Poly(3‐hexylthiophene) aggregation at solvent–solvent interfaces

The aggregation behavior of P3HT is investigated at the interface of orthogonal solvents for P3HT. The changeable characteristics of P3HT aggregate dispersions, for example, extent of aggregation and intrachain order, are studied by varying (1) the interfacial area, (2) the poor solvent used to induce aggregation – dichloromethane (DCM), hexane (HEX), and acetonitrile (AcN) – and (3) the relative composition of the good solvent, chloroform (CF), and poor solvents. The results are compared to those observed using rapid injection of the solvent. Miscibility gap values (Δδ) provide a reasonable justification of the assembly behavior of P3HT in the solvent mixtures in terms of the kinetics of polymer aggregation and the kinetics of solvent mixing at the interface. Atomic force microscopy (AFM) is used to analyze the morphology of films processed from dispersions with disparate characteristics, but having the same solvent composition, for example, 70:30 CF:HEX or 60:40 CF:DCM. Based on the disparity of the kinetics and miscibility gap values, the prevalence of specific structural motifs in the films, for example, spheroids (globules) and fibers, is effectively rationalized in terms of the structural attributes of the aggregates in the liquid phase rather than the evaporation rate (boiling point) differences of the solvents in the mixture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 999–1011     

Poly(3‐hexylthiophene) films prepared using binary solvent mixtures

Binary solvent mixtures were routinely used to induce the hierarchical assembly of poly(3‐hexylthiophene) (P3HT) in the liquid phase. This technique has garnered a lot of interest as a route to well‐organized films and composites, but, to date, the impact that the attributes of the liquid‐phase aggregates and solvent mixtures have on the organization of the films have only been partially scrutinized. The molecular weight and concentration dependence of P3HT assembly in three binary solvent mixtures containing chloroform and acetonitrile, n‐hexane, or dichloromethane were studied using ultraviolet/visible absorbance spectroscopy and dynamic light scattering techniques. Films drop cast under slow and rapid evaporation conditions were observed using optical and atomic force microscopy. In general, there is no evidence that the characteristics of the liquid phase P3HT aggregates impact the structures of the films, but films cast from these solvent mixtures under rapid evaporation conditions exhibit an array of disparate morphologies and mesoscale patterning. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 624–638     

P3HT/graphene composites synthesized using In situ GRIM methods

Poly(3‐hexylthiophene)/graphene (P3HT/G) materials are synthesized using an in situ Grignard metathesis approach. The structural properties and spectroscopy of the materials are studied using NMR, FTIR, and UV–vis absorption spectroscopies, wide‐angle X‐ray scattering, atomic force microscopy and cyclic voltammetry. P3HT regioregularities ≥90% are observed in composites with approximate graphene compositions as high as 20% by weight. ¹H and ¹³C NMR spectra of liquid phase dispersions reveal signals that are not observed in pristine P3HT. The intensity of these signals correlates with the graphene content, thereby indicating that the graphene is influencing the polymerization process. Anomalous features in the FTIR spectra of P3HT/G powders are also observed. AFM images of P3HT/G films show morphological differences between P3HT on graphene compared with P3HT domains on the silicon substrates. Cyclic voltammetry reveals a monotonic decrease in the energy of the HOMO and LUMO levels of P3HT with increasing graphene loading. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 60–76     

Controlled dispersion of polystyrene‐capped Au nanoparticles in P3HT:PC61BM and consequences upon active layer nanostructure

Numerous recent publications detail higher absorption and photovoltaic performance within organic photovoltaic (OPV) devices which are loaded with Au or Ag nanoparticles to leverage the light management properties of the localized surface plasmon resonance (LSPR). This report details the impact upon film morphology and polymer/nanoparticle interactions caused by incorporation of polystyrene‐coated Au nanoparticles (Au/PS) into the P3HT:PC₆₁BM bulk heterojunction film. Nanostructural analysis by transmission electron microscopy and X‐ray scattering reveals tunable Au/PS particle assembly that depends upon the choice of casting solvent, polymer chain length, film drying time, and Au/PS particle loading density. This Au/PS particle assembly has implications on the spectral position of the Au nanoparticle LSPR, which shifts from 535 nm for individually dispersed particles in toluene to 650 nm for particles arranged in large clusters within the P3HT:PC₆₁BM matrix. These results suggest a critical impact from PS/P3HT phase separation, which causes controlled assembly of a separate Au/PS phase in the nanoparticle/OPV composite; controlled Au/PS phase formation provides a blueprint for designing AuNP/OPV hybrid films that impart tunable optical behavior and potentially improve photovoltaic performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 709–720     

The origin of DC electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) films

We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σ_dc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f_R) and static dielectric constant (ε₀) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010     

Synthesis of block copolymers comprised of poly(3‐hexylthiophene) segment with trisiloxane side chains and their application to organic thin film transistor

