Preparation of porous poly(3‐hexylthiophene) by freeze‐dry method and its application to organic photovoltaics

Poly(3‐hexylthiophene)(P3HT) with a microporous network structure was prepared from a 1% p‐xylene solution by freeze‐dry method. Scanning electron microscopy (SEM) showed P3HT molecules formed swollen gel‐like structures with different extent of compactness depending on the length of the aggregation period. Absorption spectrum of this P3HT film showed a characteristic peak at 620 nm, which indicated a high degree of order between polymer chains. Photoluminescence (PL) of this highly ordered P3HT film appeared at 712 nm revealing large extent of π–π stacking between P3HT molecules in the freeze‐dry film. Both absorption and photoluminescence results indicated that the original aggregated states of P3HT molecules in gel form had been preserved throughout the freeze‐dry operation. X‐ray diffraction of the annealed samples showed a strong characteristic peak for the side chain aggregation at 2θ = 5.1°, which proved that the freeze‐dry film was with highly order structure. The interconnected and highly ordered P3HT film is used in the study of organic photovoltaics (OPV) after applying an n‐type semiconductor to the surface of the dry porous fibers. A prototype OPV device with power conversion efficiency of 1.47% was prepared by this method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Preparation of a poly(3‐hexylthiophene)‐grafted indium tin oxide/poly(3‐hexylthiopene) composite and its conductivity–temperature characteristics

The temperature–conductivity characteristics of poly(3‐hexylthiophene) (P3HT) composites filled with P3HT‐grafted indium tin oxide (ITO) particles were investigated in this work. The ITO particles were first treated with a silane coupling reagent of 3‐aminopropyltriethoxysilane (APS), and then thiophene rings were introduced through a condensation reaction between the ending amino groups of APS and the carboxylic groups of thiophene‐3‐acetic acid. The composites were prepared by the polymerization filling of the 3‐hexylthiophene (3HT) monomer with the thiophene‐ring‐introduced ITO particles. Elemental analysis, Fourier transform infrared, and X‐ray photoelectron spectroscopy were used to confirm the grafting reaction on the ITO surface. The longer the polymerization time was or the higher the 3HT/ITO feeding ratio was, the more P3HT was grafted. The influence of the grafted amount on the electrical properties of ITO particles was attributed to the wrapping effect formed by the grafted P3HT on the surface of the ITO particles. The conductivity change of the P3HT‐grafted ITO/P3HT composites was proved to be subject to the change in the average gap width of ITO interparticles, which was determined by the filling ratio of P3HT to ITO in the polymerization and the volume expansion effect of a P3HT thin film between neighboring ITO particles during the heating process. In comparison with the ungrafted ITO/P3HT composites, the grafting treatment enhanced the interaction between the particles and polymer matrix, and this was helpful for obtaining a more homogeneous dispersion structure for the composites and thus afforded a higher positive temperature coefficient intensity and better reproducibility. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1881–1888, 2006     

Synthesis and characterization of poly(3‐hexylthiophene)–poly(3‐hexyloxythiophene) random copolymers with tunable band gap via Grignard metathesis polymerization

A series of 3‐substituted polythiophene copolymers having different side chain arrangements of hexyl and hexyloxy groups has been synthesized via the Grignard metathesis (GRIM) method and systematically studied. Despite differences in monomer reactivity ratios for the nickel‐catalyzed chain transfer polymerization, random sequences of hexyl‐ and hexyloxy‐substituted polythiophenes with different monomer compositions and adjustable band‐gap energies can be synthesized according to their respective comonomer feed ratio, as evidenced from NMR, UV, electrochemical measurements, and computational calculations. Structural characterization from X‐ray diffraction measurements reveals that the flexible hexyloxy side chains of the monomer significantly affect the crystallinity and molecular packing of the random copolymers. This study shows potential for synthesizing random copolymers with different monomer reactivities via the GRIM method for future optoelectronic applications. © 2014 Society of Chemical Industry     

Effect of [6,6]‐phenyl‐C61‐butyric acid methyl ester on the morphology of poly(3‐hexylthiophene) film

