devices consisted of a blend of a poly(p-phenylene vinylene) derivative as the hole conductor and 6,6-phenyl C61-butyric acid methyl ester as the electron conductor. The observed photogenerated current and Voc are at variance with classical p–n junction-based models. The influence of light intensity and recombination strength on Voc is consistently explained by a model based on the notion that the quasi-Fermi levels are constant throughout the device, including both drift and diffusion of charge carriers. [ABSTRACT FROM AUTHOR]

An increase in the workfunction of the metal top electrode leads to a reduction of the open-circuit voltage, short-circuit current, and power conversion efficiency of organic bulk-heterojunction solar cells. It has been demonstrated that the photocurrent obtained from an active layer comprised of a blend of poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylene vinylene) (OC1C10-PPV) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM), with lithium fluoride topped aluminum, silver, gold, or palladium electrodes, shows a universal behavior when scaled against the effective voltage across the device. Indeed, model calculations confirm that the dependence of the photocurrent on the effective voltage is responsible for the observed variation in performance of each different electrode. Consequently, for any given metal, only the device’s open-circuit voltage is required in order to be able to predict the remaining solar cell parameters. [ABSTRACT FROM AUTHOR]

Energy‐harvesting technologies offer a sustainable, maintenance‐free alternative to conventional energy‐storage solutions in distributed low‐power applications. Flexible thermoelectric generators (TEGs) can generate electric power from a temperature gradient, even on complex surfaces. Organic materials are ideal candidates for flexible TEGs due to their good solution‐processability, natural abundance, low weight, and flexibility. Electronic and thermoelectric properties of organic materials have steadily progressed, while device architectures leveraging their advantages are largely missing. Here, a design and fabrication method are proposed for producing fully screen‐printed, flexible monolithic organic TEGs scalable up to m2, compatible with any screen‐printable ink. This approach is validated, along with its scalability, by printing TEGs composed of two different active inks, in three configurations, with up to 800 thermoelements, with performances well matching simulations based on materials parameters. It is demonstrated that by using an additive‐free graphene ink, a remarkable power density of 15 nW cm−2 at ΔT = 29.5 K can be achieved, with an estimated weight‐normalized power output of 1 µW g−1, highlighting a strong potential in portability. Owing to such power density, only limited areas are required to generate microwatts, sufficient for operating low‐power electronic devices such as sensors, and wearables. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in‐plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6‐tetrafluoro‐tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight‐fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll‐off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices. [ABSTRACT FROM AUTHOR]

Charge transport properties are investigated of blends of poly [2-methoxy-5-(3′, 7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) and poly-[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3′, 7′-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV). The hole transport in the MDMO-PPV donor phase of the 1:1 weight ratio blend is trap-free space-charge limited, with a mobility identical to the pristine polymer. The electron current in the PCNEPV acceptor phase is strongly reduced by traps that are exponentially distributed in energy. The current in MDMO-PPV:PCNEPV bulk heterojunction solar cells is therefore unbalanced and dominated by the holes in the MDMO-PPV phase. [ABSTRACT FROM AUTHOR]

Two chimeric antigen receptor (CAR) T-cell therapies - Tisagenlecleucel (Kymriah™) and Axicabtagene ciloleucel (Yescarta™) - have been approved for commercial use. In order to inform forthcoming EBMT guidelines on the management of adults and children undergoing autologous CAR T-cell therapy, we undertook a survey of experienced clinicians. An online survey with a dual focus on (1) 'real world' patient eligibility criteria and (2) models of care for patient follow-up was sent to experienced physicians. There were 41 respondents (10 countries) and 93% worked in FACT-JACIE-accredited transplant centres. Most felt that a history of malignancy (57%), prior allo-HCT for B-NHL (78%–81%) and prior treatment with anti-CD19/CD3 BiTE antibodies (76%–86%) do not constitute contra-indications to CAR T therapy. Clinicians were divided as to whether CNS involvement represented an exclusion criterion. There was agreement that patients with viral infections (HIV, Hepatitis B or Hepatitis C) are not eligible. There is no common model of care for long-term follow-up. Most respondents believed that patients should attend the hospital two (43%) to three (33%) times weekly during the first month following discharge. A majority (69%) of respondents work in centres where there is an MDT meeting with a specific focus on follow-up following CAR T Therapy. Follow-up care is currently delivered either in HCT or haematology-oncology outpatient clinics. The responses reveal wide variation in perceived patient eligibility criteria and highlight the need for consensus guidelines. The findings also illustrate the embryonic nature of current follow-up arrangements. [ABSTRACT FROM AUTHOR]

Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k2 = 1.7 × 10−17 m3 s−1. BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. [ABSTRACT FROM AUTHOR]

Understanding the relationship between the absorber layer microstructure and the power conversion efficiency is of paramount importance to further improve the efficiency of organic solar cells. Utilizing transmission electron microscopy (TEM), (photo-)conductive atomic force microscopy ((p)cAFM), 3D drift-diffusion simulations, and density functional theory, we reveal the microscopic origins of phase-separation in a blend of zinc phthalocyanine (ZnPc) and C 60 , used as an absorber layer in organic solar cells. By means of (p)cAFM, we observe photoconductive, circular structures at the surface, which are identified as α -ZnPc islands. Moreover, in agreement with TEM investigations, we observe photoconductive, nanorod-like structures close to the surface which we assign to β -ZnPc. Finally, we apply a 3D drift-diffusion simulation based on the morphology determined by TEM to provide a link between the different contrasts observed in pcAFM and TEM. [ABSTRACT FROM AUTHOR]

The performance of organic bulk heterojunction solar cells is strongly dependent on the donor/acceptor morphology. Morphological parameters, such as the extent and the composition of donor- and acceptor-rich domains, influence both the charge generation and the charge transport throughout the active layer. This work focuses on a polymer:fullerene system based on a small bandgap diketopyrrolopyrrole–quinquethiophene alternating copolymer (PDPP5T) mixed with [6,6]-phenyl-C 71 -butyric acid methyl ester ([70]PCBM) that is capable of efficiencies higher than 6%. By changing the processing conditions, the morphology can be varied from a coarse separated morphology, with fullerene domains (blobs) embedded in a polymer-rich matrix, to a completely mixed layer. The charge carrier transport and the strength of the bimolecular recombination in PDPP5T:[70]PCBM blends with different morphologies and fullerene concentrations are experimentally characterized. The large difference in electron and hole mobility and the electric field dependency of the electron mobility are identified as the causes that limit the performance of devices with low [70]PCBM content. These effects are not present if the concentration of [70]PCBM is increased while keeping a fine phase separation by the addition of ortho -dichlorobenzene as a cosolvent. For the phase-separated blends, a model is proposed, based on a drift–diffusion approach that combines electrical and morphological parameters; with this model the contribution of each phase to the total current is quantified. Under operating conditions, most of the current comes from the interfacial region between the phases, with holes traveling through the matrix and the electrons through the blobs. This device model consistently connects morphological features to overall device performance. [ABSTRACT FROM AUTHOR]

A steady‐state method to probe bimolecular recombination in organic solar cells is presented. The technique is applicable to thin‐film solar cells at any temperature and does not require a separate measurement setup other than conventional solar‐cell testing equipment. The key element in our method is the derivation of a simple analytical expression that directly gives access to the recombination strength. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Abnormal temporal and spatial sensory integration have been described in mixed groups of dystonic patients. We tested somatosensory integration and the effect of botulinum toxin (BoNT) in patients with writer’s cramp (WC). Methods: Median and ulnar SEPs were recorded in 29 WC patients and in 10 controls. We performed: individual and simultaneous stimulation of median and ulnar nerves (MU) and paired stimulation of median nerve at interstimulus-interval (ISI) of 40 and 100ms. All the trials were repeated after blinded randomized treatment with placebo or BoNT-A. Results: We found no differences between patients and controls in standard SEPs. Spatial (except for N9) and temporal suppression after ISI 40 were present in both groups for all the waves; after ISI 100, suppression was present only for N70. There were no differences between patients and controls. After BoNT-A treatment, no changes were observed. Conclusions: In contrast with previous findings in heterogeneous dystonic groups, and although some studies suggest impairment of spatial and temporal sensory discrimination in patients with focal dystonia, in our large cohort of patients with WC we found no evidence of abnormal somatosensory integration investigated by means of SEPs and no changes in somatosensory variables after BoNT-A treatment. Significance: Our findings may suggest pathophysiological differences between focal and generalized dystonia, and may also point to an inferior sensitivity of SEPs in detecting abnormalities in sensory discrimination as compared to methods based on subjective discrimination. [Copyright &y& Elsevier]

