Fabricating high performance conventional and inverted polymer solar cells by spray coating in air

We report bulk heterojunction organic solar cells utilising the electron-donating polymer PffBT4T-2OD blended with the fullerene acceptor PC71BM, with cells explored based on both conventional and inverted architectures. As charge-transporting layers, we utilise the hole-transporting polymer poly (2, 3-dihydrothieno-1, 4-dioxin)-poly (styrenesulfonate) (PEDOT:PSS) in conventional device architectures, and zinc oxide (ZnO) electron-transport in inverted devices. Critically, all charge-transporting layers and the poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt- (3,3‴-di(2-octyldodecyl) 2,2'; 5',2''; 5″,2‴ -quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) active layer blend were spray coated in air. We demonstrate champion devices having a power conversion efficiency of 8.13% and 8.43% for conventional and inverted architectures respectively

High efficiency arrays of polymer solar cells fabricated by spray-coating in air

We present bulk heterojunction organic solar cells fabricated by spray-casting both the PEDOT:PSS hole-transport layer (HTL) and active PBDTTT-EFT:PC71BM layers in air. Devices were fabricated in a (6 × 6) array across a large-area substrate (25 cm2) with each pixel having an active area of 6.45 mm2. We show that the film uniformity and operational homogeneity of the devices are excellent. The champion device with spray cast active layer on spin cast PEDOT:PSS had an power conversion efficiency (PCE) of 8.75%, and the best device with spray cast active layer and PEDOT:PSS had a PCE of 8.06%. The impacts of air and light exposure of the active layer on device performance are investigated and found to be detrimental

Polymer-based solar cells having an active area of 1.6 cm2 fabricated via spray coating

We demonstrate the fabrication of polymersolar cells in which both a PEDOT:PSS hole transport and a PCDTBT:PC71BM photoactive layer are deposited by spray-casting. Two device geometries are explored, with devices having a pixel area of 165 mm2 attaining a power conversion efficiency of 3.7%. Surface metrology indicates that the PEDOT:PSS and PCDTBT:PC71BM layers have a roughness of 2.57 nm and 1.18 nm over an area of 100 μm2. Light beam induced current mapping reveals fluctuations in current generation efficiency over length-scales of ∼2 mm, with the average photocurrent being 75% of its maximum value

Organic photovoltaic devices with enhanced efficiency processed from non-halogenated binary solvent blends

The development of processing routes to fabricate organic photovoltaic devices (OPVs) using non-halogenated solvents is a necessary step towards their eventual commercialisation. To address this issue, we have used Hansen solubility parameter analysis to identify a non-halogenated solvent blend based on a mixture of carbon disulphide and acetone. This solvent blend was then used to deposit a donor–acceptor polymer–fullerene thin-film that was then used as the active layer of bulk-heterojunction OPV. For the benchmark polymer:fullerene system PCDTBT:PC70BM, a power conversion efficiency of 6.75% was achieved; a 20% relative improvement over reference cells processed using the chlorinated-solvent chlorobenzene. Improvements in device efficiency are attributed to an increase in electron and hole conductivity resulting from enhanced fullerene crystallisation; a property that leads to enhanced device efficiency through improved charge extraction

The effect of residual palladium catalyst on the performance and stability of PCDTBT:PC70BM organic solar cells

Palladium (Pd) is commonly used as a catalyst in the polymerisation of conjugated polymers such as poly[N-9′-heptadecanyl-2,7-carbozole-alt-5,5-(4′,7′-di-2-thenyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). Here we explore the effect of residual catalyst on the performance of organic photovoltaic devices (OPVs) based on a PCDTBT:fullerene thin-film blend. We find that as the relative concentration of Pd increases, the power conversion efficiency of the PV is reduced, dropping from 4.55% to 2.42% as the Pd concentration was increased to 2570 ppm (relative to that of the PCDTBT). This reduction in efficiency resulted primarily from a reduction in PV fill factor and shunt-resistance, indicating the presence of current-shunts within the device. Using optical microscopy, laser beam induced current mapping and scanning electron microscopy, we are able to demonstrate that such current shunts are associated with micron-sized aggregates of Pd-containing nanoparticles. We show that the presence of high concentrations of Pd within a PCDTBT OPV contribute to a larger drop in efficiency during the initial ‘burn-in’ period

Polioencefalomalacia em bovinos nos estados de Mato Grosso do Sul e São Paulo Polioencephalomalacia in cattle in the states of Mato Grosso do Sul and São Paulo

Trinta focos de polioencefalomalacia (PEM) foram diagnosticados no período de agosto de 1993 a outubro de 1997. Vinte e nove focos ocorreram no estado de Mato Grosso do Sul (MS) e um no estado de São Paulo (SP). Foram afetados bovinos de 4 a 84 meses de idade. A morbidade dos rebanhos afetados variou de 0,02% a 14,28% e a letalidade de 42,5% a 100%. A doença não apresentou uma sazonalidade e ocorreu em vários municípios do MS. Em todos os focos estudados os animais afetados eram criados em regimes de criação extensiva, com exceção de um foco. Os sinais clínicos observados foram exclusivamente nervosos e a evolução dos casos variou de 12 horas a 4 dias. A maioria dos animais tratados com tiamina e dexametasona recuperou-se. Histologicamente, as lesões consistiam de necrose laminar do córtex cerebral. Adicionalmente em 2 casos observaram-se hemorragias submeningeanas e corticais, e em 9 casos presença de infiltrado de eosinófilos. A dosagem de sódio no líquor apresentou-se elevada em um caso. A etiologia da PEM não está esclarecida, porém em alguns casos a intoxicação por cloreto de sódio/privação de água pode estar envolvida na etiologia da enfermidade. A PEM representa 4,78% dos casos de enfermidades de bovinos diagnosticadas no Laboratório de Anatomia Patológica da UFMS. Com bases nos resultados, verifica-se a importância da enfermidade no diagnóstico diferencial de outras doenças com quadro clínico neurológico no MS, principalmente a raiva, a meningoencefalite por herpesvírus bovino tipo 5 (HVB-5) e o botulismo.<br>Thirty outbreaks of polioencephalomalacia (PEM) were diagnosed from August 1993 to October 1997. Twenty nine occurred in the state of Mato Grosso do Sul and one in São Paulo. The disease affected cattle from 4 months to 7 years of age. Morbidity rates ranged from 0.02% to 14.28% and case fatalities from 42.5 % to 100%. The disease was not seasonal. All outbreaks occurred in cattle grazing Brachiaria spp, except one affecting feedlot cattle. Only neurologic signs were observed, and the course of the disease varied from 12 hours to 4 days in untreated cattle. Most animals treated with thiamine and dexamethazone recovered. Moderate cerebral edema was observed at necropsy. Cell changes were characterized by laminar necrosis and gitter cells. In two cases moderate cortical and submeningeal hemorrhages were observed. Nine cases had perivascular and submeningeal infiltrations by eosinophils. Sodium ion concentration of the cerebrospinal fluid was elevated in one case. The cause of PEM in the region was not determined, but the results suggest that in some cases sodium chloride intoxication/water deprivation could play a role in the etiology of the disease. PEM represents 4.78% of cattle disease diagnosed at the Pathology Laboratory of the Federal University of Mato Grosso do Sul