Poly 3-alkylthiophene Research Articles

Molecular Weight-Dependent Physical and Photovoltaic Properties of Poly(3-alkylthiophene)s with Butyl, Hexyl, and Octyl Side-Chains.

A series of poly-3-alkylthiophenes (P3ATs) with butyl (P3BT), hexyl (P3HT), and octyl (P3OT) side-chains and well-defined molecular weights (MWs) were synthesized using Grignard metathesis polymerization. The MWs of P3HTs and P3OTs obtained via gel permeation chromatography agreed well with the calculated MWs ranging from approximately 10 to 70 kDa. Differential scanning calorimetry results showed that the crystalline melting temperature increased with increasing MWs and decreasing alkyl side-chain length, whereas the crystallinity of the P3ATs increased with the growth of MWs. An MW-dependent red shift was observed in the UV–Vis and photoluminiscence spectra of the P3ATs in solution, which might be a strong evidence for the extended effective conjugation occurring in polymers with longer chain lengths. The photoluminescence quantum yields of pristine films in all polymers were lower than those of the diluted solutions, whereas they were higher than those of the phenyl-C61-butyric acid methyl ester-blended films. The UV–Vis spectra of the films showed fine structures with pronounced red shifts, and the interchain interaction-induced features were weakly dependent on the MW but significantly dependent on the alkyl side-chain length. The photovoltaic device performances of the P3BT and P3HT samples significantly improved upon blending with a fullerene derivative and subsequent annealing, whereas those of P3OTs mostly degraded, particularly after annealing. The optimal power conversion efficiencies of P3BT, P3HT, and P3OT were 2.4%, 3.6%, and 1.5%, respectively, after annealing with MWs of ~11, ~39, and ~38 kDa, respectively.

Preparation of Conductive Films by <i>In Situ </i>Polymerization of 3-Alkylthiophene with Soluble MWNTs

Conductive films of multi-walled carbon nanotubes (MWCNTs)/Poly3-alkylthiophene (P3TH) composite films were prepared by in-situ polymerization of 3-alkylthiophene at the presence of soluble MWCNTs. The MWCNTs were safely obtained via a two-step process assisted by microwave radiation, which were soluble in organic media. The obtained composites were examined by FTIR. By using UV-vis analysis it was found that there are strong interactions between P3TH and functionalized MWCNT. The TEM images showed the MWCNTs were homogeneously dispersed in P3TH. In addition, the resulting MWCNT/P3TH composites showed an electrical conductivity at the level 10-3 S/cm.

Poly(3-alkylthiophene) Nanofibers for Photovoltaic Energy Conversion

The use of nanostructured non-conventional semiconductors such as conjugated polymers and metal oxides (e.g. TiO2), opens promising perspectives towards a new generation of solar cells based on the concept of donor:acceptor bulk heterojunctions. In this concept donor material and acceptor material form interpenetrating networks allowing light absorption, charge transfer and charge transport throughout the entire bulk of the thin film. Since nanomorphology is of crucial importance for this type of solar cells, in this contribution the use of nanofibers in bulk heterojunction solar cells is explored in order to obtain highways for charge transport. We investigate in particular the use of P3AT (poly(3-alkylthiophene)) nanofibers and show that the polymer fraction aggregated into fibers can be easily controlled by temperature. We find an optimal efficiency at intermediate fiber fraction and show that it can be linked to the morphology of the active layer.

Preparation of Different Poly 3-Alkylthiophene Ultrathin Films at the Surface of Chemically Adsorbed Monolayer Having Thienyl Group

Polymerization processes of two types ultrathin films containing polythienyl groups anchored to the substrate surface through siloxane bonds were investigated. When the oxidative polymerization on the Chemically Adsorbed (CA) monolayer prepared with 11-(3-thienylundecyl)trichlorosilane (TTS) was performed in the acetonitrile solution containing 3-octylthiophene monomer and FeCl3, the thienyl groups in the CA monolayer and the outer 3-octylthiophene monomers were polymerized each other along the directions of both in-plane and out-of-plane of the CA monolayer. On the other hand, when the oxidative polymerization was performed without the additive 3-octylthiophene monomer, the long conjugated linkage of the thienyl groups was not formed in the CA monolayer. The highest conductivity of the film prepared with the additive 3-octylthiophene of about 10 nm thickness was 10−2 S/cm.

