This article reviews some of our recent progress on materials design guidelines for photoinduced charge generation in bulk-heterojunction organic solar cells. Over the last 7 years, our group has ...employed transient absorption measurement to determine the relative quantum yields of long-lived polaron pairs for over 300 different organic Donor/Acceptor blend films. We have shown that this optical assay of charge separation can be a strong indicator of photocurrent generation efficiency in complete devices. In this review, we consider the lessons that can be drawn from these studies concerning the parameters that determine efficiency of this photoinduced charge separation in such solar cells. We consistently find, from studies of several materials series, that the energy offset driving charge separation is a key determinant of the efficiency of this charge generation, and thereby photocurrent generation. Moreover, we find that the magnitude of the energy offset required to drive charge separation, and the strength of this energetic dependence, varies substantially between materials classes. In particular, copolymers such as diketopyrrolopyrrole- and thiazolothiazole-based polymers are found to be capable of driving charge separation in blends with PCBM at much lower energy offsets than polythiophenes, such as P3HT, while replacement of PCBM with more crystalline perylene diimide acceptors is also observed to reduce the energy offset requirement for charge separation. We go on to discuss the role of film microstructure in also determining the efficiency of charge separation, including the role of mixed and pure domains, PCBM exciton diffusion limitations and the role of material crystallinity in modulating material energetics, thereby providing additional energy offsets that can stabilize the spatial separation of charges. Other factors considered include the role of Coulombically bound polaron pair or charge transfer states, device electric fields, charge carrier mobilities, triplet excitons, and photon energy. We discuss briefly a model for charge separation consistent with these and other observations. We conclude by summarizing the materials design guidelines for efficient charge photogeneration that can be drawn from these studies.
A study has been conducted of the plant biodiversity of the vascular plants in the Rilsko Korito valley. As a result, there were established 81 families, 327 genera and 639 vascular plant species. ...The floristic analysis performed determined the floristic elements, biological type and floristic complex of the examined local flora. The performed research managed to establish 1 Bulgarian endemite Muscari vandasii Velen. and 16 Balcan endemites. Eight species with conservation statuses were confirmed: critically endangered (CR) -Dactylorhiza kalopissii subsp. macedonica (J. Holz. & Kunkele) Kreutz, endangered (EN) – Epipactis palustris (L.) Crantz, Ophrys apifera Huds., vulnerable (VU) -Anacamptis pyramidalis (L.) Rich., Orchis laxiflora Lam. subsp. palustris (Jacq.) Bornm. et Lay., data-deficient (DD) - Typha schuttlewortii Koch. et Sond., least concern (LC) - Fritillaria pontica Wahlenb. and Ficus carica L. There were also 189 medicinal species were also determined (33.7% of the total number of species).
The occurrence of residual stresses in selective laser melting (SLM) presents challenges that limit the capability of the process to manufacture parts at industrial scale. These stresses can have ...irreversible effects such as warping and cracking of parts during and post manufacturing. One of the most important SLM parameters that should be controlled carefully in order to effectively manage residual stresses is the scanning strategy. This study presents an evaluation of four different scanning strategies, namely the island, successive, successive chessboard and least heat influence (LHI) scanning strategies with respect to their influence on residual stresses and distortions. All the scanning strategies were investigated by melting single tracks on tool steel substrates without powder. Measurement of residual stresses was performed on selected positions on the substrates before and after exposure to the laser beam using the x-ray diffraction technique. The successive chessboard scanning strategy was found to contribute to the least average residual stresses, and lowered residual stress by up to 40% relative to the default island scanning strategy. Further to this, the influence of the successive chessboard and island scanning strategies on distortions was evaluated. Similar to the residual stress findings, the successive chessboard contributed to lower form deviations compared to the island strategy. The scanning strategies were also evaluated based on their impact on total scanning times, with the successive chessboard strategy showing slightly lower scanning time than that for the island and LHI chessboard strategies.
Existence of spintronic memristor in nanoscale is demonstrated based upon spin-torque-induced magnetization switching and magnetic-domain-wall motion. Our examples show that memristive effects are ...quite universal for spin-torque spintronic device at the time scale that explicitly involves the interactions between magnetization dynamics and electronic charge transport. We also proved that the spintronic device can be designed to explore and memorize the continuum state of current and voltage based on interactions of electron and spin transport.
Solution-processed organic photovoltaics (OPV) offer the attractive prospect of low-cost, light-weight and environmentally benign solar energy production. The highest efficiency OPV at present use ...low-bandgap donor polymers, many of which suffer from problems with stability and synthetic scalability. They also rely on fullerene-based acceptors, which themselves have issues with cost, stability and limited spectral absorption. Here we present a new non-fullerene acceptor that has been specifically designed to give improved performance alongside the wide bandgap donor poly(3-hexylthiophene), a polymer with significantly better prospects for commercial OPV due to its relative scalability and stability. Thanks to the well-matched optoelectronic and morphological properties of these materials, efficiencies of 6.4% are achieved which is the highest reported for fullerene-free P3HT devices. In addition, dramatically improved air stability is demonstrated relative to other high-efficiency OPV, showing the excellent potential of this new material combination for future technological applications.