summary: The iron plaque on roots of Aster tripolium L. growing in waterlogged salt marsh soil adsorbed appreciable amounts of Zn and Cu, with maximum Zn/Fe and Cu/Fe ratios of 0.1 When concentrations of Zn or Cu adsorbed in the iron plaque are expressed as mg metal kg−1 FeOOH (assuming that iron plaque consists mainly of FeOOH), the Zn and Cu concentrations of the iron plaque was up to 680 and up to 2000 times higher than in the surrounding sediment, respectively. The Zn concentration in red roots (with iron plaque) was higher than in white roots (without iron plaque). Zn concentrations in field sampled roots were correlated with the amount of Zn on the roots and the Zn concentration in the soil, whereas Cu concentrations in the roots were only significantly correlated to the Cu concentration in the soil. In vitro experiments showed that red roots take up more Zn than white roots. Measurement of Zn uptake by excised roots showed that the uptake of Zn into the xylem fluid was significantly higher in roots with 500–2000 nmol Fe cm−2 on the root surface compared to roots with less than 500 or more than 2000 nmol Fe cm−2 on the root surface. The results indicate that iron plaque enhances uptake of Zn by the roots but may act as a barrier when large amounts of Fe are deposited on the root surface. The role of the iron plaque on roots of salt marsh plants growing in soil contaminated with heavy metals is discussed. [ABSTRACT FROM AUTHOR]

The iron plaque on roots of Aster tripolium L. growing in waterlogged salt marsh soil adsorbed appreciable amounts of Zn and Cu, with maximum Zn/Fe and Cu/Fe ratios of 0.1. When concentrations of Zn or Cu adsorbed in the iron plaque are expressed as mg metal kg-1 FeOOH (assuming that iron plaque consists mainly of FeOOH), the Zn and Cu concentrations of the iron plaque was up to 680 and up to 2900 times higher than in the surrounding sediment, respectively. The Zn concentration in red roots (with iron plaque) was higher than in white roots (without iron plaque). Zn concentrations in field sampled roots were correlated with the amount of Zn on the roots and the Zn concentration in the soil, whereas Cu concentrations in the roots were only significantly correlated to the Cu concentration in the soil. In vitro experiments showed that red roots take up more Zn than white roots. Measurement of Zn uptake by excised roots showed that the uptake of Zn into the xylem fluid was significantly higher in roots with 500-2000 nmol Fe cm-2 on the root surface compared to roots with less than 500 or more than 2000 nmol Fe cm-2 on the root surface. The results indicate that iron plaque enhances uptake of Zn by the roots but may act as a barrier when large amounts of Fe are deposited on the root surface. The role of the Iron plaque on roots of salt marsh plants growing in soil contaminated with heavy metals is discussed. [ABSTRACT FROM AUTHOR]

Blends of semiconducting (SC) and ferroelectric (FE) polymers have been proposed for applications in resistive memories and organic photovoltaics (OPV). For OPV, the rationale is that the local electric field associated with the dipoles in a blend could aid exciton dissociation, thus improving power conversion efficiency. However, FE polymers either require solvents or processing steps that are incompatible with those required for SC polymers. To overcome this limitation, SC (poly(3‐hexylthiophene)) and FE (poly(vinylidene fluoride‐trifluoroethylene)) components are incorporated into a block copolymer and thus a path to a facile fabrication of smooth thin films from suitably chosen solvents is achieved. In this work, the photophysical properties and device performance of organic solar cells containing the aforementioned block copolymer consisting of poly(vinylidene fluoride‐trifluoroethylene): P(VDF‐TrFE), poly(3‐hexylthiophene): P3HT and the electron acceptor phenyl‐C61‐butyric acid methyl ester: [60]PCBM are explored. A decrease in photovoltaic performance is observed in blends of the copolymer with P3HT:[60]PCBM, which is attributed to a less favorable nanomorphology upon addition of the copolymer. The role of lithium fluoride (the cathode modification layer) is also clarified in devices containing the copolymer, and it is demonstrated that ferroelectric compensation prevents the ferroelectricity of the copolymer from improving photovoltaic performance in SC‐FE blends. [ABSTRACT FROM AUTHOR]

