Poly 3-octylthiophene Research Articles

Metal contact properties of poly3-octylthiophene thin films

Abstract Chemically synthesized undoped poly3-octylthiophene (P3OT) was deposited as thin films on conducting glass substrates by drop casting. Doping state of P3OT was obtained by adding FeCl 3 into the original P3OT solution. A qualitative explanation of the electrical contact behavior of the P3OT films was given by a band diagram made from optical absorbance spectra and electrochemical current–voltage curves of the polymeric films. Gold contacts on both undoped and doped P3OT films give an ohmic contact. Silver/P3OT contact shows a rectifying behavior; the forward current is 500 times the reverse current at 0.5 V. Aluminum also forms rectifying contact with the two types of P3OT films, although the experimental rectification ratio is lower than that of the silver. The I–V curves of rectifying contacts were analyzed with Schottky equation and different diode parameters were obtained.

Electrochemical impedance spectroscopy of poly(3-methylthiophene) and poly(3-octylthiophene) film electrodes

Charge transfer processes in poly-3-methylthiophene (PMT) and poly-3-octylthiophene (POT) film electrodes bathed with 0.05–0.5 M LiClO 4 acetonitrile solutions were studied by cyclic voltammetry and electrochemical impedance spectroscopy. Semi-circle parameters R ct and C dl, Warburg constant σ w, effective diffusion coefficients D eff, and low-frequency capacities C LF were determined for PMT and POT films as functions of the bathing electrolyte concentration and the electrode potential. A comparison between the results of electrochemical studies of PMT and POT modified electrodes is performed in the paper.

Investigation of ink-jet printing of poly-3-octylthiophene for organic field-effect transistors from different solutions

Organic field-effect transistors (oFETs) have been developed and investigated using commercially available poly-3-octylthiophene (P3OT). Test devices have been prepared on Al-Si/SiO2 gate/gate-oxide with lift-off patterned electrodes of Ti/Au on top. Finally, the semiconductor has been deposited and patterned by ink-jet printing using a piezoelectric actuated microfluidic pipette. The solvent revealed to be the key parameter for ink-jet printing. We did not succeed in printing well defined patterns from a common chloroform based solution. Tri-chlorethylene worked better yielding proper single dots, but lines were printed with stacked dots only and, as a result the transistor behaviour remained poor. Best results have been obtained using chlorobenzene or xylene as solvent with a P3OT concentration of around 1mg/ml. Using these inks lines of about 180μm in width have been printed on top of electrode spaces with 15–50μm channel width. Although ink-jet printing led to thick edge bulges at the side walls of the dots, this has not to act to the smaller channels within. In between the bulges of jetted lines we obtained films with comparatively uniform thicknesses depending on concentration. Measured oFET characteristics yielded field-effect hole mobilities of up to 2×10−3cm2/Vs for 1mg/ml P3OT in xylene. Because ease of patterning compared to other approaches we conclude that ink-jet printing offers a very versatile technology for deposition and patterning of organic field-effect transistors for low cost electronics.

AC conductivity of conjugated polymer onto self-assembled aligned carbon nanotubes

This work focuses on the combination of the complementary properties of carbon nanotube (CNT) thin film and poly3-octylthiophene (P3OT), following a dielectric route to the characterization of a novel composite material. The structural and electrical characterization of a P3OT/CNTs hybrid system performed by X-ray diffraction, differential scanning calorimetry and a.c. impedance spectroscopy show interesting effects, including the tendency of the nanotube structure to nucleate crystal growth and substantial changes in the dielectric behavior of the polymer, due to the effect of the polymer on the nanotube conformation. Dielectric relaxation spectroscopy demonstrates that the crystallization of the polymer onto the nanotubes results into a different relaxation of the composite's electronic structure. The changes in the dielectric properties can be explained in terms of a reduced vibrational freedom of the polymer chains as a consequence of the intercalation of the polymer matrix into the nanotubes’ lattice.

