Regenerated Cellulose Fiber Solar Cell

Wearable electronics and smart textiles are growing fields in the cause to integrate modern communication and computing tools into clothing instead of carrying around smart phones and tablets. Naturally, this also requires power sources to be integrated in textiles. In this paper, a proof-of-concept is presented in form of a photovoltaic cell based on a commercially available viscose fiber. This has been realized using a silver nanowire network around the viscose fiber to establish electrical contact and a photoactive coating using the standard workhorse among organic thin film solar cells, a blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Structure and performance of single fiber devices demonstrate their feasibility and functionality. The applied materials and methods are compatible to solution processing therewith qualifying for potential roll-to-roll large-scale production

Short-Term Environmental Effects and Their Influence on Spatial Homogeneity of Organic Solar Cell Functionality

In this study, we focus on the induced degradation and spatial inhomogeneity of organic photovoltaic devices under different environmental conditions, uncoupled from the influence of any auxiliary hole-transport (HT) layer. During testing of the corresponding devices comprising the standard photoactive layer of poly­(3-hexylthiophene) as donor, blended with phenyl-C₆₁-butyric acid methyl ester as acceptor, a comparison was made between the nonencapsulated devices upon exposure to argon in the dark, dry air in the dark, dry air with illumination, and humid air in the dark. The impact on the active layer’s photophysics is discussed, along with the device physics in terms of integral solar cell performance and spatially resolved photocurrent distribution with point-to-point analysis of the diode characteristics to determine the origin of the observed integrated organic photovoltaic device behavior. The results show that even without the widely used hygroscopic HT layer, poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate), humidity is still a major factor in the short-term environmental degradation of organic solar cells with this architecture, and not only oxygen or light, as is often reported. Different from previous reports where water-induced device degradation was spatially homogeneous and formation of Al₂O₃ islands was only seen for oxygen permeation through pinholes in aluminum, we observed insulating islands merely after humidity exposure in the present study. Further, we demonstrated with laser beam induced current mapping and point-to-point diode analysis that the water-induced performance losses are a result of the exposed device area comprising regions with entirely unaltered high output and intact diode behavior and those with severe degradation showing detrimentally lowered output and voltage-independent charge blocking, which is essentially insulating behavior. It is suggested that this is caused by transport of water through pinholes to the organic/metal interface, where they form insulating oxide or hydroxide islands, while the organic active layer stays unharmed

Phosphorylation of Phenol by Phenylphosphate Synthase: Role of Histidine Phosphate in Catalysis

The anaerobic metabolism of phenol proceeds via carboxylation to 4-hydroxybenzoate by a two-step process involving seven proteins and two enzymes (“biological Kolbe-Schmitt carboxylation”). MgATP-dependent phosphorylation of phenol catalyzed by phenylphosphate synthase is followed by phenylphosphate carboxylation. Phenylphosphate synthase shows similarities to phosphoenolpyruvate (PEP) synthase and was studied for the bacterium Thauera aromatica. It consists of three proteins and transfers the β-phosphoryl from ATP to phenol; the products are phenylphosphate, AMP, and phosphate. We showed that protein 1 becomes phosphorylated in the course of the reaction cycle by [β-(32)P]ATP. This reaction requires protein 2 and is severalfold stimulated by protein 3. Stimulation of the reaction by 1 M sucrose is probably due to stabilization of the protein(s). Phosphorylated protein 1 transfers the phosphoryl group to phenolic substrates. The primary structure of protein 1 was analyzed by nanoelectrospray mass spectrometry after CNBr cleavage, trypsin digestion, and online high-pressure liquid chromatography at alkaline pH. His-569 was identified as the phosphorylated amino acid. We propose a catalytic ping-pong mechanism similar to that of PEP synthase. First, a diphosphoryl group is transferred to His-569 in protein 1, from which phosphate is cleaved to render the reaction unidirectional. Histidine phosphate subsequently serves as the actual phosphorylation agent

Influence of environmentally affected hole-transport layers on spatial homogeneity and charge-transport dynamics of organic solar cells