Next-generation organic photovoltaic technology is currently geared towards non-fullerene organic solar cells. Among the non-fullerene small molecule acceptors, ITIC derivatives play a central role with power conversion efficiency above 15% in single junction cells. However, knowledge about the stability of these new types of devices is lagging behind, creating an efficiency-lifetime gap for commercial viability. Here, we study the photostability of three ITIC derivatives, namely ITIC together with IT-M and IT-F, representative of methylated and halogenated ITIC, the usual modification to this small molecule acceptor. While the best performing solar cell yields a PCE of 8.6%, we find that the photostability of the devices greatly depends on the structure of the acceptor and the configuration of the devices. The methylation of ITIC into IT-M improves V oc but does not greatly affect the photostability of the devices. While fluorination generally decreases the efficiency of the cells, the stability of the fluorinated ITIC-based cells appears to depend on the device structure. Thus, the change from ITIC to IT-F may not in all cases necessarily be beneficial to the advancement of the technology. Subtle changes in molecular structure coupled with imbalance charge mobilities is at the origin of the observed differences in degradation. Image 1 • The effect of the energy modulation of ITIC derivatives on polymer solar cell performance. • The fluorination of ITIC small molecule acceptor into IT-F reduces the V oc of the solar cells. • The addition of methyl groups onto ITIC to form IT-M increases the V oc of the solar cells. • IT-M has no significant effect on the photostability. • The photostability of IT-F-based cell depends on the device structure. [ABSTRACT FROM AUTHOR]

Abstract: The low power conversion efficiency (PCE) of tin‐based hybrid perovskite solar cells (HPSCs) is mainly attributed to the high background carrier density due to a high density of intrinsic defects such as Sn vacancies and oxidized species (Sn4+) that characterize Sn‐based HPSCs. Herein, this study reports on the successful reduction of the background carrier density by more than one order of magnitude by depositing near‐single‐crystalline formamidinium tin iodide (FASnI3) films with the orthorhombic a‐axis in the out‐of‐plane direction. Using these highly crystalline films, obtained by mixing a very small amount (0.08 m) of layered (2D) Sn perovskite with 0.92 m (3D) FASnI3, for the first time a PCE as high as 9.0% in a planar p–i–n device structure is achieved. These devices display negligible hysteresis and light soaking, as they benefit from very low trap‐assisted recombination, low shunt losses, and more efficient charge collection. This represents a 50% improvement in PCE compared to the best reference cell based on a pure FASnI3 film using SnF2 as a reducing agent. Moreover, the 2D/3D‐based HPSCs show considerable improved stability due to the enhanced robustness of the perovskite film compared to the reference cell. [ABSTRACT FROM AUTHOR]

The mechanism behind the temperature dependence of the device performance in hybrid perovskite solar cells (HPSCs) is investigated systematically. The power conversion efficiency (PCE) of the reference cell using [60]PCBM as electron extraction layer (EEL) drops significantly from 11.9% at 295 K to 7% at 180 K. The deteriorated charge carrier extraction is found as the dominant factor causing this degradation. Temperature dependent spectroscopy and charge transport studies demonstrate that the poor electron transport in the [60]PCBM EEL at low temperature leads to inefficient charge carrier extraction. It is further demonstrated that the n-type doping of [60]PCBM EEL or the use of an EEL (fulleropyrrolidine with a triethylene glycol monoethyl ether side chain) with higher electron transport capability is an effective strategy to achieve HPSCs working efficiently over a broad temperature range. The devices fabricated with these highly performing EELs have PCEs at 180 K of 16.7% and 18.2%, respectively. These results support the idea that the temperature dependence of the electron transport in the EELs limits the device performance in HPSCs, especially at lower temperatures and they also give directions toward further improvement of the PCE of HPSCs at realistic operating temperatures. [ABSTRACT FROM AUTHOR]

