Poly doped structure

Keeping abrupt profiles of dopants is also required to apply the FLA technique to solar cell fabrication process. Figure 11.8 shows secondary ion mass spectroscopy (SIMS) profiles of Cr and P atoms in the bottom layers and of B in the surface doping layer of p-i-n Si stacked films before and after FLA, the structure of which is also schematically shown [34]. The abrupt profiles of the surface B atoms as well as of the bottom Cr and P atoms are maintained after FLA, which results from millisecond-order rapid annealing, and shows the possibility of immediate formation of p-i—n poly-Si structure with only one irradiation of flash lamp for p-i-n stacked a-Si layers. 

Schematically show and compare the results of n-doping of a conventional semiconductor (e.g. Si with P) and a CP (e.g. poly(thiophene) with tetrafluo-roborate), using band structure diagrams, and molecular (for Si) and chain (for poly(thiophene)) structures. 

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

A preferable system is poly(p-fluorostyrene) doped into poly(styrene). Since rotations about the 1,4 phenyl axis do not alter the position of the fluorine, the F spin may be regarded as being at the end of a long "bond" to the backbone carbon. In standard RIS theory, this polymer would be treated with dyad statistical weights to automatically take into account conformations of the vinyl monomer unit which are excluded on steric grounds. We have found it more convenient to retain the monad statistical weight structure employed for the poly(methylene) calculations. The calculations reproduce the experimental unperturbed dimensions quite well when a reasonable set of hard sphere exclusion distances is employed. 

Recently, Lipton et al. [25] have used zinc-67 NMR to investigate [Zn(HB(3,5-(CH3)2pz)3)2] complexes which have been doped with traces of paramagnetic [Fe(HB(3,4,5-(CH3)3pz)3)2]. The low-temperature Boltzmann enhanced cross polarization between XH and 67Zn has shown that the paramagnetic iron(II) dopant reduces the proton spin-lattice relaxation time, Tj, of the zinc complexes without changing the proton spin-lattice relaxation time in the Tip rotating time frame. This approach and the resulting structural information has proven very useful in the study of various four-coordinate and six-coordinate zinc(II) poly(pyrazolyl)borate complexes that are useful as enzymatic models. 

P. Barta, P. Dannetun, S. Stafstrom, M. Zagorska, and A. Pron, Temperature evolution of the electronic band structure of the undoped and doped regioregular analog of poly(3-alkylthio-phenes) a spectroscopic and theoretical study, J. Chem. Phys., 100 1731-1741, 1994. 

Polyphthalamides (PPA), 10 216-217 ASTM standards for, 19 793 Poly(p-phenylene) (PPP), 22 207t 23 717 conducting, 7 523, 527 molecular structure of, 22 211 optical band gap, 7 529t room temperature conductivity, 7 532 water-soluble, electroactive, self-doped sulfonatoalkoxy-substituted, 23 720 Poly(p-phenylene benzobisoxazole) (PBO), 19 714... 

For instance, poly-p-phenylenes in their doped states manifest high electric conductivity (Shacklette et al. 1980). Banerjee et al. (2007) isolated the hexachloroantimonate of 4" -di(tert-butyl)-p-quaterphenyl cation-radical and studied its x-ray crystal structure. In this cation-radical, 0.8 part of spin density falls to the share of the two central phenyl rings, whereas the two terminal phenyl rings bear only 0.2 part of spin density. Consequently, there is some quinoidal stabilization of the cationic charge or polaron, which is responsible for the high conductivity. As it follows from the theoretical consideration by Bredas et al. (1982), the electronic structure of a lithium-doped quaterphenyl anion-radical also differs in a similar quinoidal distortion. With respect to conformational transition, this means less freedom for rotation of the rings in the ion-radicals of quaterphenyl. This effect was also observed for poly-p-phenylene cation-radical (Sun et al. 2007) and anion-radical of quaterphenyl p-quinone whose C—O bonds were screened by o,o-tert-hutyl groups (Nelsen et al. 2007). 

A number of poly(arylene vinylene) (PAV) derivatives have been prepared. Attachment of electron-donating substituents, such as dimethoxy groups (structure 19.3), acts to stabilize the doped cationic form and thus lower the ionization potential. These polymers exhibit both solvatochromism (color changes as solvent is changed) and thermochromism (color is temperature-dependent). 

FIGURE 19.2 Poly-p-phenylene resonance structures after doping. 

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