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The subgranular zone (SGZ) of the hippocampal dentate gyrus (DG) is a neurogenic niche of the adult brain that contains neural stem cells (NSCs) able to generate excitatory glutamatergic granule neurons, which integrate into the DG circuit and contribute to hippocampal plasticity, learning, and memory. Thus, endogenous NSCs could be harnessed for therapeutic purposes. In this context, it is critical to characterize the molecular mechanisms controlling the generation and functional integration of adult-born neurons. Adult hippocampal neurogenesis is tightly controlled by both cell-autonomous mechanisms and the interaction with the complex niche microenvironment, which harbors the NSCs and provides the signals to support their maintenance, activation, and differentiation. Among niche-derived factors, Wnt ligands play diverse roles. Wnts are secreted glycoproteins that bind to Frizzled receptors and co-receptors to trigger the Wnt signaling pathway. Here, we summarize the current knowledge about the roles of Wnts in the regulation of adult hippocampal neurogenesis. We discuss the possible contribution of the different niche cells to the regulation of local Wnt signaling activity, and how Wnts derived from different cell types could induce differential effects. Finally, we discuss how the effects of Wnt signaling on hippocampal network activity might contribute to neurogenesis regulation. Although the evidence supports relevant roles for Wnt signaling in adult hippocampal neurogenesis, defining the cellular source and the mechanisms controlling secretion and diffusion of Wnts will be crucial to further understand Wnt signaling regulation of adult NSCs, and eventually, to propose this pathway as a therapeutic target to promote neurogenesis.

In Alzheimer´s disease (AD) there is a reduction in hippocampal neurogenesis that has been associated to cognitive deficits. Previously we showed that Andrographolide (ANDRO), the main bioactive component of Andrographis paniculate, induces proliferation in the hippocampus of the APPswe/PSEN1ΔE9 (APP/PS1) mouse model of AD as assessed by staining with the mitotic marker Ki67. Here, we further characterized the effect of ANDRO on hippocampal neurogenesis in APP/PS1 mice and evaluated the contribution of this process to the cognitive effect of ANDRO. Treatment of 8-month-old APP/PS1 mice with ANDRO for 4 weeks increased proliferation in the dentate gyrus as evaluated by BrdU incorporation. Although ANDRO had no effect on neuronal differentiation of newborn cells, it strongly increased neural progenitors, neuroblasts and newborn immature neurons, cell populations that were decreased in APP/PS1 mice compared to age-matched wild-type mice. ANDRO had no effect on migration or in total dendritic length, arborization and orientation of immature neurons, suggesting no effects on early morphological development of newborn neurons. Finally, ANDRO treatment improved the performance of APP/PS1 mice in the object location memory task. This effect was not completely prevented by co-treatment with the anti-mitotic drug TMZ, suggesting that other effects of ANDRO in addition to the increase in neurogenesis might underlie the observed cognitive improvement. Altogether, our data indicate that in APP/PS1 mice ANDRO stimulates neurogenesis in the hippocampus by inducing proliferation of neural precursor cells and improves spatial memory performance.

Indexación Scopus Wnt signaling plays a key role in neurodevelopment and neuronal maturation. Specifically, Wnt5a stimulates postsynaptic assemblies, increases glutamatergic neurotransmission and, through calcium signaling, generates nitric oxide (NO). Trying to unveil the molecular pathway triggering these postsynaptic effects, we found that Wnt5a treatment induces a time-dependent increases in the length of the postsynaptic density (PSD), elicits novel synaptic contacts and facilitates F-actin flow both in in vitro and ex vivo models. These effects were partially abolished by the inhibition of the Heme-regulated eukaryotic initiation factor 2α (HRI) kinase, a kinase which phosphorylates the initiation translational factor eIF2α. When phosphorylated, eIF2α normally avoids the translation of proteins not needed during stress conditions, in order to avoid unnecessary energetic expenses. However, phosphorylated eIF2α promotes the translation of some proteins with more than one open reading frame in its 5′ untranslated region. One of these proteins targeted by Wnt-HRI-eIF2α mediated translation is the GluN2B subunit of the NMDA receptor. The identified increase in GluN2B expression correlated with increased NMDA receptor function. Considering that NMDA receptors are crucial for excitatory synaptic transmission, the molecular pathway described here contributes to the understanding of the fast and plastic translational mechanisms activated during learning and memory processes. © 2021, The Author(s). https://www-nature-com.recursosbiblioteca.unab.cl/articles/s41598-021-86708-y