Aerosol Synthesis of Anatase Titanium Dioxide Nanoparticles for Hybrid Solar Cells

Using an aerosol technique, in which ultrasonically formed droplets of titanium isopropoxide are pyrolyzed, thin films of nanosized anatase titanium dioxide (TiO2) particles are deposited. The size of the particles and the morphology of the films depend on the deposition parameters, i.e., reaction temperature, concentration of the precursor, and gas flow. Under optimal conditions, films can be deposited which consist of stoichiometric anatase TiO2 particles with diameters of 50−300 nm. With these films, solar cells are constructed by spin casting poly(3-octyl)thiophene (P3OT) on top. Devices with a 1-μm film of porous TiO2 and P3OT inside the pores have a short circuit current (Isc) of 0.25 mA/cm2, an open circuit voltage (Voc) of 0.72 V, a fill factor (FF) of 0.35, and an efficiency (η) of 0.06% under white light illumination (1000 W/m2). The efficiency is a factor of 20 higher than that of cells based on flat films of anatase TiO2, whereas the OD for both systems is comparable (flat film equivalent of 60-nm P3OT). The incident photon to current efficiency (IPCE) for the nanostructured solar cell is 2.5% at 488 nm. Devices prepared by adding P3OT during the deposition of the porous TiO2 show the same performance as the cells where P3OT is applied after TiO2 deposition. This shows that penetration of the polymer is quite effective in this system. It is found that P3OT can penetrate these porous TiO2 films as deep as 1 μm.

Frequency dependent electrical transport between conjugated polymer and single-walled carbon nanotubes

This work focuses on the combination of the complementary properties of single-walled carbon nanotube (SWNTs) and poly3-octylthiophene (P3OT), following a dielectric route to the characterization of a novel composite material. The structural and electrical characterization of a SWNT/P3OT hybrid system performed by differential scanning calorimetry and a.c. impedance spectroscopy show interesting effects, including the tendency of the nanotube structure to nucleate crystal growth and substantial changes in the dielectric behavior of the polymer, due to the effect of the polymer on the nanotubes conformation. In particular, the curve peak of the imaginary part of the impedance spectra shows a shift to a higher frequency demonstrating that the crystallization of the polymer onto the nanotubes results into a different relaxation of the composite's electronic structure, as would be expected from a strong polymer-tube interaction. Raman spectroscopy is finally applied to suggest that in the composite film the changes in the dielectric properties can be explained in terms of a reduced vibrational freedom of the polymer chains as a consequence of the intercalation of the polymer matrix into the nanotubes’ lattice.

Preparation of a nanostructured composite of titanium dioxide and polythiophene: a new route towards 3D heterojunction solar cells

Using an aerosol technique, in which ultrasonically formed droplets of titanium tetraisopropoxide are pyrolysed, thin films of nanosized particles of anatase TiO 2 can be deposited. The size of the particles and the film morphology are strongly dependent on deposition parameters like reaction temperature, concentration of the precursor, and gas flow. At best, films can be formed consisting of homogeneous, stoichiometric anatase TiO 2 particles with a size of about 50 nm. With these films, solar cells have been constructed by spin casting poly(3-octyl)thiophene (P3OT) on top. Cell characteristics of the devices with a 300 nm film of TiO 2 and an equivalence of 30 nm of PT inside the pores are I sc=0.25 mA/cm 2, V oc=0.72 V, FF=0.35 and η=0.06% using white light with an intensity of 1000 W/m 2 (not AM 1.5). The IPCE is 2.5% at 488 nm.

Electronic properties and optical studies of luminescent polythiophene derivatives

The poly 3-(2-(5-chlorobenzotriazolo)ethyl)thiophene (PCBET) was synthesized by directly introducing an electron transporting moiety on the side chain that can receive electrons efficiently. The PCBET in various molecular weights (Mw) shows a remarkable enhancement in luminescent intensity compared to that of polyoctylthiophene (POT). This improvement can be attributed to the high efficiency in electron transport by lowering the lowest unoccupied molecular orbital (LUMO) level with respect to that of POT. Electronic properties of polymers in different Mw were also studied.