After the efficiency of organic photovoltaic (OPV) cells achieved more than 10%, the control of stability and degradation mechanisms of solar cells became a prominent task. The improvement of device efficiency due to incorporation of a hole-transport layer (HTL) in bulk-heterojunction solar cells has been extensively reported. However, the most widely used HTL material, PEDOT:PSS is frequently suspected to be the dominating source for devices instability under environmental conditions. Thereby effects like photooxidation and electrode corrosion are often reported to shorten device lifetime. However, often in environmental device studies, the source of degradation, whether being from the HTL, the active layer or the metal cathode are rather difficult to distinguish, because the external diffusion of oxygen and water affects all components. In this study, different HTLs, namely prepared from traditional PEDOT:PSS and also two types of molybdenum trioxide (MoO3), are exposed to different environments such as oxygen, light or humidity, prior to device finalization under inert conditions. This allows investigating any effects within the HTL and from reactions at its interface to the indium-tin-oxide electrode or the active layer. The surface and bulk chemistry of the exposed HTL has been monitored and discussed in context to the observed device physics, dynamic charge transport and spatial performance homogeneity of the according OPV device. The results show that merely humidity-exposure of the HTL leads to decreased device performance for PEDOT:PSS, but also for one type of the tested MoO3. The losses are related to the amount of absorbed water in the HTL, inducing loss of active area in terms of interfacial contact. The device with PEDOT:PSS HTL after humid air exposure showed seriously decreased photocurrent by micro-delamination of swelling/shrinkage of the hygroscopic layer

Characterization of surface and structure of in situ doped sol‐gel‐derived silicon carbide

Silicon carbide (SiC), is an artificial semiconductor used for high-power transistors and blue LEDs, for its extraordinary properties. SiC would be attractive for more applications, but large-scale or large-surface area fabrication, with control over defects and surface is challenging. Sol-gel based techniques are an affordable alternative towards such requirements. This report describes two types of microcrystalline SiC derived after carbothermal reduction from sol-gel-based precursors, one with nitrogen added, the other aluminum. Characterization of their bulk, structure and surface shows that incorporation of dopants affects the formation of polytypes and surface chemistry. Nitrogen leads exclusively to cubic SiC, exhibiting a native oxide surface. Presence of aluminum instead promotes growth of hexagonal polytypes and induces self-passivation of the crystallites surface during growth. This is established by hydrogenation of silicon bonds and formation of a protecting aluminum carbonate species. XPS provides support for the suggested mechanism. This passivation is achieved in only one step, solely by aluminium in the precursor. Hence, it is shown that growth, doping and passivation of SiC can be performed as one-pot synthesis. Material without insulating oxide and a limited number of defects is highly valuable for applications involving surface-sensitive charge-transfer reactions, therefore the potential of this method is significant

Interfacial Morphology and Effects on Device Performance of Organic Bilayer Heterojunction Solar Cells

The effects of interface roughness between donor and acceptor in a bilayer heterojunction solar cell were investigated on a polymer–polymer system based on poly­(3-hexylthiophene) (P3HT) and poly­(dioctylfluorene-<i>alt</i>-benzothiadiazole) (F8BT). Both polymers are known to reorganize into semicrystalline structures when heated above their glass-transition temperature. Here, the bilayers were thermally annealed below glass transition of the bulk polymers (≈140 °C) at temperatures of 90, 100, and 110 °C for time periods from 2 min up to 250 min. No change of crystallinity could be observed at those temperatures. However, X-ray reflectivity and device characteristics reveal a coherent trend upon heat treatment. In X-ray reflectivity investigations, an increasing interface roughness between the two polymers is observed as a function of temperature and annealing time, up to a value of 1 nm. Simultaneously, according bilayer devices show an up to 80% increase of power conversion efficiency (PCE) for short annealing periods at any of the mentioned temperatures. Together, this is in agreement with the expectations for enlargement of the interfacial area. However, for longer annealing times, a decrease of PCE is observed, despite the ongoing increase of interface roughness. The onset of decreasing PCE shifts to shorter durations the higher the annealing temperature. Both, X-ray reflectivity and device characteristics display a significant change at temperatures below the glass transition temperatures of P3HT and F8BT