Morphology control of poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) block copolymer by solvent blending

The use of mixed solvents provided an effective way to control the self‐assembly behavior and photophysical properties of a conjugated rod–coil block copolymer, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO). It was shown that the balance between the π–π stacking of the P3HT and microphase separation of the copolymer could be dynamically controlled and shifted by solvent blending. Depending on the mixed solvent ratio (i.e., chloroform/methanol, anisole/chloroform, or anisole/methanol), the copolymer chains experienced different kinetic pathways, yielding a series of nanostructures such as disordered wormlike pattern, densely packed nanofibrils, and isolated nanofibrils. With the varying solvent selectivity, the P3HT‐b‐PEO chains displayed a hybrid photophysical property depending on the competition between intrachain and interchain excitonic coupling, resulting in the transformation between J‐ and H‐aggregation. Overall, this work offered an effective way to demonstrate the correlation and transformation between π–π stacking of P3HT and microphase separation, and how the conformation of P3HT chains influenced the photophysical properties of the copolymer during solvent blending. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 544–551     

Synthesis of all‐conjugated poly(3‐hexylthiophene)‐block‐ poly(3‐(4′‐(3″,7″‐dimethyloctyloxy)‐3′‐pyridinyl)thiophene) and its blend for photovoltaic applications

New all‐conjugated block copolythiophene, poly(3‐hexylthiophene)‐block‐poly(3‐(4′‐(3″,7″‐dimethyloctyloxy)‐3′‐pyridinyl)thiophene) (P3HT‐b‐P3PyT) was successfully prepared by Grignard metathesis polymerization. The supramolecular interaction between [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) and P3PyT was proposed to control the aggregated size of PCBM and long‐term thermal stability of the photovoltaic cell, as evidenced by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and optical microscopy. The effect of different solvents on the electronic and optoelectronic properties was studied, including chloroform (CL), dichlorobenzene (DCB), and mixed solvent of CL/DCB. The optimized bulk heterojunction solar cell devices using the P3HT‐b‐P3PyT/PCBM blend showed a power conversion efficiency of 2.12%, comparable to that of P3HT/PCBM device despite the fact that former had a lower crystallinity or absorption coefficient. Furthermore, P3HT‐b‐P3PyT could be also used as a surfactant to enhance the long‐term thermal stability of P3HT/PCBM‐based solar cells by limiting the aggregated size of PCBM. This study represents a new supramolecular approach to design all‐conjugated block copolymers for high‐performance photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Exploring the synthesis and impact of end‐functional poly(3‐hexylthiophene)

In recent years, end‐functional poly(3‐hexylthiophene) (P3HT) has proven to be instrumental in the continued development and innovation within the broad conjugated polymer arena, enabling a variety of applications, particularly in organic electronics. The availability of P3HT with controlled molecular weights, low polydispersity, and importantly, a wide range of reactive end‐groups not only serves as a key building block for the preparation of conjugated block copolymers but also facilitates the development of hybrid nanocomposite materials via inorganic surface modification strategies. This Highlight focuses on the synthetic approaches to end‐functional P3HT and the impact of these systems in emerging technologies. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 831–841     

One‐pot synthesis of conjugated poly(3‐hexylthiophene)‐b‐poly(phenyl isocyanide) hybrid rod–rod block copolymers and its self‐assembling properties

In this article, the synthesis of a series of conjugated rod–rod block copolymers based on poly(3‐hexylthiophene) (P3HT) and poly(phenyl isocyanide) (PPI) building blocks in a single pot is presented. Ni‐catalyzed Grignard metathesis polymerization of 2,5‐dibromo‐3‐hexylthiophene and subsequent addition of 4‐isocyanobenzoyl‐2‐aminoisobutyric acid decyl ester in the presence of Ni(dppp)Cl₂ as a single catalyst afford P3HT‐b‐PPI with tunable molecular weights and compositions. In solid state, microphase separation occurred as differential scanning calorimetric analysis of P3HT‐b‐PPI revealed two glass transition temperatures. In solutions, the copolymers can self‐assemble into spherical aggregates with P3HT core and PPI shell in tetrahydrofuran and exhibit amorphous state in CHCl₃. However, atomic force microscopy revealed that the block copolymers self‐assemble into nanofibrils on the substrate. These unique features warrant the resultant conjugated rod–rod copolymers' potential study in organic photovoltaic and other electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2939–2947     