Charge transport in organic photovoltaic (OPV) devices is often characterized by steady-state mobilities. However, the suitability of steady-state mobilities to describe charge transport has recently been called into question, and it has been argued that dispersion plays a significant role. In this paper, the importance of the dispersion of charge carrier motion on the performance of organic photovoltaic devices is investigated. An experiment to measure the charge extraction time under realistic operating conditions is set up. This experiment is applied to different blends and shows that extraction time is directly related to the geometrical average of the steady-state mobilities. This demonstrates that under realistic operating conditions the steady-state mobilities govern the charge extraction of OPV and gives a valuable insight in device performance. [ABSTRACT FROM AUTHOR]

To improve the efficiency of existing perovskite solar cells (PSCs), a detailed understanding of the underlying device physics during their operation is essential. Here, a device model has been developed and validated that describes the operation of PSCs and quantitatively explains the role of contacts, the electron and hole transport layers, charge generation, drift and diffusion of charge carriers and recombination. The simulation to the experimental data of vacuum-deposited CH3NH3PbI3 solar cells over multiple thicknesses has been fit and the device behavior under different operating conditions has been studied to delineate the influence of the external bias, charge-carrier mobilities, energetic barriers for charge injection/extraction and, different recombination channels on the solar cell performance. By doing so, a unique set of material parameters and physical processes that describe these solar cells is identified. Trap-assisted recombination at material interfaces is the dominant recombination channel limiting device performance and passivation of traps increases the power conversion efficiency (PCE) of these devices by 40%. Finally, guidelines to increase their performance have been issued and it is shown that a PCE beyond 25% is within reach. [ABSTRACT FROM AUTHOR]

Despite the rich experience gained in controlling the microstructure of perovskite films over the past several years, little is known about how the microstructure affects the device properties of perovskite solar cells (HPSCs). In this work, the effects of the perovskite film microstructure on the charge recombination and light-soaking phenomenon in mixed halide HPSCs are investigated. Devices with noncompact perovskite morphology show a severe light soaking effect, with the power conversion efficiency (PCE) improved from 3.7% to 11.6% after light soaking. Devices with compact perovskite morphology show a negligible light soaking effect, with PCE slightly increased from 11.4% to 11.9% after light soaking. From device investigations, photoluminescence, and impedance spectroscopy measurements, it is demonstrated that interface electron traps at the grain boundaries as well as at the crystal surface dominate the light soaking effect. Severe trap-assisted recombination takes place in HPSCs using noncompact films, while it is effectively eliminated in devices with compact films. Moreover, how the grain size of the perovskite film affects the light soaking phenomenon is investigated. In the case of compact perovskite films, the size of the grains has a limited effect on the light soaking. In these compact films, grains are fused and trap states are effectively reduced. [ABSTRACT FROM AUTHOR]

The rapid degradation of organic photovoltaic (OPV) devices compared to conventional inorganic solar cells is one of the critical issues that have to be solved in order to make OPV a competitive commercial technology. The understanding of the fundamental mechanisms that reduce the power con- version efficiency (PCE) over time is beneficial for the design of new materials with enhanced stability. This paper focuses on bulk heterojunction organic solar cells based on thieno [3,4-b] thiophene-alt-benzodithiophene (PTB7) mixed with [6,6]-phenyl-C71-butyric acid methyl esther ([70]PCBM). In spite of being promising in terms of PCE, devices based on this blend are unstable and have a short lifetime. When exposed to light in inert atmosphere, the PCE drops by 15% in less than 1 h and by 35% in 8 h; this degradation is induced by the ultraviolet (UV) part of the spectrum. This paper analyzes the effect induced by UV light on the transport of charges in PTB7:[70]PCBM. Contrary to expectations, the electron transport shows evidence of trapping, while the transport of holes appears unaffected. Furthermore, it is proven that the loss of PCE is due to a reaction between PTB7 and [70]PCBM, while the intrinsic instability of the polymer plays a marginal role. [ABSTRACT FROM AUTHOR]