Background Cognitive dysfunction (CD) is common among patients with the autoimmune disease systemic lupus erythematosus (SLE). Anti-ribosomal P autoantibodies associate with this dysfunction and have neuropathogenic effects that are mediated by cross-reacting with neuronal surface P antigen (NSPA) protein. Elucidating the function of NSPA can then reveal CD pathogenic mechanisms and treatment opportunities. In the brain, NSPA somehow contributes to glutamatergic NMDA receptor (NMDAR) activity in synaptic plasticity and memory. Here we analyze the consequences of NSPA absence in KO mice considering its structural features shared with E3 ubiquitin ligases and the crucial role of ubiquitination in synaptic plasticity. Results Electrophysiological studies revealed a decreased long-term potentiation in CA3-CA1 and medial perforant pathway-dentate gyrus (MPP-DG) hippocampal circuits, reflecting glutamatergic synaptic plasticity impairment in NSPA-KO mice. The hippocampal dentate gyrus of these mice showed a lower number of Arc-positive cells indicative of decreased synaptic activity and also showed proliferation defects of neural progenitors underlying less adult neurogenesis. All this translates into poor spatial and recognition memory when NSPA is absent. A cell-based assay demonstrated ubiquitination of NSPA as a property of RBR-type E3 ligases, while biochemical analysis of synaptic regions disclosed the tyrosine phosphatase PTPMEG as a potential substrate. Mice lacking NSPA have increased levels of PTPMEG due to its reduced ubiquitination and proteasomal degradation, which correlated with lower levels of GluN2A and GluN2B NMDAR subunits only at postsynaptic densities (PSDs), indicating selective trafficking of these proteins out of PSDs. As both GluN2A and GluN2B interact with PTPMEG, tyrosine (Tyr) dephosphorylation likely drives their endocytic removal from the PSD. Actually, immunoblot analysis showed reduced phosphorylation of the GluN2B endocytic signal Tyr1472 in NSPA-KO mice. Conclusions NSPA contributes to hippocampal plasticity and memory processes ensuring appropriate levels of adult neurogenesis and PSD-located NMDAR. PTPMEG qualifies as NSPA ubiquitination substrate that regulates Tyr phosphorylation-dependent NMDAR stability at PSDs. The NSPA/PTPMEG pathway emerges as a new regulator of glutamatergic transmission and plasticity and may provide mechanistic clues and therapeutic opportunities for anti-P-mediated pathogenicity in SLE, a still unmet need.

Capacitive response at long time scales seems to remain an elusive feature in the analysis of the electrical properties of perovskite-based solar cells. It belongs to one of the critical anomalous effects that arises from the characteristic phenomenology of this type of emerging photovoltaic devices. Thereby, accurately deducing key capacitance feature of new light harvesting perovskites from electrical measurements represents a significant challenge regarding the interpretation of physical processes and the control of undesired mechanisms, such as slow dynamic effects and/or current density–voltage (J–V) hysteresis. Herein, it is shown that long timescale mechanisms that give rise to hysteresis in stable and high-efficiency quadruple-cation perovskites are not due to a classical capacitive behavior in the sense of ideal charge accumulation processes. Instead, it is a phenomenological consequence of slow memory-based capacitive currents and the underlying cooperative relaxations. A fractional dynamics approach, based on the idea of capacitance distribution in perovskite devices, reliably models the slow transient phenomena and the consequent scan-rate- and bias-dependent hysteresis. Observable for a wide variety of photovoltaic halide perovskites, distributed capacitive effects are rather universal anomalous phenomena, which can be related to the long-time electrical response and hysteresis., This work was supported by Comunidad de Madrid under the SINFOTON2-CM Research Program, S2018/NMT4326-SINFOTON2-CM, the Ministerio de Economía, Industria y Competitividad, Project TEC2016-77242-C3-3-R, and the European Regional Development Fund (fondos FEDER). To the Ministerio de Ciencia e Innovación for the grant GraPErOs (ENE2016-79282-C5-2-R) and the Self-Power (PID2019-104272RB-C54). To the Agència de Gestiód'Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 217 SGR 329 and the Xarxa d'R+D+I Energy for Society (XRE4S). Part of this work is under Materials Science Ph.D. Degree for C.P. of the Universitat Autónoma de Barcelona. The authors thank CONACYT for the scholarship to C.P. ICN2 was supported by the Severo Ochoa program from MINECO (SEV-2017-0706) and was funded by the CERCA Programme/Generalitat de Catalunya.

In this work, we have studied degradation mechanisms of nonfullerene-based organic solar cells with PET/Ag/ZnO/PBDTB-T:ITIC/PEDOT:PSS/CPP PEDOT:PSS device structure. We compare pristine and degraded samples that were subjected to outdoor degradation following the standard ISOS-O2 protocol. The ideality factors for different incident wavelengths obtained from open-circuit voltage vs irradiation level and current density–voltage (J–V) measurements at different temperatures indicate that for aged samples recombination is governed by the Shockley–Read–Hall mechanism occurring in a region near the anode. Samples were also characterized using impedance spectroscopy (IS) and fitted to an electrical model. Impedance parameters were used to obtain mobility, indicating a clear degradation of the active layer blend for aged samples. The change in the chemical capacitance also reveals a worsening in carrier extraction. Finally, two-dimensional (2D) numerical simulations and fits to experimental J–V curves confirm the existence of a layer near the anode contact with poorer mobility and a decrease in the anode work function (WF) for the degraded samples. This work was supported by Comunidad de Madrid under the SINFOTON2-CM Research Program (S2018/NMT-4326-SINFOTON2-CM) and the Spanish Ministry of Economy, the Agencia Estatal de Investigación, and European Union's FEDER under the TEC2016−77242-C1/C2/C3 AEI/FEDER, UE Projects. The work of E.L.-F. was supported by the Ministerio de Educación y Formación Profesional for his Doctoral Grant through the FPU Research Fellowship under Grant FPU17/00612. M.M., J.L., E.D., and V.T. acknowledge that part of this work was developed within the RollFlex project, part-financed by Interreg Deutschland-Danmark with means from the European Regional Development Fund and the Southern Denmark Growth Forum. M.M. and V.T. acknowledge the support from the Villum Foundation for Project CompliantPV (Grant No. 13365). Finally, all authors acknowledge the support from the EU Framework Program Horizon 2020 for MNPS COST ACTION MP1307 StableNextSol. Publicado

