Heterolayered structure

In this work we have chosen the combination of hole-conducting copper-phthalocyanine (CuPc) and the n-conducting fullerene C o, which are both known from organic photovoltaic cells either as heterolayer structures or bulk-heterojunctions [18-21]. They can be considered as model systems for ambipolar transport where the asymmetry of the electron and hole mobilities is adjustable by the concentration of both materials in the mixture. 

Electropolymerization method is one of the most interesting method to control the copolymer composition in molecular sequence or chain sequence, drastically. Accordingly, in the case that the property of the electropolymerized material is electro-conductive and insoluble, a heterolayer structure and/or a sloped structure with conducting polymers are constructed on the electrode. 

Shimizu, Y. and Egashira, M. Sensitization of odor semiconductor gas sensors by employing a heterolayer structure. In Sensors Update Sensor Technology — Applications — Markets, Baltes, H., Gopel, W., and Hesse, J., Eds. VCH Weinheim, 1999, Vol. 6, pp. 211-229. 

F. H. Pollack, Effects of Homogeneous Strain on the Electronic and Vibrational Levels in Semiconductors J. Y Marzin, J. M. Gerard, P. Voisin, and J. A. Brum, Optical Studies of Strained III—V Heterolayers R. People and S. A. Jackson, Structurally Induced States from Strain and Confinement M. Jams, Microscopic Phenomena in Ordered Superlattices... 

Lee, TL (1999) High-Resolution Analysis of Adsorbate-Induced GaAs(001) Surface Structures and Strain in Buried III-V Semiconductor Heterolayers by X-ray Standing Waves. PhD Dissertation, Northwestern University, Evanston, Illinois... 

Figure 5. Structure of Type II heterolayer superlattice and emission peak shift as a function of layer thickness, (solid line is estimated from Kronig-Penny model. 

Figure 2 shows the band structures of several homopolymers and pyrrole-bithiophene copolymers estimated by electrochemical and optical methods as examples. A combination of these homopolymers and/or copolymers implies various kinds of superlattice structures. The electrochemical preparation of both homopolymer multiheterolayers and/or copolymer multiheterolayers results in a superlattices. The electrochemical copolymerization method as used to prepare heterolayers was easier than in the homopolymer heterolayers. The copolymer multi heterolayers are prepared by simply changing the applied electrode potential. On the contrary, the latter needs exchange of the mother solutions. The present electrocopolymerization method which makes compositionally modulated copolymer heterolayers possible is considered to be one of the most fascinating methods to fabricate organic superlattices. 

These observed photoluminescence spectral properties of conjugated polymer heterolayers fabricated by the present PPEP method appear to be due to quantum size effects. However, additional studies of these materials will be necessary to establish the true origin of their properties. In any case, these results also suggest that many other novel structures of functional materials and devices can be fabricated by this method. 

A preparative method directed toward control of any kind of depth structure of the conducting polymer heterolayers has been developed with a... 

Perhaps because of the wide difference in their oxidation potentials, there are only a few studies of the random copolymerization of these two important heterocyclic monomers. This difference, however, provides an excellent opportunity to fabricate conducting heterolayers by applying the PPEP method to this copolymerization, which is detailed elsewhere [19]. The structure of multilayers on the potential sweep function and the dimension of each layer can be lowered to 20 A. Alternate-layered, stairlike-layered and triangular-sloped structures are fabricated by rectangular potential, step, and triangular sweep functions, respectively. 

The charge carrier balance problem has been minimized by the introduction of multilayered polymeric structures that produce potential barriers at the internal interfaces. These potential barriers impose restrictions to charge carrier transport through the device and enhance the recombination probability and, consequently, the device efficiency. One example of such a structure is the rrO/PPV/CN-PPV/metal LED. CN-PPV presents a higher electroafiinity and ionization potential than PPV, so that there is a potential barrier for electron transport from the CN-PPV to the PPV and a potential barrier for holes in the opposite direction [218]. Several other conjugated polymers and molecules are also used in combination with PPV in heterolayer LEDs [213]. 

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