To eliminate quenching of excitons at the metallic cathode of a polymer light-emitting diode (PLED) the emitting layer is separated from the cathode by a hole-blocking layer (HBL). We investigate a wide range of single-layer and bilayer PLEDs with different thicknesses consisting of a poly[2-methoxy-5-(2′-ethylhexyloxy)- p -phenylene vinylene] (MEH-PPV) emitting layer and a 20 nm poly(9,9′-dioctylfluorene) (PFO) HBL. The highest efficiency for both single-layer and bilayer devices is achieved when the total polymer layer thickness is ∼90 nm. As a result, addition of an HBL to reduce cathode quenching is only effective when the luminescence enhancement due to microcavity effects in PLEDs is restored. The relative efficiency enhancement in bilayer devices as compared to single-layer devices varies from 283% for a 30 nm active layer to 20% for a 250 nm device. [ABSTRACT FROM AUTHOR]

Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, εr) in the range of 2-4. As a consequence, Coulombically bound electron-hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance εr of well-known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of εr together with poly( p-phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of εr with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl-C61-butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents. [ABSTRACT FROM AUTHOR]

Time-delayed collection field (TDCF) and bias-amplified charge extraction (BACE) are applied to as-prepared and annealed poly(3-hexylthiophene):[6,6]-phenyl C71 butyric acid methyl ester (P3HT:PCBM) blends coated from chloroform. Despite large differences in fill factor, short-circuit current, and power conversion efficiency, both blends exhibit a negligible dependence of photogeneration on the electric field and strictly bimolecular recombination (BMR) with a weak dependence of the BMR coefficient on charge density. Drift-diffusion simulations are performed using the measured coefficients and mobilities, taking into account bimolecular recombination and the possible effects of surface recombination. The excellent agreement between the simulation and the experimental data for an intensity range covering two orders of magnitude indicates that a field-independent generation rate and a density-independent recombination coefficient describe the current-voltage characteristics of the annealed P3HT:PCBM devices, while the performance of the as-prepared blend is shown to be limited by space charge effects due to a low hole mobility. Finally, even though the bimolecular recombination coefficient is small, surface recombination is found to be a negligible loss mechanism in these solar cells. [ABSTRACT FROM AUTHOR]

The first case of pandemic H1N1 influenza (pH1N1) virus in feral swine in the United States was identified in Texas through the United States Department of Agriculture (USDA) Wildlife Services' surveillance program. Two samples were identified as pandemic influenza by reverse transcriptase quantitative PCR (RT-qPCR). Full-genome Sanger sequencing of all eight influenza segments was performed. In addition, Illumina deep sequencing of the original diagnostic samples and their respective virus isolation cultures were performed to assess the feasibility of using an unbiased whole-genome linear target amplification method and multiple sample sequencing in a single Illumina GAIIx lane. Identical sequences were obtained using both techniques. Phylogenetic analysis indicated that all gene segments belonged to the pH1N1 (2009) lineage. In conclusion, we have identified the first pH1N1 isolate in feral swine in the United States and have demonstrated the use of an easy unbiased linear amplification method for deep sequencing of multiple samples. [ABSTRACT FROM AUTHOR]

We provide a short review of modern ‘plastic’ solar cells, a broad topic that spans materials science, physics, and chemistry. The aim of this review is to provide a primer for non-experts or researchers in related fields who are curious about this rapidly growing field of interdisciplinary research. We introduce the basic concepts of plastic solar cells and design rules for maximizing their efficiency, including modern quantum chemical calculations that can aide in the design of new materials. We discuss the history of the materials and modern trends in polymeric donor materials and fullerene acceptors, and provide demonstrative data from hybrid polymer/quantum dot devices. [Copyright &y& Elsevier]

A multiscale approach to the description of geometrically complex 3D image data is proposed which distinguishes between morphological features on a 'macro-scale' and a 'micro-scale'. Since our method is mainly tailored to nanostructures observed in composite materials consisting of two different phases, an appropriate binarization of grayscale images is required first. Then, a morphological smoothing is applied to extract the structural information from binarized image data on the 'macro-scale'. A stochastic algorithm is developed for the morphologically smoothed images whose goal is to find a suitable representation of the macro-scale structure by unions of overlapping spheres. Such representations can be interpreted as marked point patterns. They lead to an enormous reduction of data and allow the application of well-known tools from point-process theory for their analysis and structural modeling. All those voxels which have been 'misspecified' by the morphological smoothing and subsequent representation by unions of overlapping spheres are interpreted as 'micro-scale' structure. The exemplary data sets considered in this paper are 3D grayscale images of photoactive layers in hybrid solar cells gained by electron tomography. These composite materials consist of two phases: a polymer phase and a zinc oxide phase. The macro-scale structure of the latter is represented by unions of overlapping spheres. [ABSTRACT FROM AUTHOR]

