Poly optical models

In Sect. 2.1 we discussed the many applications of optical modelling for organic solar cells. The case study we chose to present as one application of optical modelling of organic solar cells is the analysis of parasitic absorption losses in the different layers of the solar cell stack. One example is shown in Fig. 8. We calculated the absorptance of each layer in a layer stack glass/ITO (160 nm)/poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT PSS) (30 nm)/poly[(4,40-bis (2-ethylhexyl)dithieno [3,2-h 20,30- 7 silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,l,3-benzothiadiazole)-5,50-diyl] (SiPCPDTBT) [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) (100 nm)/Ca (20 nm)/Al(100 nm). The transfer matrix formalism... 

Poly(para-phenylenevinylene)s (PPVs) represent one of the most intensively investigated classes of rr-conjugated materials. Many synthetic procedures to generate unsubstituted and substituted PPVs have been developed. They include 1,6-polymerizations of 1,4-xylylene intermediates as well as several polycondensation methods. Parallel to the polymer syntheses, several series of PPV oligomers (OPVs) have been synthesized and characterized. Such model oligomers of different molecular size allow for a study of the dependence of electronic and optical properties on the length of the conjugated Ti-system. 

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

In the case of poly-benzofuran (86 ), the optical purity has not been even roughly evaluated, as no optically active model compounds are known, to which reference can be made. 

A remarkable enhancement of optical activity has been observed for the most stereoregular fractions of poly-a-olefins, with respect to the optical activity of the low-molecular-weight model compounds (Table 9). 

As in the case of poly-a-olefins, only in some poly-vinyl-ethers in which the asymmetric carbon atom of the lateral chains is in the ft position with respect to the principal chain and in which the optical activity is remarkably higher than in low molecular weight models, it was found that the optical activity and its temperature coefficient remarkably depend on the stereoregularity of the sample. 

Interesting results have been observed by investigating complexes of some poly-vinyl-ethers with tri-isobutyl aluminum. It was noticed that the variation of the optical activity on complexing poly-vinyl-ethers with tri-isobutyl aluminum is of the same type as in the low-molecular-weight model compounds (66, 111, 113b, 123). 

A comparison between the optical activity of some poly-acrylic or poly-methacrylic esters and of some model compounds, having approximately the same optical purity, shows that in general the optical activity is in both cases of the same order of magnitude (Table 19). 

Both in poly-a-olefins and in poly-vinyl-ethers, which are the most systematically investigated optically active vinyl polymers, the chromo-phoric systems responsible for the optical activity appear to be in the same spectral region of those of the low-molecular-weight models 66. 105,113a). 

Birshtein and Luisi (17) made attempts to prove the theoretical validity of the above model by applying the theory of VOLKENSTEIN (137, 138, 139), Birshtein and Ptitsyn (16) on the conformation of isotactic macromolecules, to optically active poly-a-olefins. From their results it is possible to conclude that the presence of asymmetric carbon atoms in the lateral chains might cause the prevalence of main chain sections spiraled in one of the two possible screw senses, mainly for entropic reasons. 

The optical rotatory dispersion of poly-(+)-l-methyl-benzyl-methacry ate has been measured between 320 and 230 raft. The optical activity for polymer and model has values of the same sign and of the same order of magnitude, but the isotactic polymer seems to have a larger [M] than the syndiotactic and the atactic polymers [K. J. Liu, J. S. Lignowski, R. Ullman ACS Polymer Preprints, 6, 904 (1965)]. Optically active N-methyl-N-methylbenzyl-acrylamide and N-(n-propyl)-N-methylbenzyl-acrylamide have been polymerized by Kaiser and Schulz and the optical rotation dispersion between 589 raft and 365 raft has been... 

As discussed in section 7.1.6.4, semidilute solutions of rodlike polymers can be expected to follow the stress-optical rule as long as the concentration is sufficiently below the onset of the isotropic to nematic transition. Certainly, once such a system becomes nematic and anisotropic, the stress-optical rule cannot be expected to apply. This problem was studied in detail using an instrument capable of combined stress and birefringence measurements by Mead and Larson [109] on solutions of poly(y benzyl L-glutamate) in m-cresol. A pretransitional increase in the stress-optical coefficient was observed as the concentration approached the transition to a nematic state, in agreement of calculations based on the Doi model of polymer liquid crystals [63]. In addition to a dependence on concentration, the stress-optical coefficient was also seen to be dependent on shear rate, and on time for transient shear flows. 

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