The Influence of Conjugated Polymer Side Chain Manipulation on the Efficiency and Stability of Polymer Solar Cells.

The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole (TzTz) acceptor units, were selected toward effective device scalability by roll-coating. The influence of the partial exchange (5% or 10%) of the solubilizing 2-hexyldecyloxy by alternative 2-phenylethoxy groups on efficiency and stability was investigated. With an increasing 2-phenylethoxy ratio, a decrease in solar cell efficiency was observed for the BT-based series, whereas the efficiencies for the devices based on the TzTz polymers remained approximately the same. The photochemical degradation rate for PSCs based on the TzTz polymers decreased with an increasing 2-phenylethoxy ratio. Lifetime studies under constant sun irradiance showed a diminishing initial degradation rate for the BT-based devices upon including the alternative side chains, whereas the (more stable) TzTz-based devices degraded at a faster rate from the start of the experiment upon partly exchanging the side chains. No clear trends in the degradation behavior, linked to the copolymer structural changes, could be established at this point, evidencing the complex interplay of events determining PSCs' lifetime.

On the stability of a variety of organic photovoltaic devices by IPCE and in situ IPCE analyses--the ISOS-3 inter-laboratory collaboration.

This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RISØ-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N(2)) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO(3)), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime.

TOF-SIMS investigation of degradation pathways occurring in a variety of organic photovoltaic devices--the ISOS-3 inter-laboratory collaboration.

The present work is the fourth (and final) contribution to an inter-laboratory collaboration that was planned at the 3rd International Summit on Organic Photovoltaic Stability (ISOS-3). The collaboration involved six laboratories capable of producing seven distinct sets of OPV devices that were degraded under well-defined conditions in accordance with the ISOS-3 protocols. The degradation experiments lasted up to 1830 hours and involved more than 300 cells on more than 100 devices. The devices were analyzed and characterized at different points of their lifetimes by a large number of non-destructive and destructive techniques in order to identify specific degradation mechanisms responsible for the deterioration of the photovoltaic response. Work presented herein involves time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to study chemical degradation in-plane as well as in-depth in the organic solar cells. Various degradation mechanisms were investigated and correlated with cell performance. For example, photo-oxidation of the active material was quantitatively studied as a function of cell performance. The large variety of cell architectures used (some with and some without encapsulation) enabled valuable comparisons and important conclusions to be drawn on degradation behaviour. This comprehensive investigation of OPV stability has significantly advanced the understanding of degradation behaviour in OPV devices, which is an important step towards large scale application of organic solar cells.

Effects of cannabinoid CB1 receptor agonism and antagonism on SKF81297-induced dyskinesia and haloperidol-induced dystonia in Cebus apella monkeys.

Antipsychotic drugs may cause extrapyramidal symptoms (EPS), such as dyskinesia and dystonia. These effects are believed to involve dysfunctional striatal dopamine transmission. Patients with schizophrenia show increased prevalence of cannabis abuse and this has been linked to severity of EPS. Endocannabinoids modulate striatal dopamine activity via type 1 cannabinoid (CB(1)) receptors, and studies in rats and humans suggest beneficial effects of CB(1) ligands on EPS. The present study explored the effects of CB(1) receptor ligands on oral dyskinesia induced by the dopamine D(1) receptor agonist SKF81297 (SKF) and acute dystonia induced by the dopamine D(2) receptor antagonist haloperidol in Cebus apella monkeys. The monkeys were sensitised to EPS by prior exposure to D(2) receptor antagonists. SKF (0.3 mg/kg) was administered alone and in combination with the CB(1) agonist CP55,940 (0.0025-0.01 mg/kg) or the CB(1) antagonist SR141716A (0.25-0.75 mg/kg). Haloperidol (individual doses at 0.01-0.02 mg/kg) was administered alone and in combination with CP55,940 (0.005 or 0.01 mg/kg) or SR141716A (0.5 or 0.75 mg/kg). Subsequently, the monkeys were videotaped, and the recordings were rated for oral dyskinesia or dystonia. SKF-induced oral dyskinesia was dose-dependently reduced by CP55,940, with no effect of SR141716A. Haloperidol-induced dystonia was not affected by either CP55,940 or SR141716A.

Degradation patterns in water and oxygen of an inverted polymer solar cell.

The spatial distribution of reaction products in multilayer polymer solar cells induced by water and oxygen atmospheres was mapped and used to elucidate the degradation patterns and failure mechanisms in an inverted polymer solar cell. The active material comprised a bulk heterojunction formed by poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) sandwiched between a layer of zinc oxide and a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) that acted as, respectively, electron and hole transporting layers between the active material and the two electrodes indium-tin-oxide (ITO) and printed silver. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) in conjunction with isotopic labeling using H(2)(18)O and (18)O(2) enabled detailed information on where and to what extent uptake took place. A comparison was made between the use of a humid (oxygen-free) atmosphere and a dry oxygen atmosphere during testing of devices that were kept in the dark and devices that were subjected to illumination under simulated sunlight. It was found that the reactions taking place at the interface between the active layer and the PEDOT:PSS were the major cause of device failure in the case of these inverted devices, which are compatible with full roll-to-roll (R2R) coating and industrial manufacture. The PEDOT:PSS was found to phase separate, with the PEDOT-rich phase being responsible for most of the interface degradation in oxygen atmospheres. In water atmospheres, little chemically induced degradation was observed, whereas a large partially reversible dependence of the open circuit voltage on the relative humidity was observed. In addition, temporal aspects are discussed in regard to degradation mechanisms. Finally, analytical aspects in regard to storing devices are discussed.

Effects of the cannabinoid CB1 receptor agonist CP55,940 and antagonist SR141716A on d-amphetamine-induced behaviours in Cebus monkeys.

Several clinical studies have shown that alterations in the cannabinoid system in the brain may be associated with schizophrenia. Although evidence points towards an antipsychotic potential for cannabinoid antagonists, experimental studies have shown inconsistent behavioural effects of cannabinoid ligands within and across species. The aim of the present study was to explore these contradictory findings in a non-human primate model, predictive of antipsychotic efficacy in humans. The effects of the cannabinoid CB1 receptor antagonist SR141716A and the CB1 receptor agonist CP55,940 were explored in an d-amphetamine-based Cebus monkey model of psychosis. The monkeys were sensitive to extrapyramidal side effects (EPS), and the side-effect profiles of the drugs were explored as well. SR141716A (0.1, 0.25, 0.375, 0.5 and 0.75 mg/kg) and CP55,940 (0.0025, 0.005 and 0.01 mg/kg) were administered by subcutaneous injection alone and in combination with d-amphetamine (0.25mg/kg). SR141716A (0.1-0.5mg/kg) reduced d-amphetamine-induced arousal, while CP55,940 had no significant effect upon d-amphetamine-induced behaviours. No EPS were observed with either of these compounds. These data suggest that cannabinoid CB1 antagonists such as SR141716A may have limited antipsychotic potential in man as to positive symptoms. SR141716A administered alone induced anxiolytic-like behaviour, whereas administration of CP55,940 alone showed anxiogenic properties.