The change of morphology of poly(3‐hexylthiophene) (P3HT) film as a result of blending with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was studied using a freeze‐dry method. A porous structure was observed as the P3HT/PCBM solution was freeze‐dried. The pore size decreased as the proportion of PCBM increased in the P3HT/PCBM blended film. Additionally, the freeze‐dried P3HT/PCBM film was more resistant to the formation of PCBM crystals than that prepared by a spin‐coating method during the thermal annealing process. Homogeneous distribution of PCBM in the freeze‐dried P3HT/PCBM film was the main reason for the reduction of large PCBM crystal formation. Copyright © 2011 Society of Chemical Industry     

Miscibility enhancement through hydrogen bonding interaction of biodegradable poly(3‐hydroxybutyrate) blending with poly(styrene‐co‐vinyl phenol) copolymer

Differential scanning calorimetry, one‐ and two‐dimensional Fourier transform infrared (FTIR), and solid state nuclear magnetic resonance (NMR) spectroscopy have been used to investigate the miscibility of and specific interactions between poly(styrene‐co‐vinyl phenol) (PSOH) and poly(3‐hydroxybutyrate) (PHB) upon varying the vinyl phenol content of the PSOH copolymer. The FTIR and solid state NMR spectra revealed that the phenol units of PVPh interact with the carbonyl groups of PHB through intermolecular hydrogen bonding. A miscibility window exists when the vinyl phenol fraction in the copolymer is greater than 22 mol % in the PSOH/PHB blend system, as predicted using the Painter–Coleman association model. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of heterocyclically conjugated poly(3‐hexylthiophene)–clay nanocomposite materials

A series of heterocyclically conjugated polymer–clay nanocomposite (PCN) materials that consisted of organic poly(3‐hexylthiophene) (P3HT) and inorganic montmorillonite (MMT) clay platelets were prepared by in situ oxidative polymerization with FeCl₃ as an oxidant. The as‐synthesized PCN materials were characterized by Fourier transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (WAXRD), and transmission electron microscopy (TEM). The effects of the material composition on the anticorrosion, gas barrier, thermal stability, flammability, mechanical strength, and electrical conductivity properties of the P3HT and PCN materials were studied by electrochemical corrosion measurements, gas‐permeability analysis (GPA), thermogrametric analysis (TGA), limiting oxygen index (LOI) measurements, dynamic mechanical analysis (DMA), and a four‐point probe technique, respectively. The molecular weights of extracted and bulk P3HT were determined by gel permeation chromatography (GPC) with THF as an eluant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3438–3446, 2004     

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

A combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μ_h and μ_e) values increased considerably. The best charge mobilities were acquired for the P3HT₅₀₀₀₀:PC71BM:rGO‐g‐P3HT₅₀₀₀₀:P3HT₇₀₀₀‐b‐PS₁₀₀₀ system (μ_h = 1.9 × 10^?5 cm² V^–1 s^–1 and μ_e = 0.8 × 10^?4 cm² V^–1 s^–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10^?4 and 2.7 × 10^?3 cm² V^–1 s^–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm^?2, 0.63 V, 62% and 4.35% to 12.98 mA cm^?2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry     

Poly(lactic acid)/poly(3‐hexylthiophene) composite nanofiber fabrication for electronic applications

Fibers of the biopolymer poly(lactic acid) (PLA) and the p‐type semiconducting polymer poly(3‐hexylthiophene) (P3HT) were fabricated using the electrospinning technique at low PLA concentration (5 wt%) in CHCl₃. The fibers were several millimeters long and had diameters in the range 100 nm–4 µm. Nanofibers containing 63%/37% of PLA/P3HT were electroactive, and therefore were used to construct p–n diodes whose ideality parameter was 2.4 and rectification (on/off) ratio was 400 at ±1 V. These diodes were also able to sense UV radiation and remain operable with an increase in the on/off ratio and a lowering of the turn‐on voltage. By fabricating reusable and low‐cost multifunctional diodes from PLA/P3HT, the applications of PLA as a biocompatible and biodegradable polyester are expanded to include electronic device fabrication with low environmental impact. © 2016 Society of Chemical Industry     

Controlling the morphology of poly(3‐hexylthiophene)/methanofullerene film through a dynamic‐cooling and freeze‐drying process