In this work we study the degradation of roll-coated flexible inverted organic solar cells with the device architecture Ag/PEDOT:PSS/ZnO/FSP1:PCBM/PEDOT:PSS/Ag in different atmospheres. We demonstrate that impedance spectroscopy is a powerful tool for elucidating degradation mechanisms; it is used here to distinguish the different degradation mechanisms due to water and oxygen. Identical cells were exposed to different accelerated degradation environments using water only, oxygen only, and both water and oxygen simultaneously, all of them enhanced with UV light. The photocurrent is dramatically reduced in the oxygen-degraded samples. Impedance measurements indicate that this phenomenon is attributed to defects introduced by absorption of oxygen, which results in an increase of the acceptor impurity (NA) at the cathode interface obtained from a Mott-Schottky analysis. Simultaneously, at the anode interface where PEDOT:PSS is not shielded by the substrate, the nature of degradation differs for the water and oxygen degraded samples. While oxygen + UV light decreases the conductivity of the PEDOT:PSS layer, water + UV light changes the PEDOT:PSS work function inducing a depletion region at the anode.

Klotho is an aging-related protein associated with hippocampal cognitive performance in mammals. Klotho regulates progenitor cell proliferation in non-neuronal tissues, but its role in adult hippocampal neurogenesis (AHN) has not been explored. Klotho expression in the adult mouse hippocampus was examined by immunofluorescence and polymerase chain reaction. AHN was evaluated in the hippocampus of klotho knock-out mice (KO), klotho KO/vitamin D-receptor mutant mice, and in a model of local klotho hippocampal knockdown. The recombinant Klotho effect on proliferation was measured in mouse-derived hippocampal neural progenitor cells. Hippocampal-dependent memory was assessed by a dry-land version of the Morris water maze. Klotho was expressed in the granular cell layer of the adult Dentate Gyrus. AHN was increased in klotho KO mice, but not in klotho KO/vitamin D-receptor mutant mice. Inversely, local downregulation of hippocampal Klotho diminished AHN. Recombinant Klotho increased the proliferation rate of neural progenitors. Downregulation of hippocampal Klotho correlated with a decreased performance in hippocampal-dependent memory. These results suggest that Klotho directly participates in regulating AHN. Our observations indicate that Klotho promotes proliferation, AHN and hippocampal-dependent cognition. Increased neurogenesis in klotho KO mice may be secondary to the activation of other pathways altered in the model, such as vitamin D.

In this work PTB7:[70]PCBM (Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b] thiophenediyl]]:[6,6]-Phenyl-C71-butyric acid methyl-ester ([70])) based solar cells with PEIE (Polyethylenimine, 80% Ethoxylated) as electron transport layer (ETL) have been characterized along two months using impedance spectroscopy (IS). The experimental data were fitted using an electrical circuit and the time evolution of circuital parameters was analyzed. At high voltages, the capacitance associated to the PEIE layer decreases within the first days of measurements while the resistance increases during the same period. The flat band voltage, V fb , obtained from a Mott-Schottky analysis, decreases with measuring time around 0.1 V, suggesting a deterioration of PEIE interface that no longer improves the ITO work-function. Carrier mobility decreases from 2.2 × 10 −3 cm 2 /Vs to 2.4 × 10 −4 cm 2 /Vs within the first few days of measurements.

The potential opportunities of perovskite-based technology to further advance in the photovoltaic field and implement an extensive industrial application, will mainly depend on whether some of its weaknesses, such as current density-voltage (J−V) hysteresis, can be overcome. In this sense, a critical aspect is the understanding and the subsequent accurate description of hysteresis in perovskite cells. Here, we present the theoretical underpinnings to interpret non-ideal transient dynamics in stepwise-JV measurements, using electrical analysis strategies and fractional calculus tools. Our model was validated with experimental measurements of CsFAPbIBr-based photovoltaic perovskites of different active layer thicknesses with persistent long-range time photocurrents. It is reported that hysteresis phenomena increase with more pronounced non-ideal capacitive effects suggesting that more trapping events limit ion motion and carrier transport. Our main interest is to provide valuable information about the memory-based slow timescale dynamics, which exhibits a significant impact on the appearance of hysteresis and, to a large extent, on the operation of the solar cell.

Impedance Spectroscopy (IS) is a non-destructive characterization technique that has been extensively applied to different electronic devices, such as LEDs, photodiodes and solar cells. This technique provides access to valuable information about dynamical mechanisms (minority carrier recombination, diffusion, etc.) taking place in the different layers of the device. Besides, material and device parameters, such as dielectric constant, built-in potential, and carrier mobilities can be extracted. Impedance spectra results from applying a small AC signal over a steady DC bias and measuring the resulting small AC current over a frequency range, typically from 1 Hz to 1 MHz, 𝑍(jω) = VAC/1AC. The Nyquist plot of the complex impedance (imaginary part vs real part) generally presents one or more features (mainly semicircles), depending on the number of mechanisms governing the device. Fitting an electrical equivalent circuit to the complete impedance spectra provides parameters related to each feature (resistance and capacitance). In this work, IS has been used to characterize organic and perovskite solar cells (OSCs and PSCs, respectively). Measurements have been performed in dark and under illumination conditions at different bias (from 0 V to VOC). A simple circuital model containing two resistances and two capacitances has been used to fit the measured IS spectra. The interpretation of extracted circuital parameters and its relationship with the physical model of the device will be discussed.

