Near-field scanning photocurrent microscopy (NSPM) measurements probing the relationship between morphology and current generation in photovoltaic devices based on p-xylene processed poly(9,9′-dioctylfluorene-co-bis-N,N′-(4,butylphenyl)-bis-N,N′-phenyl-1,4-phenylene-diamine)[PFB] and poly(9,9′-dioctylfluorene-co-benzo-thiadiazole) [F8BT] blend films are presented. We find that current generation occurs primarily from within the micron-sized phase-segregated domains, with the PFB-rich phase contributing significantly more current than the surrounding F8BT-rich regions. These results are explained by nanoscale intermixing within the micron-sized domains, with differing extents of intermixing in the PFB-and F8BT-rich domains.

Direct photocurrent mapping of organic solar cells (OSCs) using a novel implementation of a near-field scanning optical microscope (NSOM) is described. By rastering the light output from the NSOM through a semitransparent electrode across the OSC surface, it is possible to collect height and photocurrent images simultaneously with a lateral resolution that is governed by the NSOM aperture. The photocurrent images demonstrate that film inhomogeneities and segregation effects strongly influence OSC device performance.

1. Mechanisms underlying the generation and propagation of gastrointestinal slow wave depolarizations have long been controversial. The present review aims to collate present knowledge on this subject with specific reference to slow waves in gastric smooth muscle. 2. At present, there is strong agreement that interstitial cells of Cajal (ICC) are the pacemaker cells that generate slow waves. What has been less clear is the relative role of primary types of ICC, including the network in the myenteric plexus (ICC-MY) and the intramuscular network (ICC-IM). It is concluded that both ICC-MY and ICC-IM are likely to serve a major role in slow wave generation and propagation. 3. There has been long-standing controversy as to how slow waves 'propagate' circumferentially and down the gastrointestinal tract. Two mechanisms have been proposed, one being action potential (AP)-like conduction and the other phase wave-based 'propagation' resulting from an interaction of coupled oscillators. Studies made on single bundle gastric strips indicate that both mechanisms apply with relative dominance depending on conditions; the phase wave mechanism is dominant under circumstances of rhythmically generating slow waves and the AP-like propagation is dominant when the system is perturbed. 4. The phase wave mechanism (termed Ca(2+) phase wave) uses cyclical Ca(2+) release as the oscillator, with coupling between oscillators mediated by several factors, including: (i) store-induced depolarization; (ii) resultant electrical current flow/depolarization through the pacemaker cell network; and (iii) depolarization-induced increase in excitability of downstream Ca(2+) stores. An analogy is provided by pendulums in an array coupled together by a network of springs. These, when randomly activated, entrain to swing at the same frequency but with a relative delay along the row giving the impression of a propagating wave. 5. The AP-like mechanism (termed voltage-accelerated Ca(2+) wave) propagates sequentially like a conducting AP. However, it is different in that it depends on regenerative store Ca(2+) release and resultant depolarization rather than regenerative activation of voltage-dependent channels in the cell membrane. 6. The applicability of these mechanisms to describing propagation in large intact gastrointestinal tissues, where voltage-dependent Ca(2+) entry is also likely to be functional, is discussed.

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ARTICLEof the total photocurrent generated by the device. The results are discussed in the context of understanding and improving the performance of polymerÀfullerene devices.