A dynamic‐cooling and freeze‐drying (DCFD) process has been applied to the fabrication of polymer solar cells. The dynamic‐cooling process allows poly(3‐hexylthiophene) molecules to aggregate in solution into a more organized structure during the cooling process; the freeze‐drying process prevents severe agglomeration of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) during the solvent removing process. Application of these two processes to the preparation of the poly(3‐hexylthiophene)/methanofullerene photoactive layer results in an enhanced poly(3‐hexylthiophene) aggregation and smaller PCBM agglomerates. Devices fabricated using the DCFD process generate 14% more in current density than those prepared by the spin‐coating process under AM1.5G illumination. © 2015 Society of Chemical Industry     

Crystalline and Conductive Poly(3‐hexylthiophene) Fibers

Intrinsically conducting polymer fibers are prepared from P3HT by melt spinning. High crystallinity is achieved by drawing the fibers after the spinning process, applying a draw ratio of 1:2. DSC and XRD measurements confirm the continuous increase of crystalline phases with drawing. For comparison, poly(ethylene terephthalate) fibers are coated with P3HT and drawn as well. Again, the drawing of the coated fiber results in a significant increase in crystallinity of the P3HT coating. The high amount of crystalline phases is associated with a dramatic increase in conductivity (350 S · cm^?1) after doping with FeCl₃ in nitromethane.

     

Identification of the possible defect states in poly(3‐hexylthiophene) thin films

The possible origins of a low density of defect states within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap are suggested for regioregular poly(3‐hexylthiophene). A number of “chemical” defects, impurities, and structural defects could contribute to features in photoemission for regioregular poly(3‐hexylthiophene), observed within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap of regioregular poly(3‐hexylthiophene). POLYM. ENG. SCI., 47:1359–1364, 2007. © 2007 Society of Plastics Engineers     

Temperature‐conductivity characteristics of the composites consisting of fractionated poly(3‐hexylthiophene) and conducting particles

Poly (3‐hexylthiophene) (P3HT) synthesized by oxidative polymerization was fractionated by molecular weight by using organic solvents. The fraction of higher average molecular weight gave higher regioregularity and conductivity. Composites of the P3HT fraction having the highest molecular weight were prepared by use of the following conducting particles as fillers: titanium carbide (TiC), indium tin oxide (ITO), and carbon black (CB). Temperature‐conductivity profiles of the composites showed that the resistance change with PTC (positive temperature coefficient) effect was strongly influenced by the content and size of conducting particles and the molecular weight of P3HT. Although no significant PTC effect for P3HT‐CB composite and little effect for P3HT‐ITO composite system were observed, the P3HT‐TiC composite containing TiC of 70–80 wt % showed an obvious PTC effect that brought the conductivity change by about four orders of magnitude near the glass transition temperature of P3HT. However, such a remarkable PTC effect was not observed for the P3HT‐TiC composite prepared with the P3HT fraction of low‐molecular weight. It was shown that a good PTC effect could be achieved by the composite consisting of the P3HT of high‐molecular weight and the conducting particles of relatively large size. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3069–3076, 2000     

All polymer PTC devices: Temperature‐conductivity characteristics of polyisothianaphthene and poly(3‐hexylthiophene) blends

The present article is concerned with the temperature‐conductivity characteristics of blends consisting of polyisothianaphthene (PITN) particles and a soluble poly(3‐hexylthiophene) (P3HT). PITN was synthesized by direct conversion of 1,3‐dihydroisothianaphthene (DHITN) monomer using N‐chlorosuccinimide (NCS) as an oxidation/dehydrogenation reagent. The high conductivity and thermal stability of the doped and dedoped PITN were confirmed. Microscopic investigation by scanning electron microscopy (SEM) showed that the as‐prepared PITN exhibited diversified shapes and sizes, with large rectangular particles having an average size of 2 ～ 5μm and fine round particles ranging from 0.1 to 0.3 μm. The PITN particles were blended with the chemically synthesized P3HT as a high conductivity component to improve the conductivity and simultaneously maintain the positive temperature coefficient (PTC) effect of the original P3HT near its melting point. The temperature‐conductivity characteristics for PITN‐P3HT blends with various PITN contents showed that a blend having both a high conductivity (nearly 3 ～ 4 orders higher than that of the original P3HT) and a good PTC intensity could be obtained with a PITN content of 20 ～ 25%. The different temperature‐conductivity behavior of P3HT blends filled with PITN as compared to other conducting particles, for example, carbon black, was explained by its unique dispersion structure due to a relatively higher adhesive interaction of PITN particles with the P3HT matrix during the precipitation process. The results from heating recycles revealed that the PTC effect of PITN‐P3HT blends was not just related to the conductivity decrease of the P3HT matrix, arising from the conformational change of the conjugated backbone during the melting, but also to the dilution effect of the conducting percolation network due to the mobility of PITN particles induced by the viscosity decrease of the P3HT matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1848–1854, 2005     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001     