In recent years, there has been a significant surge in interest in measuring low radon levels in the environment. These measurements are valuable, particularly for identifying radon priority areas as ...required by the European Council Directive 2013/59/EURATOM and for research related to climate change. Due to the limited sensitivity of existing radon detectors/monitors in addressing these challenges, substantial efforts have been devoted to developing new designs. This report compares the sensitivity of several innovative designs with that of existing passive radon monitors. These novel designs incorporate alpha track detectors, including large area low background detectors, with activated carbon fabric used as an efficient radon adsorber/radiator. Recent innovative solutions to mitigate the impact of temperature and humidity on detectors using adsorbers are also discussed. The background signal of detectors intended for use in these novel designs is examined, and their sensitivity is evaluated. The findings demonstrate that these novel designs have the potential to significantly enhance the sensitivity of long-term radon measurements, surpassing the detectors currently in widespread use by more than an order of magnitude.
•The sensitivity of novel passive radon detectors has been estimated and compared to that of existing models.•The novel detectors combine activated carbon fabric, used as adsorbers/radiators, with track detectors.•The sensitivity of novel detectors may exceed that of existing models by 1-2 orders of magnitude.•The highest sensitivity, even under high humidity conditions, is achieved with the fabric ACC-5092-10.
Aims. Most hot Jupiters are expected to spiral in toward their host stars because the angular momentum of the orbital motion is transferred to the stellar spin. Their orbits can also precess as a ...result of planet-star interactions. Calculations show that both effects might be detected for the very-hot exoplanet WASP-12 b using the method of precise transit-timing over a time span of about 10 yr. Methods. We acquired new precise light curves for 29 transits of WASP-12 b, spannning four observing seasons from November 2012 to February 2016. New mid-transit times, together with those from the literature, were used to refine the transit ephemeris and analyze the timing residuals. Results. We find that the transit times of WASP-12 b do not follow a linear ephemeris with a 5σ confidence level. They may be approximated with a quadratic ephemeris that gives a change rate in the orbital period of (−2.56 ± 0.40) × 10-2 s yr-1. The tidal quality parameter of the host star was found to be equal to 2.5 × 105, which is similar to theoretical predictions for Sun-like stars. We also considered a model in which the observed timing residuals are interpreted as a result of the apsidal precession. We find, however, that this model is statistically less probable than the orbital decay.
Hemolytic diseases are frequently linked to multiorgan failure subsequent to vascular damage. Deciphering the mechanisms leading to organ injury upon hemolytic event could bring out therapeutic ...approaches. Complement system activation occurs in hemolytic disorders, such as sickle cell disease, but the pathological relevance and the acquisition of a complement-activating phenotype during hemolysis remain unclear. Here we found that intravascular hemolysis, induced by injection of phenylhydrazine, resulted in increased alanine aminotransferase plasma levels and NGAL expression. This liver damage was at least in part complement-dependent, since it was attenuated in complement C3−/− mice and by injection of C5-blocking antibody. We evidenced C3 activation fragments’ deposits on liver endothelium in mice with intravascular hemolysis or injected with heme as well as on cultured human endothelial cells (EC) exposed to heme. This process was mediated by TLR4 signaling, as revealed by pharmacological blockade and TLR4 deficiency in mice. Mechanistically, TLR4-dependent surface expression of P-selectin triggered an unconventional mechanism of complement activation by noncovalent anchoring of C3 activation fragments, including the typical fluid-phase C3(H₂O), measured by surface plasmon resonance and flow cytometry. P-selectin blockade by an antibody prevented complement deposits and attenuated the liver stress response, measured by NGAL expression, in the hemolytic mice. In conclusion, these results revealed the critical impact of the triad TLR4/P-selectin/complement in the liver damage and its relevance for hemolytic diseases. We anticipate that blockade of TLR4, P-selectin, or the complement system could prevent liver injury in hemolytic diseases like sickle cell disease.
We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the ...synthesis of DTBT monomers with either 0, 1, or 2 cyano groups on the BT unit and their corresponding copolymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor–acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ∼0.25 eV upon addition of each cyano group, while the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the monocyano substituted BT polymer. However, the PCE drops to less than 1% for the dicyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by 1 order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in the photocurrent was investigated by studying the charge generation properties of the photoactive polymer–fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties while maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer’s light harvesting properties were improved without sacrificing either the exciton dissociation yield or device V OC. We also identify that the drop in performance for the 2CN polymer is caused by very limited yields of electron transfer from the polymer to the fullerene, likely caused by poor orbital energy level alignment with the fullerene acceptor (PC71BM). This work highlights the impact that small changes in chemical structure can have on the optoelectronic and device properties of semiconducting polymer. In particular this work highlights the effect of LUMO–LUMO offset on the excited state dynamics of polymer–fullerene blends.
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