Polythiophenes morphology

Howard lA, Mauer R, Meister M, Laquai F (2010) Effect of morphology on ultrafast free carrier generation in polythiophene fullerene organic solar cells. J Am Chem Soc 132 14866... 

The soluble polythiophenes are the first conducting polymers that can be taken above their glass transition without decomposition and it will be interesting to study morphology-property relationships. Heeger et al.262) have recently described conformational changes in solutions of poly-3-hexylthiophene which seem to involve a coil-helix transformation as the temperature is decreased or a poor solvent is added. 

Kaneto et al.523) have made measurements on the diffusion of lead perchlorate in polythiophene by following the colour change. They found a diffusion coefficient which varied from 10-1° to I0-12 cm2 s 1, depending upon the applied potential. The complexities introduced by morphological heterogeneity, counter-ion motion and solvent effects mean that further studies will be required to determine the relative importance of factors affecting diffusion in these materials. 

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

The him morphology of electrochemically prepared polythiophene has been shown in numerous studies to be almost identical to that commonly observed for polypyrrole (described in Chapter 2). A nodular surface is observed for both unsubstituted and 3-alkyl substituted thiophenes.92 As with PPy, the electrochemical preparation of PTh at higher current densities produced rougher surface morphologies. The similarity in morphologies suggest a similar growth mechanism for electrochemically polymerized PPy and PTh. 

Hassenkam, T., Greve, D.R., and Bjomhohn, T., Direct visualization of the nanoscale morphology of conducting polythiophene monolayers studied by electrostatic force microscopy, Adv. Mater. 13, 631-634, 2001. 

Liu, J.S. et al., Tuning the electrical conductivity and self-assembly of regioregular polythiophene by block copolymerization Nanowire morphologies in new di- and triblock copolymers, Angew. Chem. Int. Ed. 41, 329, 2001. 

Savenije, T.J. et ah. The effect of thermal treatment on the morphology and charge carrier dynamics in a polythiophene-fullerene bulk heterojunction, Adv. Fund. Mater. 15, 1260-1266, 2005. 

A polythiophene anode in an aqueous electrolytic system, showed irreversible changes at a potential beyond 0.9 V on repeated reduction, suggesting that the breakdown into lower oligomers occurs, as evident from its Raman spectra [268]. However, the loss of electroactivity, electrical conductivity, electrochromic properties, mechanical properties, compact morphology... 

L. Pigani, R. Seeber, F. Terzi, O. Cerri, M. Innocenti, R. Udisti, and G. Sanna, Relaxation phenomena and structural modifications of substituted polythiophenes during the p-doping processes. An electrochemical and morphological study. Electrochim. Acta, 51, 2698 (2006). 

Some polymers (e.g., polyacetylene and polythiophene ) exhibit an additional morphological heterogeneity consisting of fibrils of dense material dispersed in a void, such that the polymer material and dopants occupy only about 50% of the volume. Although the sample is formally heterogeneous within the solid material, constituent phases are in such close proximity that not only may it be difficult to distinguish a boundary between them, but the constituents of the microdomains themselves are uncertain. Even single crystals which have been... 

---