In the adult hippocampus, new neurons are generated in the dentate gyrus. The Wnt signaling pathway regulates this process, but little is known about the endogenous Wnt ligands involved. We investigated the role of Wnt5a on adult hippocampal neurogenesis. Wnt5a regulates neuronal morphogenesis during embryonic development, and maintains dendritic architecture of pyramidal neurons in the adult hippocampus. Here, we determined that Wnt5a knockdown in the mouse dentate gyrus by lentivirus-mediated shRNA impaired neuronal differentiation of progenitor cells, and reduced dendritic development of adult-born neurons. In cultured adult hippocampal progenitors (AHPs), Wnt5a knockdown reduced neuronal differentiation and morphological development of AHP-derived neurons, whereas treatment with Wnt5a had the opposite effect. Interestingly, no changes in astrocytic differentiation were observed in vivo or in vitro, suggesting that Wnt5a does not affect fate-commitment. By using specific inhibitors, we determined that Wnt5a signals through CaMKII to induce neurogenesis, and promotes dendritic development of newborn neurons through activating Wnt/JNK and Wnt/CaMKII signaling. Our results indicate Wnt5a as a niche factor in the adult hippocampus that promotes neuronal differentiation and development through activation of noncanonical Wnt signaling pathways.

This article reviews and appraises the dc lumped-parameter equivalent circuit models that have been proposed so far for representing some types of solar cells that can exhibit under certain circumstances a detrimental S-shaped concave deformation within the energy-producing fourth quadrant of their illuminated I-V characteristics. We first present a very succinct recollection of lumped-parameter equivalent circuits that are commonly used to model conventional solar cells in general. We then chronologically present and discuss lumped-parameter equivalent sub-circuits that, combined with conventional solar cell equivalent circuits, are used to specifically represent the undesired S-shaped behaviour. The mathematically descriptive equations of each complete equivalent circuit are also examined, and closed form solutions for the terminal current and voltage as explicit functions of each other are presented and discussed whenever available. While comparing the most salient features and explaining the practical advantages and disadvantages of such equivalent circuit models, we offer some comments on possible directions for further improvement.

Perovskite-based solar cells are devices of increasing interest among new generation of photovoltaic technologies due to the outstanding power conversion efficiency (PCE) achieved in the last few years, and the favorable fabrication conditions. Among all these excellent photovoltaic properties, perovskite light-harvesting devices also show relevant issues such as the hysteresis mechanisms in the current density-voltage (J-V) characteristics, whose underlying origins have not yet been clarified from a single and universally accepted point of view. Here, we focus our attention on the ideal capacitive mechanisms which, on the other hand, are often modeled using fractional-order capacitors in the equivalent circuits used to fit impedance measurements. In particular, we provide the theoretical framework for the transient-photocurrent analysis described by fractional-order responses which involve the generalized Mittag-Leffler function. Importantly, the model introduces a connection between perovskite traps and defects, memory processes, fractional dynamics, and Cole-Cole behavior. Crucial dependences of non-ideal capacitive dynamics on fractional-order α and the selected scan rate were found in the J-V hysteresis behavior from the perspective of the non-integer order calculus. In this sense, it is necessary to point out that our numerical simulations of dark J-V curves by considering non-ideal capacitive effects reveal more prominent distortions than those of the ideal case, leading from free-hysteretic influences (α = 1) to significant hysteresis distortions (0

The past few years have seen a great increase in the development of Visible Light Communication systems (VLC), mainly triggered by the wide variety of situations they can be used in. These communication systems have traditionally employed inorganic light emitters and photodetectors. In this work, we present a VLC system using an organic emitter and a perovskite photodetector, both fabricated using low cost processing techniques. Perovskite devices have been widely studied as photovoltaics cells since they have achieved great efficiencies, and, in the recent years, there is also an intense research of these devices as photodetectors. In this work, we have fabricated and characterized a perovskite photodetector with layer structure ITO/PTAA/Perovskite/PCBM/BCP/Cu, and integrated it in a visible communication system to successfully link an audio signal.

Perovskite Solar Cells (PSC) have attracted great attention due to the high efficiencies achieved in the past few years (up to 24.2 %). Perovskite semiconductors show excellent light absorption and large charge-carrier mobilities. In addition, device fabrication is low cost and easily up-scalable. However, the current density-voltage curve (J-V) shows hysteresis and devices suffer from stability issues which are still poorly understood. Among all perovskite materials, mixed-cation lead mixed-halide PSC have become very popular due to their high efficiencies and reasonably good stabilities1,2. On the other hand, Impedance Spectroscopy (IS) is a very valuable non-destructive technique to obtain information about dynamical mechanisms occurring both in the bulk and at the interfaces3. In this work, J-V curves and the impedance response have been measured for CsFAPbIBr-based PSC from 1 Hz up to 1 MHz, under different illumination levels (from 0.06 mW/cm2 to 100 mW/cm2) both at 0 V (short circuit) and at Voc (open circuit). Impedance spectra show two significant arcs, associated to different recombination and charge accumulation mechanisms. IS data have been fitted to a circuital model that consists of a low-frequency RCPE subcircuit in series with a high frequency resistance, all shunted with a high-frequency capacitance. Dependence of the circuital parameters with Voc and Isc will be discussed.