Synthesis and morphology of all‐conjugated donor–acceptor block copolymers based on poly(3‐hexylthiophene) and poly(naphthalene diimide)

A series of all‐conjugated diblock and triblock copolymers comprised of poly(naphthalene diimide) (PNDI)‐based n‐type and the poly(3‐hexylthiophene) (P3HT) segments could be synthesized via the Kumada catalyst‐transfer polycondensation process. The crystalline structures and chain orientation of the block copolymer thin films were systematically studied by grazing incident wide‐angle X‐ray scattering (GIWAXS). The GIWAXS results indicated that both the P3HT and PNDI segments in the block copolymers form exclusive crystalline domains in which the P3HT domain aligns with an edge‐on rich orientation, and the PNDI domain aligns with a face‐on rich orientation. In contrast, the blend films of the P3HT and PNDI homopolymers also show two distinguished crystalline domains in which the P3HT domain aligns with an edge‐on rich orientation, and the PNDI domains align in different ways depending on the chemical structure of n‐type polymers, that is, PNDI1Th is isotropically dispersed, while PNDI2Th aligns with a face‐on rich orientation. In addition, the effect of thermal annealing on the crystalline behavior of the block copolymers is reported. The GIWAXS results indicated that thermal annealing increases the crystallinity of both segments without affecting their chain orientation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1139–1148     

Synthesis and self‐assembly of diblock copolymers composed of poly(3‐hexylthiophene) and poly(fluorooctyl methacrylate) segments

Regioregular poly(3‐hexylthiophene)‐b‐poly(1H,1H‐dihydro perfluorooctyl methacrylate) (P3HT‐b‐PFOMA) diblock copolymers were synthesized by atom transfer radical polymerization of fluorooctyl methacrylate using bromoester terminated poly(3‐hexylthiophene) macroinitiators in order to investigate their morphological properties. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT. The block copolymers were well characterized by ¹H NMR spectroscopy and gel permeation chromatography. Transmission electron microscopy was used to investigate the nanostructured morphology of the diblock copolymers. The block copolymers are able to undergo microphase separation and self‐assemble into well‐defined and organized nanofibrillar‐like micellar morphology. The development of the morphology of P3HT‐b‐PFOMA block copolymers was investigated after annealing in solvent vapor and also in supercritical CO₂. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Annealing effect on performance and morphology of photovoltaic devices based on poly(3‐hexylthiophene)‐b‐poly(ethylene oxide)

Novel block copolymers, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO) were synthesized via Suzuki coupling reaction of P3HT and PEO homopolymers. The copolymers were characterized by NMR, gel permeation chromatography, differential scanning calorimeter, and UV–vis measurements. A series of devices based on the block copolymers with a fullerene derivative were evaluated after thermal or solvent annealing. The device using P3HT‐b‐PEO showed higher efficiency than using P3HT blend after thermal annealing. Phase‐separated structures in the thin films of block copolymer blends were investigated by atomic force microscopy to clarify the relationship between morphologies constructed by annealing and the device performance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) via a combination of ring‐opening olefin metathesis polymerization and grignard metathesis polymerization

Novel rod–coil–rod ABA triblock copolymers, poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) (P3HT‐b‐PE‐b‐P3HT) were synthesized by using a combination of a Ru‐catalyzed ring‐opening metathesis polymerization of 1,4‐cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni‐catalyzed Grignard metathesis polymerization of 5‐chloromagnesio‐2‐bromo‐3‐hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/CTA or the initial monomer/macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT‐b‐PBD‐b‐P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT‐b‐PE‐b‐P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3810–3817     

Synthesis,micellar structures,and multifunctional sensory properties of poly(3‐hexylthiophene)‐block‐poly(2‐(dimethylamino)ethyl methacrylate) rod‐coil diblock copolymers