A Practical Approach for the Preparation of Regioregular Poly(3-hexylthiophene)

Scheme 1. Preparation of monomer Polythiophenes have been intensively studied over the last three decades. And major studies have been focused on poly 3-alkylthiophene especially poly 3-hexylthiophene (P3HT), which has shown very unique properties in conducting polymer applications. Of these, the most notable property is electrical conductivity, which is contributed to the delocalization of πelectrons through overlap of π-orbitals. In addition to this, since it is very soluble in normal organic solvents, a good processability has been observed. In general, preparation of P3HT could be achieved by either chemical or electrochemical method. For electrochemical polymerization including FeCl3 catalyzed polymerization, a potential was applied to a solution containing monomer and electrolyte. Chemical synthesis was performed by metal-mediated polymerization of monohalogenated and/or dihalogenated thiophene derivatives under appropriate conditions. An advantage in chemical polymerization over electrochemical method is that this method generally affords a highly regioregular polymer in excellent yields. Since regioregularity of P3HT is a critical element for the application of this polymer, a lot of different procedures have been developed especially in chemical synthetic methods. Generally accepted methods include metal (Ni) catalyzed self-condensation of thienyl organozinc and thienyl Grignard reagents. A big breakthrough for the preparation of regioregular P3HT has been reported by Rieke and McCullough, separately. From these works, high regioregular (> 98%) head-to-tail P3HT has been achieved with reasonable molecular weight. As mentioned above, 2,5-dibromo-3-alkylthiophenes have been extensively used as a monomer in the chemical synthetic method. However, only a few examples of using 2-bromo-5iodo-3-alkylthiopenes have been appeared in the chemical method. Recently, Knochel and co-workers introduced the application of commercially available and relative cheap zinc powder to organic synthesis. This work prompted us immediately to study the possibility of using zinc powder in the preparation of P3HT. To this end, 2-bromo-5-iodo-3-alkylthiopene could be the most proper candidate since zinc dust showed excellent insertion reactivity to carbon-iodine bond. Here, we wish to report the first result obtained from the application of the activated zinc dust to the preparation of regioregular P3HT.

Study of the order-disorder transitions in methoxy-functionalized polyalkylthiophenes

This article describes the solvatochromic properties of two polyalkylthiophene (PAT) samples functionalized at the end of the hexamethylenic side-chains with a methoxy group, which is able to strongly enhance the solubility, workability and filmability of this kind of polymers. The latter are obtained using either a regioselective or a regiospecific polymerization procedure, thus leading to a different configurational order in the final polymer. The optical features of the synthesized samples—which are very interesting for chemosensor and electrooptical applications—are observed in many solvent/non-solvent systems and derive from the conformational modification of the conjugated backbone induced by side-chain order-disorder transitions. These transitions strongly depend on the content of HT dyads; a fact which undeniably shows the importance of the polymer configuration, directly deriving from the adopted polymerization method, on the final electrical and electronic properties of the obtained material. The low sensitivity of the regioregular sample towards the temperature changes together with its higher tendency to give thick, semicrystalline and self-consisting films makes it very promising for the obtainment of organic semiconductors for electronic devices subjected to high temperature variations.

Highly processable ester-functionalized polythiophenes as valuable multifunctional and post-functionalizable conjugated polymers

A series of newly ester-substituted polyalkylthiophenes (PATEs) was prepared. All polymers were fully soluble in common organic solvents, which allowed for a wide range of physico-chemical measurements, including solvato- and thermo-chromic, thermal, microstructural and electrical (in neutral and doped state) analyses. Marked differences were observed in the material characteristics of these polyalkylthiophene derivatives. It was thus possible to identify and describe the different properties ascribable not only to the different esteric groups in side chain but also to the different average degrees of functionalization of the thiophenic repeating units. In neutral state the PATEs of this study proved to be thermostable and soluble, while at the same time exhibiting high ordered molecular assemblies leading to high average conjugation lengths, electrical conductivities and stabilities. These polymers can also be easily and quantitatively transformed in other PAT derivatives using simple nucleophilic reactions either in solution or in solid (film) state. In view of the above and given that these polymers can be profitably and inexpensively synthesized, their future use for innovative applications in the field of synthetic metals appears feasible as from now.

From polymer transistors toward printed electronics

Printed organic circuits have the potential to revolutionize the spread of electronic applications. This will be enabled by inexpensive and fast fabrication with printing techniques using soluble organic materials. Two main challenges have to be mastered on the way towards printed electronics. First, the development of stable transistors and an adapted chip design for organic materials, and second, the development of a reliable fabrication process. We present our results on high performance polymer transistors, mainly based on poly-3alkylthiophene (P3AT) as semiconducting material. Fast circuits up to 200 kHz and stable circuits with operation lifetimes of more than 1000 h under ambient conditions without any encapsulation are shown. We also report on a fully printed, all organic ring oscillator.