Flexible inverted organic solar cells (OSC) based on Poly(3-hexylthiophene-2, 5-diyl): [6], [6]-Phenyl C61 butyric acid methyl ester (P3HT: PCBM) have been manufactured and degraded using two different degradation protocols: six cells were kept in dark conditions, according to ISOS-D1 protocol, while other six were placed outdoor in a solar tracker, according to ISOS-O1 protocol. Pristine and degraded devices have been characterized in terms of I-V curves and Impedance Spectroscopy (IS). After two months, the efficiency drops from 2.83 % to 2.55 % for devices kept in dark conditions, and to 0.85 % for devices placed outdoor. Impedance spectra, measured before and after degradation have been fitted with an equivalent circuit that models recombination and diffusion processes. The evolution of the circuital parameters obtained from the IS fit show that devices degraded outside present i) a significant increase of the transport resistance, which hinders charge conduction, and ii) a decrease of majority carrier mobility, which is related to a loss of the blend crystallinity.

Visible light communication systems can be used in a wide variety of applications, from driving to home automation. The use of wearables can increase the potential applications in indoor systems to send and receive specific and customized information. We have designed and developed a fully organic and flexible Visible Light Communication system using a flexible OLED, a flexible P3HT:PCBM-based organic photodiode (OPD) and flexible PCBs for the emitter and receiver conditioning circuits. We have fabricated and characterized the I-V curve, modulation response and impedance of the flexible OPD. As emitter we have used a commercial flexible organic luminaire with dimensions 99 &times, 99 &times, 0.88 mm, and we have characterized its modulation response. All the devices show frequency responses that allow operation over 40 kHz, thus enabling the transmission of high quality audio. Finally, we integrated the emitter and receiver components and its electronic drivers, to build an all-organic flexible VLC system capable of transmitting an audio file in real-time, as a proof of concept of the indoor capabilities of such a system.

Metabolic syndrome (MetS) is a global epidemic, which involves a spectrum of metabolic disorders comprising diabetes and obesity. The impact of MetS on the brain is becoming to be a concern, however, the poor understanding of mechanisms involved has limited the development of therapeutic strategies. We induced a MetS-like condition by exposing mice to fructose feeding for 7weeks. There was a dramatic deterioration in the capacity of the hippocampus to sustain synaptic plasticity in the forms of long-term potentiation (LTP) and long-term depression (LTD). Mice exposed to fructose showed a reduction in the number of contact zones and the size of postsynaptic densities (PSDs) in the hippocampus, as well as a decrease in hippocampal neurogenesis. There was an increase in lipid peroxidation likely associated with a deficiency in plasma membrane excitability. Consistent with an overall hippocampal dysfunction, there was a subsequent decrease in hippocampal dependent learning and memory performance, i.e., spatial learning and episodic memory. Most of the pathological sequel of MetS in the brain was reversed three month after discontinue fructose feeding. These results are novel to show that MetS triggers a cascade of molecular events, which disrupt hippocampal functional plasticity, and specific aspects of learning and memory function. The overall information raises concerns about the risk imposed by excessive fructose consumption on the pathology of neurological disorders.

Organic solar cells (OSCs) based on Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5, 5-(4', 7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (PCBM) have been electrically dc and ac characterized. Device structure is ITO/Poly(3,4-ethylenedioxy-wthiophene)-poly(4-styrene sulfonate) (PEDOT:PSS)/PCDTBT:PCBM/C60MA/Al. Devices show the so-called S-shaped current-voltage curve that has been modeled with a circuit including two diodes in forward and reverse bias. Impedance measurements show one semicircle at low bias ( V

International audience; In this work light activation phenomenon in inverted bulk heterojunction (BHJ) organic solar cells (OSC) has been electrically modelled with a two-diode equivalent circuit. OSC are based on poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (PCBM) with a titanium oxide (TiOx) sublayer. Current-voltage (I-V) characteristics show a highly pronounced S-shape that is gradually removed during light activation process. The circuit used to model I-V curves includes two diodes in forward and reverse bias together with two parallel resistances, RP 1 and RP 2. The parallel of the reverse bias diode and its corresponding resistance RP 2 models the electrical behaviour of the TiOx interlayer. This interlayer has been thermally treated at different temperatures, from 80 °C up to 180 °C, reducing the activation time from 400 s for unbaked devices down to 30 s for devices annealed at temperatures higher than 80 °C. The S-shape shown in the I-V characteristic is completely removed after a few minutes of white-light illumination. I-V curves recorded during the activation process have been fitted with the analytical solution of the two-diode circuit based on W-Lambert function. A decrease of the subcircuit 2 equivalent resistance has been found to be the cause of S-shape removal. This resistance diminishing is in good agreement with the increase of TiOx conductance with baking temperature and white-light exposure time found by other authors.

In this paper we study the transport-recombination mechanisms using impedance spectroscopy of organic solar cells (OSC) based on a blend of a small molecule, 7,7′-(4,4-bis(2ethylhexyl)-4H-silolo[3,2-b:4,5-b′] dithiophene-2,6-diyl)bis(6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5] thiadiazole) (DTS(FBTTh2)2) and 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C70 (PC70BM). We fabricate a cell with structure ITO/Poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate (PEDOT:PSS))/DTS(FBTTh2)2:PC70BM/Ca/Al that exhibits Jsc=10.2 mA/cm2, Voc=0.816 V and FF=65% resulting in a PCE=5.4%. We model the impedance behavior using two circuital models, the parallel R-CPE and the transmission line model proposed by Belmonte et al. [1] . We compared the results to those obtained for OSC based on a standard poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (PC60BM) blend with structure ITO/PEDOT:PSS/P3HT:PC60BM/LiF/Al. We find that in the case of the small molecule based OSC diffusion dominates over recombination for this thickness, L=125 nm, even at high frequencies. We calculate the effective carrier lifetimes and mobilities for both structures using both models. Average electron mobility calculated for the small molecule cell is around 4–6.4×10−3 cm2/Vs, slightly higher than that obtained for the standard blend which is around 2×10−3 cm2/Vs.

