Jun Tsukamoto

Structure and electrical properties of polyacetylene yielding a conductivity of 105 S/cm

We have prepared polyacetylene (ν-(CH)x) yielding a conductivity of more than 105 S/cm, by making some modifications on Naarmann et al.s method. Structural analyses of this polymer were carried out by use of various analysis techniques such as SEM, IR and resonance Raman spectroscopy to characterize ν-(CH)x. No distinct differences in structure between conventional polyacetylene and ν-(CH)x were observed except for morphology and specific gravity. Upon iodine doping, conductivity increases stepwisely, which may suggest the formation of a staging structure and/or the transformation to metallic phase. However, in the temperature dependence of conductivity, we could not find any differences which distinguish the metallic ν-(CH)x from conventional polyacetylene.

Recent structural investigations of metallic polymers

Abstract Recent structural studies of the undoped and iodine-doped polyacetylenes (prepared by the Tsukamoto and co-workers method), PF 6 − -doped polypyrrole and polyaniline emeraldine base and (hydrochloric acid and camphorsulfonic acid) salts are presented. Some key features of the polymer chain array and its evolution with the conditions of preparation are emphasized. Special attention has been devoted to characterization of the various sources of structural disorder in the relationship with high conductivity and related properties exhibited by these three families of polymers. Variation in the structural order in both crystalline and amorphous regions correlates directly with the electrical and optical properties of the metallic state.

Inhomogeneous disorder and the modified Drude metallic state of conducting polymers

Abstract The metallic state of the very highly conducting doped polymers, such as polyacetylene, polypyrrole and polyaniline, is shown to have remarkable similarities. Though each of these doped polymers has a different temperature-dependent conductivity, each of these doped polymer systems has a similar metal-like Pauli susceptibility and density of states at the Fermi level. Also, each of these highly conducting systems displays a universal electronic response (dielectric constant and conductivity) as a function of frequency from the microwave regime (10 9 Hz) through to the ‘all conduction electron plasma frequency’ (1 to 3 eV, depending on the polymer). This common behavior despite apparent differences in the temperature-dependent conductivities is proposed to be a consequence of the inhomogeneous crystalline order in these materials, leading to three-dimensional metallic domains or islands (crystallographically coherent regions), separated by poorly conducting weak links (disordered regions and interfiber links).

Characteristics of Schottky barrier solar cells using polyacetylene, (CH)x

Abstract We have constructed Schottky barrier solar cells using semiconductive polyacetylene, and investigated their characteristics which are influenced significantly by the surface conditions of the polyacetylene films. The surface contacting the glass wall during polymerization has greater trap density, and the device having a Schottky barrier on the surface shows inferior characteristics to that having a barrier on the other surface. The energy conversion efficiency was improved up to 1%, when the incident light intensity was 7 mW/cm 2 and the energy of 0.2 mW/cm 2 was input into the barrier region through the Al electrode. From the strong dependence of the photovoltaic current on the backward biasing voltage, it is inferred that excitons contribute to the photocarrier generation.

Quinoxaline-based π-conjugated donor polymer for highly efficient organic thin-film solar cells

A quinoxaline-based π-conjugated donor polymer, poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5′,8′-di-2-thienyl-2′,3′-diphenylquinoxaline)] (N-P7), was synthesized to achieve a high power conversion efficiency (PCE) of bulk heterojunction (BHJ)-based solar cells. The optical band-gap and highest occupied molecular orbital level of N-P7 were 1.95 and −5.37 eV, respectively. BHJ-based solar cells using N-P7 as a donor and phenyl C71 butyric acid methyl ester as an acceptor gave a PCE as high as 5.5% under AM 1.5G 100 mW/cm2 illumination. We also investigated the effects of substituent groups of quinoxaline-based polymers on the morphology of the BHJ layer.

On the metallic states in highly conducting iodine-doped polyacetylene

Abstract The temperature dependences of the conductivity, the magnetic susceptibility and the thermoelectric power of iodine-doped highly conducting ( ca. 10 5 S/cm) polyacetylene are presented. The conductivity shows non-activated behavior down to mK region. The density of states derived from the susceptibility and the thermoelectric power is consistent with one-electron band calculation. The electron localization due to the quasi one-dimensionality inherent to polymer is considered to beviolated by mesoscopic potential disorder, resulting in metallic strands, which are connected by tunneling.

The Metallic State of Conducting Polymers: Microwave Dielectric Response and Optical Conductivity

Recent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, e, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, e increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative e is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm -1 . Below 600 cm -1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm -1 ) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative e demonstrating the intrinsic metallic nature of the new generation of conducting polymers.

147 fs, 51 MHz soliton fiber laser at 1.56 µm with a fiber-connector-type SWNT/P3HT saturable absorber

We fabricated a fiber-connector-type saturable absorber in which SWNTs and P3HT (poly-3-hexylthiophene) were coated on the connector end. The pulse width was 147 fs and the repetition rate reached as high as 51 MHz.

A 113 fs fiber laser operating at 1.56 μm using a cascadable film-type saturable absorber with P3HT-incorporated single-wall carbon nanotubes coated on polyamide

We successfully fabricated a cascadable film-type single-wall carbon nanotube (SWNT) saturable absorber coated on aromatic polyamide film, in which the saturable absorption effect can be controlled with the number of films. A conductive polymer P3HT (poly-3-hexylthiophene) was adopted to obtain a uniform SWNT solution. We applied saturable absorber films to a passively mode-locked fiber laser and successfully generated a 113 fs, 42 MHz pulse by inserting two film layers between fiber connectors in the cavity.

Influence of Small Amounts of Dispersed Single-Walled Carbon-Nanotubes on the Optical Properties of Poly-3-hexylthiophene

We studied the dispersion of single-walled carbon-nanotubes (SWNTs) in poly-3-hexylthiophene (P3HT) and the influence of their dispersion on the optical properties of the polymer. The bundles of SWNTs were found to be well dispersed in P3HT solution, being broken up into finer ropes. We also found that dispersal of only a small amount (less than 1 wt%) of SWNTs in P3HT gives rise to a steep increase in optical absorbance close to the absorption edge, remarkable quenching of photoluminescence, and formation of oriented micro-domains. These results suggest that an ordered structure in the conjugation of P3HT is formed by the incorporation of SWNTs.