We report the synthesis, micellar structures, and multifunctional sensory properties of new conjugated rod‐coil block copolymers, poly(3‐hexylthiophene)‐block‐poly(2‐(di methylamino)ethylmethacrylate)(P3HT‐b‐PDMAEMA). The new copolymers, synthesized by atom transfer radical polymerization of P3HT macroinitiator, consisted PDMAEMA coil lengths of 43, 65, and 124 repeating units. All the P3HT‐b‐PDMAEMA copolymers exhibit a similar low critical solution temperature in water around 33 °C. The micellar structures of the synthesized polymers were characterized by AFM, TEM, and dynamic light scattering, by varying temperature, pH, and water/THF composition. The micelles of P3HT₂₀‐b‐PDMAEMA₄₃ in water had a reversible size change from 75 ± 5 nm to 132 ± 5 nm on heating from 25 to 55 °C and reduced to the original size during cooling. In addition, the micellar size also showed a significant pH dependence, changing from 67 ± 8 nm (pH = 12) to 222 ± 6 nm (pH = 4), depending on the protonation of the PDMAEMA blocks and their electrostatic repulsion. The micellar structure of three P3HT‐b‐PDMAEMA copolymers changed from spheres, to vesicles, and finally to larger sphere micelles as the solvent composition varied from 0 to 100 wt % water in the mixed solvent. The different micellar structures of P3HT₂₀‐b‐PDMAEMA₄₃ solution led to a red‐shift on the absorption or photoluminescence spectra and exhibited the emission colors of yellow, orange, red, and dark red with increasing the water content. This study suggested that new copolymers had potential applications as multifunctional sensory materials toward temperature, pH, and solvent. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis,morphology, and field‐effect transistor characteristics of new crystalline–crystalline diblock copolymers of poly(3‐hexylthiophene‐block‐steryl acrylate)

We report the synthesis, morphology, and charge‐transporting characteristics of new crystalline–crystalline diblock copolymers, poly(3‐hexylthiophene‐block‐stearyl acrylate) (P3HT‐b‐PSA). Three different diblock copolymers, P1 , P2 , and P3 , with P3HT/PSA polymerization degree block ratios of 60/26, 60/50, and 60/360, respectively, were prepared for investigating the morphology‐property relationship and the dependence of optoelectronic properties on the block copolymer structure. Small‐ and wide‐angle X‐ray scattering indicated the presence of both P3HT and PSA crystalline domains and the presence of microphase separation among blocks. The transmission electron microscopy and atomic force microscopy results revealed that the diblock copolymers cast from chlorobenzene, tended to form needle‐like morphologies. The field‐effect mobilities of the diblock copolymers deposited on untreated SiO₂ substrates, decreased with increasing PSA block length. In a sharp contrast, the mobilities enhanced with increasing PSA content when the P3HT‐b‐PSA was deposited on phenyltrichlorosilane (PTS)‐treated substrates. The copolymers with a 60/360 P3HT/PSA ratio showed a good mobility of 4 × 10^?3 cm² V^?1 s^?1 and a high on/off ratio of 7 × 10⁶ on PTS‐treated substrates. This study highlighted the importance of the block ratio, the substrate and self‐assembly structures on the charge transport characteristics of the crystalline–crystalline conjugated diblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Facile and versatile synthesis of rod‐coil poly(3‐hexylthiophene)‐based block copolymers by nitroxide‐mediated radical polymerization

A well‐defined and monofunctional poly(3‐hexylthiophene)‐based (P3HT) macroinitiator has been obtained through a clean, simple, and an efficient multistep synthesis process. The macroinitiator is obtained via intermolecular radical 1,2‐addition onto an ω‐acrylate‐terminated P3HT macromonomer. In a second step, well‐defined rod‐coil block copolymers were obtained by nitroxide‐mediated radical polymerization (NMRP) using the so‐called Blocbuilder^®. The polymerization was found to be controlled with various monomers such as styrene, isoprene, 4‐vinylpyridine, or methyl acrylate. This process constitutes a very promising way to obtain versatile and clean materials for organic electronics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of six‐arm star polystyrene‐block‐poly (3‐hexylthiophene) copolymer by combination of atom transfer radical polymerization and click reaction

A novel six‐arm star block copolymer comprising polystyrene (PS) linked to the center and π‐conjugated poly (3‐hexylthiophene) (P3HT) was successfully synthesized using a combination of atom transfer radical polymerization (ATRP) and click reaction. First, star‐shaped PS with six arms was prepared via ATRP of styrene with the discotic six‐functional initiator, 2,3,6,7,10,11‐hexakis(2‐bromoisobutyryloxy)triphenylene. Next, the terminal bromides of the star‐shaped PS were substituted with azide groups. Afterward, the six‐arm star block copolymer PS‐b‐P3HT was prepared using the click coupling reaction of azide‐terminated star‐shaped PS with alkynyl‐terminated P3HT. Various techniques including ¹H NMR, Fourier‐transform infrared and size‐exclusion chromatography were applied to characterize the chemical structures of the intermediates and the target block copolymers. Their thermal behaviors and optical properties were investigated using differential scanning calorimetry and UV–vis spectroscopy. Moreover, atomic force microscopy (AFM) was utilized to observe the morphology of the star block copolymer films. In comparison with two linear diblock copolymer counterparts, AFM results reveal the effect of the star block copolymer architecture on the microphase separation‐induced morphology in thin films. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(3‐hexyl thiophene)‐b‐poly(N‐isopropyl acrylamide): Synthesis and its composition dependent structural,solubility, thermoresponsive,electrochemical, and electronic properties