We report on the fabrication of Indium Tin Oxide (ITO)-free inverted organic bulk heterojunction (BHJ) photodetectors of poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)propyl-1-1-phenyl-(6,6) C61 (PCBM). The final inverted device structure is Cr/Al/Cr/P3HT:PCBM/poly-3,4-ethylenedioxythiophene:poly-styrenesulfonate (PEDOT:PSS)/Ag (Zimmermann et al., 2009) [1]. The device is top-absorbing with the light entering through the hole contact grid. We have fabricated standard devices with structure ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al in order to carry out a comparison study. Inverted photodetectors show slightly higher quantum efficiency and responsivity compared to standard devices. Frequency responses at different bias voltages were measured showing a maximum -3 dB cut-off frequency of 780 kHz and 700 kHz at -3 V for the standard and inverted structures respectively. Parameters extracted from the fit of a circuital model to the impedance spectroscopy measurements were used to estimate the photodiode cut-off frequency as function of bias. (C) 2013 Elsevier B.V. All rights reserved. Tecnología Electrónica

The fraction of β chains is expected to have a strong influence on the energy transfer processes in organic light-emitting diodes based on mixed phase polyfluorene doped with transition metal phosphors. Here, we report on the electroluminescence emission properties of devices based on poly(9,9-dioctylfluorene), containing different fractions of β phase, doped with varying ratios of an iridium triplet emitter. We measure the electroluminescence spectra at constant current density and the current density–voltage characteristics of the diodes. We also investigate the temperature dependence of electroluminescence emission within a temperature range between 77 and 270 K in this system. For a given dopant concentration and β phase content, the electroluminescent emission covers a broad range of the spectrum. Trap-assisted recombination in β phase sites, which act as electron trapping sites, would compete with direct charge recombination in dopant sites, which might act as a hole trap. Singlet energy transfer se...

In this work we have fabricated passive diode matrices based on a new blue emitting organic electroluminescent polymer. In order to determine the capacitive response at typical display operating frequencies, impedance vs frequency measurements have been carried out at different bias. In addition, hole mobilities have been extracted by fitting a new theoretical model to the measured admittance, that takes into account the effect of an injection barrier, obtaining values from 10−12 m2/Vs to 10−10 m2/Vs with increasing bias.

The CD73 ectonucleotidase catalyses the hydrolysis of AMP to adenosine, an immunosuppressive molecule. Recent evidence has demonstrated that this ectonucleotidase is up-regulated in T helper type 17 cells when generated in the presence of transforming growth factor-β (TGF-β), and hence CD73 expression is related to the acquisition of immunosuppressive potential by these cells. TGF-β is also able to induce CD73 expression in CD8(+) T cells but the function of this ectonucleotidase in CD8(+) T cells is still unknown. Here, we show that Tc17 cells present high levels of the CD73 ectonucleotidase and produce adenosine; however, they do not suppress the proliferation of CD4(+) T cells. Interestingly, we report that adenosine signalling through A2A receptor favours interleukin-17 production and the expression of stem cell-associated transcription factors such as tcf-7 and lef-1 but restrains the acquisition of Tc1-related effector molecules such as interferon-γ and Granzyme B by Tc17 cells. Within the tumour microenvironment, CD73 is highly expressed in CD62L(+) CD127(+) CD8(+) T cells (memory T cells) and is down-regulated in GZMB(+) KLRG1(+) CD8(+) T cells (terminally differentiated T cells), demonstrating that CD73 is expressed in memory/naive cells and is down-regulated during differentiation. These data reveal a novel function of CD73 ectonucleotidase in arresting CD8(+) T-cell differentiation and support the idea that CD73-driven adenosine production by Tc17 cells may promote stem cell-like properties in Tc17 cells.

In this work, conditions of Suzuki condensation and polymer modification of polymers of benzene and fluorene units have been studied. A new polymer was prepared with statistical equimolecular amounts of two 2,7-dibromo-9,9-bis(6‘-susbtituted-hexyl)fluorene as starting monomers. The C9 position of the poly[9,9-bis(6‘-bromohexylfluoren-2,7-diyl)-alt-co-(benzen-1,4-diyl has been substituted yielding poly[9,9-bis(6‘-cyanohexylfluoren-2,7-diyl)-alt-co-(benzen-1,4-diyl)] with a high degree of conversion. All polymers were completely soluble in THF and chloroform and were characterized by NMR, FTIR, and elemental analysis. Molecular weights measured by gel permeation chromatography coupled with light scattering detector results in polydispersity values between 3.3 and 1.2. Their glass transitions temperature were over 90 and 99 °C by DSC. Comparative studies of optical properties in solution and solid state show similar values indicating that the remote substitution of functional group maintains the spectroscopi...