Photoinduced FT-IR spectroscopy and CW-photocurrent measurements of conjugated polymers and fullerenes blended into a conventional polymer matrix

In this work we present an investigation of the photoexcited states in conjugated polymer (donor) – fullerene (acceptor) interpenetrating networks embedded into conventional polymer hosts like polystyrene (PS), polyvinylcarbazole (PVK) or polyvinylbenzylchloride (PVBC) (guest – host approach), using photoinduced FT-IR spectroscopy. We discuss the influence of the specific host polymer matrices on the photoexcited states of the photoactive guests and investigate the photoinduced electron transfer by analysis of the infrared activated vibrational (IRAV) bands of poly-3-octylthiophene (P3OT) in comparative studies. Solar cells based on mixtures of poly [2-methoxy, 5-(3′,7′-dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV), a highly soluble fullerene derivative [6,6]-phenyl C 61-butyric acid methyl ester (PCBM) and a conventional polymer (PS, PVK or PVBC) are characterized. We studied the current–voltage characteristics of devices and determined the energy conversion and electron/photon conversion efficiencies.

Exceptional anisotropy in conductivity and mechanical properties of poly-3-octylthiophene films

Poly-3-octylthiophene (P3OT) films electrodeposited onto stainless steel substrates at a current density of 0.5 mA/cm 2 were found to exhibit ultra high tensile strength of 127 MPa. The outstanding anisotropy in conductivity of the P3OT film was also observed, and the conductivity along the direction parallel to the plane was about 10 5 times as much as that measured along the direction perpendicular to the plane of the P3OT film, which was higher than that (10 4) of single crystals of graphite. Various experimental parameters affecting the anisotropy in conductivity were studied.

Time resolved photoinduced electron spin resonance studies on conjugated polymer fullerene mixtures in solution

Abstract We report results of cw- and transient ESR investigations on mixtures of P3OT (poly-3-octylthiophene) and C 60 in solution. In pristine C 60 solutions with xylene or ODCB ( ortho -dichlorobenzene) as solvent the dominant LESR signal is the C 60 triplet. In solutions of P3OT and C60 in xylene a change of the decay dynamics of the C 60 triplet state is observed. Photoinduced C 60 − has not been observed in the investigated solutions.

Field Emission from Polymers

ABSTRACTCarbon based materials are considered to be amongst the most promising field emitters for use in displays. Semiconducting polymer (regioregular poly3 octylthiophene) has been found by the authors to have the lowest threshold field reported to date for any carbon based material. The emission process is, we believe, associated with surface irregularities, voids, possibly resulting from solvent evaporation. Field intensification occurs, and as a consequence there is field emission from the top ridges of the voids. The current flowing through these regions is controlled by space charge in traps in the upper half of the energy gap. There is, in addition, current injected from the base of the voids and the two currents mix to give field emission with current IαV1.8 where V is the anode voltage. Measurements on capacitor samples using Aluminium, Gold and Calcium electrodes have been used to examine the conduction processes in the material and these are linked to results of field emission to further illuminate the mechanisms involved and provide a model for the emission process.

Electrical properties of FeCl 3-doped polyethylenevinylacetate-polyoctylthiophene blends

We have studied the electrical transport properties of a new polymer blend consisting of polyoctylthiophene (POT) melt processed into a polyethylenevinyl-acetate (EVA) matrix. The EVAPOT blend doped with FeCl 3 has a room temperature dc conductivity σ dc (300K) varying from 10 −8 Ω −1cm −1 to 1Ω −1cm −1 with increasing doping. The temperature dependence of σ dc fits σ dc (T) = σ 0 exp[-( T 0/ T) 1 2 ] , especially in highly conducting samples where the conduction can be described by the granular metal model. This conclusion is supported by the small metallic thermoelectric power which varies linearly with temperature.