Plasticized conjugated polymers: a possible route to higher voltage solar cells

ABSTRACTThe introduction of propylene carbonate (PC) into the poly (3-alkyl)thiophenes (P3AT) poly(octyl)thiophene (P3OT) and poly(hexyl)thiophene) (P3HT) is studied. In both cases, we observe a diminution of their melting temperature, which demonstrates a plasticizing effect. We also observe an increase of photovoltage and photocurrent in sandwich devices M//P3AT+PC//ITO-PET where M=Al, Mg and ITO-PET is Indium thin oxide coated on polyester. We attribute this effect to the introduction of oxygen from the PC. When mixed with an electron acceptor PCBM, the photocurrents only slightly increase and the photovoltages are similar. In this case, the presence of oxygen is detrimental to the system.

Oriented thin films from soluble polythiophenes

AbstractThe degree of orientation of thin films of eight different polymeric structures, belonging to the class of soluble polyalkylthiophenes (PATs) has been studied. Thin films of the polymers, obtained by spin coating onto glass substrates, were oriented by means of the rubbing technique. The degree of orientation is related to the regioregularity of the system: highly regioregular polymers can be oriented, while regiorandom materials are not oriented. The degree of orientation can be improved by thermal annealing of the oriented films. As a result of annealing, which was performed at different temperatures according to the thermal behavior of the polymers, it was possible to increase the polarization ratio for poly(3‐decylthiophene) up to 12–13 as detected from the UV‐vis spectra in polarized light. Moreover in the investigated PATs, both the key role of molecular weight and its distribution for achieving a high orientation degree has been assessed. Copyright © 2003 John Wiley & Sons, Ltd.

Self-organization in nanoscopic poly(alkylthiophene) films on water

Ultra-thin layers (10 - 50nm) of poly(alkyl)thiophenes (PATs) spread on water from diluted chloroform solutions were studied by means of synchrotron radiation. The molecular orientation in the films was obtained using grazing incidence diffraction (GID) and reflectometry, for both doped and pristine samples. Despite alkanes being hydrophobic, the side chains tend to orient perpendicularly to the water subphase. The study reveals the presence of crystalline order with a high degree of preferred orientation. A smectic model for the polymeric layers is in good agreement with the experimental data.

Hopping transport in doped conducting polymers in the insulating regime near the metal-insulator boundary: polypyrrole, polyaniline and polyalkylthiophenes

Transport data for polypyrrole-hexafluorophosphate (PPy-PF 6), protonated polyaniline and iodine-doped regio-regular polyalkylthiophenes (PATs), all in the insulating regime near the disorder-induced metal-insulator (M-I) boundary, are presented and analyzed. These doped conducting polymers have the transport properties of a Fermi glass insulator; the disorder being characterized by the resistivity ratio, ρ r  ρ(1.4 K)/ρ(300 K). In the regime close to the M-I transition (ρ r < 10 2), the low-temperature resistivity follows Mott's variable range hopping (VRH) conduction law. Samples in the intermediate regime (10 2 < ρ r < 10 3) show crossover from the Mott to Efros-Shklovskii VRH conduction with a small Coulomb gap (Δ C ∼ 0.3–0.6 meV). For samples farther into the insulating regime (ρ r > 10 3), ρ( T) shows two distinctly different behaviors. In homogeneous material, Mott's VRH conduction is recovered. In inhomogeneous samples, where ‘metallic island’ are formed after partial dedoping or by strong morphological disorder, ln ρ ∝ (T 0′/T) 1 2 , characteristic of a granular system.

Photoexcitation spectroscopy of poly-3-alkylthiophenes

We report an extensive study of the photoexcitation properties of poly-3-alkylthiophenes (P3AT) films and solutions through measurements of UV-VIS absorption-emission, resonant Raman scattering and photoinduced absorption. From the study of the photoinduced absorption in solutions of poly-3-decilthyophene (P3DT) of different solvent quality, we conclude that interchain transfer of the charge can not be the dominant process leading to the creation of photoexcited states in solution. The possibility of the presence of photoexcited conformational defects in the solvated phase is not ruled out.

Molecular organization in polyalkylthiophene films

Different approaches for the preparation of improved-order samples of polyalkylthiophenes (PAT) have been attempted. Thermal annealing and subsequent cooling gave high-quality samples. PAT blends have been oriented. Mixed LB films of PAT and arachidic acid, have been prepared aiming to obtain PAT in a well defined molecular arrangement. These samples were studied with UV-vis. spectroscopy and X-ray diffraction: some hypothesis on the order-degree are suggested.