Conjugated block copolymers consisting of poly(3‐hexyl thiophene) (P3HT) and a thermoresponsive polymer poly(N‐isopropyl acrylamide) (PNIPAM) with varying composition have been synthesized by facile click reaction between alkyne terminated P3HT and azide terminated PNIPAM. The composition‐dependent solubility, thermoresponsive property in water, phase behavior, electrochemical, optical, and electronic properties of the block copolymers were systematically investigated. The block copolymers with higher volume fraction of PNIPAM form thermoresponsive spherical micelles with P3HT‐rich crystalline cores and PNIPAM coronas. Both X‐ray and atomic force microscopic studies indicated that the blocks copolymers showed well‐defined microphase separated nanostructures and the structure depended on the composition of the blocks. The electrochemical study of the block copolymers clearly demonstrated that the extent of charge transport through the block copolymer thin film was similar to P3HT homopolymer without any significant change in the band gap. The block copolymers showed improved or similar charge carrier mobility compared with the pure P3HT depending on the composition of the block copolymer. These P3HT‐b‐PNIPAM copolymers were interesting for fabrication of optoelectronic devices capable of thermal and moisture sensing as well as for studying the thermoresponsive colloidal structures of semiconductor amphiphilic systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1785–1794     

Energy transfer in poly(3‐hexylthiophene)‐g‐Polyfluorene graft copolymers

Conjugated graft copolymers consisting of a poly(3‐hexylthiophene) (P3HT) backbone and poly(9,9'‐dioctylfluorene) side chains (PF) with different grafting degrees were synthesized by the CuAAC reaction. The properties of these materials were studied by UV‐Vis and fluorescence spectroscopy. The former technique provides insight in their self‐assembly, while the latter is used to study the energy funneling from the PF side chains to the P3HT backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1252–1258     

Poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene): Synthesis,microphase separation,thin film transistors,and photovoltaic applications

We report the synthesis, characterization, microphase separation, field‐effect charge transport, and photovoltaic properties of regioregular poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene) (P3HT‐b‐P3cHT). Two compositions of P3HT‐b‐P3cHT (HcH63 and HcH77) were synthesized with weight‐average molecular weights of 155,500 and 210,800 and polydispersity indices of 1.45 and 1.57, respectively. Solvent‐casted HcH77 was found to self‐assemble into nanowires with a width of 12.5 ± 0.9 nm and aspect ratios of 50–120, as observed by TEM imaging. HcH77 and HcH63 annealed 280 °C were observed by small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) to be microphase‐separated with characteristic length scales of 17.0–21.7 nm. The microphase‐separated domains were shown to be crystalline with interlayer backbone (100) d‐spacings of 1.69 and 1.40 nm, which correspond to the P3HT and P3cHT blocks, respectively. Field‐effect transistors fabricated from P3HT‐b‐P3cHT thin films showed a mobility of holes (0.0019 cm²/Vs) which is independent of thermal annealing. Bulk heterojunction solar cells based on HcH77/fullerene (PC₇₁BM) blend thin films had a maximum power conversion efficiency of 2.45% under 100 mW/cm² AM1.5 solar illumination in air. These results demonstrate that all‐conjugated block copolymers are suitable semiconductors for applications in field‐effect transistors and bulk heterojunction solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 614–626, 2010     

Solubility characteristics of poly(3‐hexylthiophene)

Solubility data for poly(3‐hexylthiophene) (P3HT) in 29 pure solvents are presented and discussed in detail. Functional solubility parameter (FSP) and convex solubility parameter (CSP) computations are performed and the CSP and FSP results are compared to previously reported Hansen solubility parameters (HSPs) and to the parameters calculated using additive functional group contribution methods. The empirical data reveals experimental solubility parameters with substantial polar (δ_P) and hydrogen‐bonding (δ_H) components, which are not intrinsic to the structure of the P3HT polymer. Despite these apparent irregularities, it is shown that the predictor method based on the solubility function, f, does provide a reliable way to quantitatively evaluate the solubility of P3HT in other solvents in terms of a given set of empirical solubility data. The solubility behavior is further investigated using linear solvation energy relationship (LSER) modeling and COSMO‐RS computations of the activity coefficients of P3HT. The LSER model reveals that (1) the cavity term, δ_T, is the dominant factor governing the solubility behavior of P3HT and (2) the solvent characteristics that dictate the structural order (crystallinity) of P3HT aggregates do not similarly influence the overall solubility behavior of the polymer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1075–1087     