OBJECTIVE To compare the prevalence of diabetic retinopathy (DR) between low-income Mexicans from Mexico City and Mexican-Americans from San Antonio, Texas. RESEARCH DESIGN AND METHODS We designed a cross-sectional population-based study in low-income neighborhoods of Mexico City and San Antonio. The men and non-pregnant women included in the study had NIDDM and were between 35 and 64 years of age. Ophthalmologic evaluation was performed in 414 patients, 204 in San Antonio and 210 in Mexico City. Seven field standard stereophotographs of each eye were obtained, adapting the Early Treatment Diabetic Retinopathy Study protocol, and graded at the Fundus Photograph Reading Center of the University of Wisconsin. RESULTS Early nonproliferative DR occurred in 37 (17.6%) and 39 (19.1%) patients in Mexico City and San Antonio, respectively. Moderate-to-severe nonproliferative DR occurred in 55 (26.2%) and 37 (18.1%) patients in Mexico City and San Antonio, respectively, and proliferative DR occurred in 12 (5.7%) and 7 (3.4%) patients in Mexico City and San Antonio, respectively. Using univariate and multivariate logistic regression analysis with DR as the dependent variable, age, duration of disease, and fasting glucose concentration were positively and significantly associated with retinopathy, whereas city, systolic blood pressure, and other selected metabolic variables were not. We defined moderate-to-severe DR to include the categories of moderate-to-severe nonproliferative and proliferative DR. For this combined category, Mexico City patients with diabetes had a significantly higher prevalence (P < 0.01) than those from San Antonio when analyzed by multiple logistic regression analysis (odds ratio for Mexico City/San Antonio, 1.72; 95% CI 1.10–2.70). CONCLUSIONS Overall prevalence of DR is similar in both cities. However, moderate-to-severe DR is significantly higher in Mexico City.

Organic bulk heterojunction photodiodes based on a blend of poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6, 6)C61 (P3HT:PCBM) have been fabricated with different active layer thicknesses. Current-voltage characteristics and cut-off frequency were measured under Green-LED illumination. Impedance measurements were performed and a simple equivalent circuit was used to fit the resulting Cole-cole diagram. Parameters obtained from the fit were used to estimate the theoretical photodetector cut-off frequency and compared to the experimental one. The material dielectric constant was estimated using the capacitance obtained from the impedance fit.

In this work we have fabricated and characterized organic solar cells (OSC) based on blends of polyhexylthiophene (P3HT) and [6,6]-phenil-C61-butyric acid methyl ester (PCBM) with two different cathodes: Al and LiF/Al. Current- Voltage (I-V) curves under illumination have been measured and fitted with the standard equivalent circuit in order to extract circuital parameters, such as series and parallel resistances (Rs and Rp) ideality factor (n) and inverse saturation current (I0). The introduction of a thin layer (0.5 nm) of LiF between active layer and Al increases the open circuit voltage (Voc) but slightly reduces short current (Isc) and fill factor (FF). The overall result is a slight increase of the efficiency, from 2.53 % to 2.57 %. Circuital parameters have been extracted with two methods (approximated an exact), and results show that structures with LiF layer have lower parasitic effects (lower Rs and higher Rp).

In this work we use a modified equivalent circuit to simulate the S-shape found in current density–voltage ( J – V ) characteristics of organic solar cells (OSC) based on P3HT:PCBM. The modification of the traditional model includes a second diode opposite to the main one together with a parallel resistance, R P 2 . The transcendental equation derived from the circuit is solved exactly without approximations. The S-shape (so called kink), usually attributed to a poor quality of polymer/cathode interface, can be removed after three slow annealing treatments. The evolution of the J – V curves with the annealing process has been quantified by extracting the equivalent circuit parameters of each curve (pristine and annealed) by fitting the model to the experimental data. Results show that kink annihilation is mostly due to a strong decrease of R P 2 , which diminishes the reverse diode effect on the J – V curve.

An organic bulk heterojunction photodetector (OPD) is fabricated on the basis of a blend of poly(3-hexyl thiophene):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61. The OPD responsivity is calculated from current density-voltage characteristic (J-V) under green-LED illumination obtaining 1 A/W. Frequency response at different biases is measured, which shows a high ¿3-dB cutoff frequency of 343 kHz at ¿3 V. Impedance measurements are carried out at different reverse biases, and the results are fitted with a small signal equivalent circuit. The device cutoff frequency (fc) can be estimated with the parameters extracted from this circuit obtaining good agreement between measured and calculated fc. Tecnología Electrónica

he electrical behavior of organic solar cell (OSC) has been analyzed using a simple circuital model consisting on an ideal diode together with a series and parallel resistances (R-S and R-P respectively). Applying Kirchhoff's Laws to the circuit leads to a transcendental equation that can be solved numerically without approximations using the Lambert W function. Theoretical expression has been fitted to experimental current-voltage (I-V) curves under forward bias, obtaining fairly accurate values for the electrical parameters. This model has been validated comparing the extracted parameters for dark and illumination conditions of different devices. Results show good agreement for R-S, and ideality factor eta. Electrical parameters obtained in this work are also compared to those ones extracted using an approximated method often employed by other authors (1). We conclude that approximated method leads to reasonable good values for R-S, R-P and. However, in the case of Rp the voltage range chosen to fit the data with the exact method must be constrained to the fourth quadrant, where the role of parallel resistance is more critical. To validate the model, a bunch of organic solar cells with structure ITO/ poly(3,4-ethylenedioxythiophene)-poly (4-styrene sulfonate (PEDOT:PSS)/ poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (PCBM)/Al has been fabricated in inert atmosphere. Different active layers were deposited varying the P3HT: PCBM ratio (1:0.64, 1:1, 1:1.55) and the active layer thickness ( ranging from 100 to 280 nm). Devices are encapsulated inside the glove-box prior its characterization outside the glove-box. Electro optical characterization has been performed with a halogen lamp. Values extracted for RS range from 142 Omega to 273 Omega, values for R-P range from 25 k Omega to 331 k Omega. Ideality factor ranges from 5 to 17. Tecnología Electrónica