Electrical and mechanical characteristics of composites consisting of fractionated poly(3‐hexylthiophene) and conducting particles

The dynamic viscoelasticity of fractionated poly(3‐ hexylthiophene)titanium carbide (P3HT/TiC) composites was examined with regard to their electrical characteristics. The elastic modulus (E′) at 0°C [i.e., near the glass‐transition temperature (T_g) of P3HT] increased with increasing TiC content of the composite. In particular, composites whose TiC content exceeded the threshold concentration showed a high E′. This was caused by the high E′ of TiC and the strong interaction between TiC and P3HT. When the sample was heated above the T_g, E′ decreased rapidly and an increase in the loss tangent appeared near the T_g of P3HT. Mechanical loss was caused by friction between TiC and P3HT. The change in mechanical characteristics affected the electrical conductivity. When the TiC content of the composite approximated to the threshold concentration, a significant change in mechanical characteristics took place, so that a large positive temperature coefficient (PTC) effect was observed near the T_g. To explain the PTC phenomenon, we propose a model of conductive pathway for P3HT/TiC. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1429– 1433, 2002     

Photocarrier mobility in poly(2‐methoxyaniline)

In the current study the mobility of photogenerated charge carriers in PMA [poly(2‐methoxyaniline)] and their transport were investigated using time‐of‐flight (TOF) techniques. Also studied was the effect on hole mobility of film thickness and of the method of polymer processing during device fabrication. The highest value of hole mobility found was 4.5 × 10⁻⁴ cm² V⁻¹ s⁻¹ at an applied field of 1.3 × 10⁶ V/cm and 293 K in solution‐cast film of PMA. The hole mobility of solution‐cast films was about 2 orders of magnitude higher compared to spin‐coated films, for which the ordering of the polymer chains may be the reason. To our knowledge, this is the first time the TOF mobility of this material has been presented. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1506–1512, 2001     

Nonisothermal crystallization behaviors of poly(3‐hexylthiophene)/reduced graphene oxide nanocomposites

Poly(3‐hexylthiophene) (P3HT)/reduced graphene oxide (rGO) nanocomposites were prepared through in situ reduction of graphene oxide in the presence of P3HT. The nonisothermal crystallization behaviors of P3HT and P3HT/rGO nanocomposites were investigated by differential scanning calorimetry. The Avrami, Ozawa, and Mo models were used to analyze the nonisothermal kinetics. The addition of rGO remarkably increased the crystallization peak temperature and crystallinity of P3HT, but the crystallization half‐time revealed little variation. The crystallization activation energies were calculated by the Kissinger equation. The results suggested that rGO plays a twofold role in the nonisothermal crystallization of P3HT, that is, rGO promotes the crystallization of P3HT as nucleating agent, and meanwhile, it also restricts the motion of P3HT chains. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modification of poly(3‐hydroxybutyrate)‐co‐poly(3‐hydroxyvalerate) with natural rubber

Composites of poly(3‐hydroxybutyrate)‐co‐poly(3‐hydroxyvalerate) (PHBHV) with 6% of 3‐hydroxyvalerate (HV) and natural rubber (NR) were prepared by a solvent‐casting method. Different approaches were tested for the composite preparation. Both PHBHV and NR were dissolved in chloroform, followed by its evaporation, giving various layers. The mechanical properties and morphology of the obtained composites were evaluated by tensile tests and scanning electron microscopy (SEM), respectively. The obtained results demonstrated that the final composite has excellent mechanical properties when compared with PHBHV. SEM analysis unequivocally showed the excellent adhesion between the two polymeric layers. This new material was also tested as a drug delivering system using flurbiprofen as a model drug, and then the diffusion coefficients were determined. This article describes an easy method to produce a desirable composite from PHBHV and NR. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010