Improving charge transport in poly(3‐hexylthiophene) transistors via blending with an alkyl‐substituted phenylene–thiophene–thiophene–phenylene molecule

A prototypical semiconducting bicomponent system consisting of a conjugated polymer, that is, poly(3‐hexylthiophene) (P3HT), blended with a small thiophene containing conjugated molecule, that is, an alkyl‐substituted bisphenyl‐bithiophene [phenylene–thiophene–thiophene–phenylene (PTTP)], has been used as an electroactive active layer in field‐effect transistors (FETs). The self‐assembly of this bicomponent system at surfaces has been studied at different length scales, from the nanoscale to the macroscale, and compared with the behavior of monocomponent films of PTTP and P3HT. The correlation between morphology and electric properties of the semiconducting material is explored by fabricating prototypes of FETs varying the relative concentrations of the two‐component blend. The maximum charge carrier mobility value, achieved with a few percent of PTTP component, is not simply due to a uniform dispersion of the molecules in the polymer matrix, but rather to the generation of very long percolation paths, whose composition and electrical properties can be tuned with the PTTP concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Supramolecular complexes of poly(3‐Hexylthiophene)‐block (and random)‐poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] copolymers with perylene bisimide

Block and random copolymers of poly(3‐hexylthiophene) and poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] with side‐chain carboxylic functionality ((P3HT‐b‐P3COOH) and (P3HT‐r‐P3COOH) were developed by Grignard Metathesis (GRIM) polymerization. The carboxylic functionality was introduced in the side chain via the oxazoline route. Both the block and random polythiophene copolymers were complexed with pyridine functionalized perylene bisimide to obtain supramolecular block and random polymer complexes. The complex formation in both systems was confirmed by ¹H NMR, WXRD and SAXS studies. An expansion of d spacing upon complex formation was observed in both the block and random copolymer, which could be traced by WXRD. Hole and electron mobilities measured for the supramolecular complexes indicated values which were higher by an order of magnitude for the supramolecular block complex (μ_h ≈ 2.9 × 10⁻⁴ cm²/Vs; μ_e ≈ 3.1 × 10⁻⁶ cm²/Vs) as compared to the random (μ_h ≈ 1.4 × 10⁻⁵ cm²/Vs; μ_e ≈ 4.7 × 10⁻⁷ cm²/Vs) copolymer. These results are indicative of the higher degree of disorder prevailing in the films of random copolymer system compared to the block copolymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1574–1583     

Structural transitions of nanocrystalline domains in regioregular poly(3‐hexyl thiophene) thin films

The effects of solution processing and thermal annealing on thin film morphology and crystalline structures of regioregular poly(3‐hexyl thiophene) (RR P3HT) are studied in terms of molecular weight (M_w). Using grazing‐incidence X‐ray diffraction, π‐conjugated planes in drop‐cast films from chloroform solutions are found to be preferentially oriented parallel to the substrates regardless of M_w. However, the mesoscale nanocrystalline morphology of the drop‐cast films is significantly affected by M_w, exhibiting a distinctive morphological transition from short nanorods to long nanofibrils above a critical number‐averaged M_w (～ 3.6 kDa). This is probably due to the change in a conformation change from an extended‐chain to a folded‐chain, as M_w of RR P3HT increases. In contrast, spin‐casting of high M_w RR P3HT produces less ordered films with a lower crystallinity and mixed parallel/perpendicular orientations of π‐conjugated planes. The crystallinity and parallel π‐conjugated orientation of RR P3HT in spin‐cast films could be improved by thermal treatments at high‐temperatures either (1) above the glass transition temperature or (2) above the melting temperature of RR 3PHT followed by recrystallization upon cooling under vacuum. However, the charge mobility of the spin‐cast films for a field‐effect transistor application is still lower than that of the drop‐cast films. This would be attributed to the chain oxidation and the development of distinct grain boundaries between RR P3HT nanofibrils during the thermal treatments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1303–1312, 2007