Current bulk/interface structures

At the early development of polymer solar cells, a planar p-n junction structure represented the mainstream in mimicking conventional silicon-based solar cells. However, the obtained devices demonstrated poor photovoltaic performances due to the long distance between the exciton and junction interface and insufficient light absorption due to the thin light absorber. It was not until 1995 that the dilemma was overcome with the discovery of a novel bulk heterojunction in which donor and acceptor form interpenetrated phases. Poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene] was blended with Ceo or its derivatives to form the bulk heterojunction. A much improved power conversion efficiency of 2.9% was thus achieved under the illumination of 20 mW/cm. (Yu et al., 1995). The emergence of the donor/acceptor bulk-heterojunction structure had boosted the photovoltaic performances of polymer solar cells. Currently, a maximal power conversion efficiency of 10.6% had been reported on the basis of synthesizing appropriate polymer materials and designing a tandem structure (You et al., 2013). The detailed discussions are provided in Chapter 5. 

Given our current knowledge about the neat liquid interface structure and dynamics, the basic question regarding vibrational relaxation at liquid interfaces is how do these structures and dynamics affect the relaxation rate Are the same factors responsible for relaxation in bulk liquids applicable to relaxation at liquid interfaces, or, are there unique surface effects that also need to be taken into account ... 

The typical IL system could be considered as a solvent-free system, in which it can simplify the EIS analysis significantly which spurs its wide use in the characterization of the IL-electrode interface. However, due to low mobility of ions in an IL and multiple molecular interactions present in an IL, more time is needed to reach to a steady state of IL-electrode interface structure and arrangement, when a potential is applied. Furthermore, the electron-transfer process in ILs is different from that in traditional solvents containing electrolytes. Thus, the interfacial structures of IL are more complex than other systems. Even the electrode geometry could affect the EIS results of IL systems. It is noted that the bulk ILs could not be simply described by a resistor (R ) as in classic electrochemical systems. And the electrode double layer in IL electrolyte couldn t be simply depicted as a capacitor. So the Randle equivalent circuit is not sufficient to describe an IL system. Significant efforts have been made to illustrate the properties of diffusion layer and the bulk ILs with equivalent circuits. However, currently there is no general equivalent circuit model to describe the interface of an IL system. 

The past decade has seen a dramatic improvement in the strategies and instrumentation available to characterize the structures of interfacial supramolecular assemblies. Current thrusts are towards in situ techniques that probe the structure of the interfacial supramolecular assembly with increasingly fine spatial and time resolution. The objective of this field is to assemble reaction centers around which the environment is purposefully structured at the molecular level, but extends over supramolecular domains. The properties of the assembly are controlled not only by the properties of the molecular building blocks but especially by the interface. Therefore, the focus is on both the interfacial and bulk properties of monolayers and thin films. Issues that need to be addressed include the film thickness, structural homogeneity and long-range order, as well as the electrochemical and... 

Carbon supported Pt and Pt-alloy electrocatalysts form the cornerstone of the current state-of-the-art electrocatalysts for medium and low temperature fuel cells such as phosphoric and proton exchange membrane fuel cells (PEMECs). Electrocatalysis on these nanophase clusters are very different from bulk materials due to unique short-range atomic order and the electronic environment of these cluster interfaces. Studies of these fundamental properties, especially in the context of alloy formation and particle size are, therefore, of great interest. This chapter provides an overview of the structure and electronic nature of these supported... 

Since the reaction rate at potentials above Vp is limited by the dissolution of oxide and the dissolution rate depends on the nature of the oxides (see Chapter 4), the change of current with potential indicates that oxide composition/structure varies with the formation. The nonstoichiometric composition of an anodically formed oxide film can be expressed as SiO with a higher value of n close to the oxide/electrolyte interface and a lower value of n close to the Si/oxide interface.A thicker oxide film has a bulk composition closer to the stoichiometric SiOa. The dissolution rate of anodic oxide depends on the composition of the electrolyte as shown in Fig. 5.46. " (also Fig. 5.7 ). It depends little on the type of material and doping levels. ... 

We have shown that the fracture toughness of interfaces between polymers is dependent on the molecular structure at the interface as well as on the bulk properties of the polymers on either side of the interface. This relationship is now relatively well established for glassy polymers and the main results are summarized in Figs. 53 and 54, as well as in Sects 3.2-3.5. However, these results should be used with caution when the polymers on either side of the interface are rubbery or semicrystalline. The stress-transfer mechanisms, and in particular the role of the entanglements, will be very different from those observed for the glassy polymers and only preliminary data are currently available on those systems. In principle, fracture mechanisms maps analogous to those depicted in Figs. 53 and 54 could be drawn for these systems but the relevant parameters are not yet as clearly identified. 

This current state has to do with the discovery that the action of fundamental adhesion forces is not restricted to the interface. They not only fix some layer of adhesive molecules on the surface of the adherend but they can exert strong influence on the formation of chemical and morphological structure as well as on molecular mobility in the adjacent region of the adhesive during solidification. Hence an interphase is formed. These interphases depend on the combination of adhesive and adherend surface and on the process of contact formation as well. Due to its distinct structure, the interphase possesses properties that can be much different from the behavior of the bulk adhesive. Compared to the complexity of the problem, we just start understanding what is behind interphases. 

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