Organic solar cells (OSCs) often show a kink, also called S-shape, in the current–voltage (I–V) characteristics, that has been attributed to different physical phenomena such as poor quality of cathode-active layer interface or unbalance charge carrier mobilities. This nonideal behaviour can be electrically modelled including a second diode, in reverse bias, together with an extra shunt resistance (RP2) in the traditional solar cell equivalent circuit. In this paper, we solve without approximations the transcendental equation system derived from this modified circuit. We have obtained an analytical expression for I–V curves decoupling the voltage drop in each diode using Lambert W function. This expression has been fitted to experimental data in order to obtain circuital parameters. Simulations varying saturation current of reverse diode (I02) and RP2 have been performed in order to study the dependence of S-shape with these parameters. 2012 Elsevier Ltd. All rights reserved.

In this work we report a detailed comparison of optical and electrical degradation between alpha- and beta-phase poly(9,9-dioctyfluorene) (PFO) based diodes. Analysis of the EL spectra along continuous operation time in alpha- and beta-PFO based diodes reveals that the unwanted green emission traditionally associated to fluorenone is more likely to occur in a-phase PFO. The relative spectral areas arising from excitonic and vibronic transitions as well as fluorenone defects have been quantified by means of Gaussian deconvolution along the operation time. The relative spectral area associated to the formation of the fluorenone increases 13% for the beta-PFO diode and up to 21% for the alpha-PFO diode only after 35 min of continuous operation. Analysis of the I-V curve before and after electrical stressing has lead to hole mobilities in pristine diodes of 1.4 x 10(-4) cm(2)/Vs and 1.6 x 10(-5) cm(2)/Vs for beta-PFO and alpha-PFO respectively. Both beta-PFO and alpha-PFO degraded samples show a reduction in the hole mobility, as well as an increase in the width of the Gaussian density of states. Tecnología Electrónica

Article of the IEEE Education Engineering Conference (EDUCON). Keywords: educational courses, electronic engineering education, telecommunication engineering education, electronics curriculum, project based learning activities, project-oriented integral curriculum, telecommunication engineer degree, university degree structure, Bologna process This paper describes the Electronics curriculum in the Telecommunication Engineer degree at Rey Juan Carlos University (URJC) in Spain. Telecommunication Engineering started in the 2003-2004 academic year. In these years, all the electronic courses have been set up with a main practical orientation and with Project Based Learning (PBL) activities, both compulsory and voluntary. Once these courses have been successfully implemented we have reoriented some of the practical activities to be more interlaced. In this sense, projects involving students of different courses have been developed, as well as projects involving students from different years. All these activities fit in the principles promulgated by the Declaration of Bologna, which results in the actual updating of the university degree structure in Spain. Tecnología Electrónica

In this paper we propose a model to simulate electrical conduction of single carrier organic diodes in the presence of a barrier for carrier injection, and considering a field-dependent carrier mobility. An analytical expression for the internal electric field function, that simplifies operation with the resulting non-linear equation system, is provided. The results of the model are compared with those from other existing approaches that assume simplifications. Finally, the current density versus voltage curves predicted by this model for diodes with different active layer thicknesses show a good agreement with the experimental results.

PEDOT [Poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate)] is a material typically used organic light emission displays (OLEDs) manufactured as a conductor, or rather, as a hole injector. In this paper, three different issues have been studied: the use of rubbed PEDOT as alignment layer, the resistivity of the applied PEDOT layers, i.e., its potential as a replacement of ITO electrodes, and the induction of asymmetry in the electro-optical response of liquid crystal cells by assembling the display with dissimilar coated aligning surfaces — PEDOT on one side and buffed nylon on the counter electrode

An analytical, complete framework to describe the current-voltage (I-V) characteristics of organic diodes without the use of previous approaches, such as injection or bulk-limited conduction is proposed. Analytical expressions to quantify the ratio between injection and space-charge-limited current from experimental I-V characteristics in organic diodes have been derived. These are used to propose a numerical model in which both bulk transport and injection mechanisms are considered simultaneously. This procedure leads to a significant reduction in computing time with respect to previous rigorous numerical models. In order to test the model, different diode structures based on two different polymers: poly(2-methoxy-5-{3',7'-dimethyloetyloxy}-p-phenylenevinylene) (MDMO-PPV) and a derivative of the poly(2,7-fluorene phenylidene) [PFP:(CN)(2)], have been fabricated. The present model is excellently fitted to experimental curves and yields the microscopic parameters that characterize the active layer. Tecnología Electrónica

Common cathode organic electroluminescent diode matrices, based on a new CN-derivative of poly(2,7-fluorene phenylidene) have been developed by photolithography. Optical characterization reveals their interesting properties as white-light emitters. In addition, 7times5 pixel alphanumeric display prototypes have been manufactured using a novel lithographic technique that saves processing steps and costs.