In 2007, Vietnam experienced swine disease outbreaks causing clinical signs similar to the ‘porcine high fever disease’ that occurred in China during 2006. Analysis of diagnostic samples from the disease outbreaks in Vietnam identified porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2). Additionally, Escherichia coli and Streptococcus equi subspecies zooepidemicus were cultured from lung and spleen, and Streptococcus suis from one spleen sample. Genetic characterization of the Vietnamese PRRSV isolates revealed that this virus belongs to the North American genotype (type 2) with a high nucleotide identity to the recently reported Chinese strains. Amino acid sequence in the nsp2 region revealed 95.7–99.4% identity to Chinese strain HUN4, 68–69% identity to strain VR-2332 and 58–59% identity to strain MN184. A partial deletion in the nsp2 gene was detected; however, this deletion did not appear to enhance the virus pathogenicity in the inoculated pigs. Animal inoculation studies were conducted to determine the pathogenicity of PRRSV and to identify other possible agents present in the original specimens. Pigs inoculated with PRRSV alone and their contacts showed persistent fever, and two of five pigs developed cough, neurological signs and swollen joints. Necropsy examination showed mild to moderate bronchopneumonia, enlarged lymph nodes, fibrinous pericarditis and polyarthritis. PRRSV was re-isolated from blood and tissues of the inoculated and contact pigs. Pigs inoculated with lung and spleen tissue homogenates from sick pigs from Vietnam developed high fever, septicaemia, and died acutely within 72 h, while their contact pigs showed no clinical signs throughout the experiment. Streptococcus equi subspecies zooepidemicus was cultured, and PRRSV was re-isolated only from the inoculated pigs. Results suggest that the cause of the swine deaths in Vietnam is a multifactorial syndrome with PRRSV as a major factor. [ABSTRACT FROM AUTHOR]

The efficiency of polymer solar cells critically depends on the intimacy of mixing of the donor and acceptor semiconductors used in these devices to create charges and on the presence of unhindered percolation pathways in the individual components to transport holes and electrons. The visualization of these bulk heterojunction morphologies in three dimensions has been challenging and has hampered progress in this area. Here, we spatially resolve the morphology of 2%-efficient hybrid solar cells consisting of poly(3-hexylthiophene) as the donor and ZnO as the acceptor in the nanometre range by electron tomography. The morphology is statistically analysed for spherical contact distance and percolation pathways. Together with solving the three-dimensional exciton-diffusion equation, a consistent and quantitative correlation between solar-cell performance, photophysical data and the three-dimensional morphology has been obtained for devices with different layer thicknesses that enables differentiating between generation and transport as limiting factors to performance. [ABSTRACT FROM AUTHOR]

The invention of new organic materials with high dielectric constants is of extreme importance for the development of organic-based devices such as organic solar cells. We report on a synthetic way to increase the dielectric constant of fullerene derivatives. It is demonstrated that introducing triethylene glycol monoethyl ether (teg) side chains into fulleropyrrolidines increases the dielectric constant by ~46 percent without devaluation of optical properties, electron mobility and the energy level of the compound. [ABSTRACT FROM AUTHOR]

The origin of the enhanced performance of bulk heterojunction solar cells based on slowly dried films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester is investigated, combining charge transport measurements with numerical device simulations. Slow drying leads to a 33-fold enhancement of the hole mobility up to 5.0×10-7 m2 V-1 s-1 in the P3HT phase of the blend, thereby balancing the transport of electrons and holes in the blend. The resulting reduction of space-charge accumulation enables the use of thick films (∼300 nm), absorbing most of the incoming photons, without losses in the fill factor and short-circuit current of the device. [ABSTRACT FROM AUTHOR]