The demand of stretchability for a semiconducting polymer has increased to realize wearable devices and sensors. However, studies involving intrinsically stretchable π‐conjugated polymers are still limited. Here, we develop a soft‐polythiophene derivative, P3SiHT, with a trisiloxane unit in the side chains via a hexylene spacer unit. In addition, diblock (P3HT‐b‐P3SiHT) and triblock (P3HT‐b‐P3SiHT‐b‐P3HT) copolymers could be synthesized based on Kumada catalyst‐transfer polycondensation. The results of atomic force microscopy and grazing incidence small‐angle X‐ray scattering indicate that the block copolymer thin films form a phase‐separated structure between the P3HT and P3SiHT domains. The organic thin film transistor devices were prepared to assess the electrical properties of the block polymers. As a result, the block copolymers showed comparable or even higher hole mobility than that of P3HT homopolymer, thus due to the enhanced phase‐separation and thereby charge transportation. The mechanical test of the bulk films indicates that P3HT‐b‐P3SiHT‐b‐P3HT shows lower tensile modulus and longer elongation at break than P3HT homopolymer and other diblock copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1787–1794     

Solution processing of polymer semiconductor: Insulator blends—Tailored optical properties through liquid–liquid phase separation control

It has been demonstrated that the 0‐0 absorption transition of poly(3‐hexylthiophene) (P3HT) in blends with poly(ethylene oxide) (PEO) could be rationally tuned through the control of the liquid–liquid phase separation process during solution deposition. Pronounced J‐like aggregation behavior, characteristic for systems of a low exciton band width, was found for blends where the most pronounced liquid–liquid phase separation occurred in solution, leading to domains of P3HT and PEO of high phase purity. Since liquid–liquid phase separation could be readily manipulated either by the solution temperature, solute concentration, or deposition temperature, to name a few parameters, our findings promise the design from the out‐set of semiconductor:insulator architectures of pre‐defined properties by manipulation of the interaction parameter between the solutes as well as the respective solute:solvent system using classical polymer science principles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 304–310     

Impact of side‐chain length on the phase structures of P3ATs and P3AT:PCBM films as revealed by SSNMR and FTIR

It is known that poly(3‐alkylthiophene) (P3AT) side‐chain length notably influences the photovoltaic performances of relating devices. However, comprehensively study on its impact on the structures of P3ATs and their blends with [6, 6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) is insufficient. By using solid‐state NMR and FTIR techniques, four P3ATs and their PCBM blends are investigated in this work, focusing on the phase structures as modulated by side‐chain length. Recently, we revealed multiple crystalline main‐chain packings of packing a and b together with a mesophase in poly(3‐butylthiophene) (P3BT) films (DOI: 10.1021/acs.macromol.6b01828). Here, the semicrystalline structures are investigated on poly(3‐hexylthiophene) (P3HT), poly(3‐octylthiophene) (P3OT), and poly(3‐dodecylthiophene) (P3DDT) with traditional form I modification, where packing a and the amorphous phase are probed. Furthermore, crystallized side chain within packing a is detected in both P3OT and P3DDT films, which shows a FTIR absorption at 806 cm⁻¹. Structural studies are also conducted on P3AT:PCBM blends. Compared with the pure P3ATs, the polymer crystallinities of the blends show reduction of about 40% for P3OT and P3DDT, whereas only about 10% for P3HT. Moreover, in P3BT:PCBM and P3HT:PCBM, the crystalline polymers and PCBM are phase separated, while in P3OT:PCBM and P3DDT:PCBM, blend components are mostly miscible. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 751–761     

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     

Structure and morphology control in thin films of regioregular poly(3‐hexylthiophene)

This review focuses on the structural control in thin films of regioregular poly(3‐hexylthiophene) (P3HT), a workhorse among conjugated semiconducting polymers. It highlights the correlation existing between processing conditions and the resulting structures formed in thin films and in solution. Particular emphasis is put on the control of nucleation, crystallinity and orientation. P3HT can generate a large palette of morphologies in thin films including crystalline nanofibrils, spherulites, interconnected semicrystalline morphologies and nanostructured fibers, depending on the elaboration method and on the macromolecular parameters of the polymer. Effective means developed in the recent literature to control orientation of crystalline domains in thin films, especially by using epitaxial crystallization and controlled nucleation conditions are emphasized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1218–1233, 2011     

Electro‐optical properties of electropolymerized poly(3‐hexylthiophene)/carbon nanotube composite thin films

3‐hexylthiophene was electropolymerized on a carbon nanotube (CNT)‐laden fluorine‐doped tin oxide substrate. Scanning electron microscopy and Raman spectroscopy revealed that the polymer was infused throughout the thickness of the 150‐nm thick CNT mat, resulting in a conducting composite film with a dense CNT network. The electropolymerized poly(3‐hexylthiophene) (e‐P3HT)/CNT composites exhibited photoluminescence intensity quenching by as much as 92% compared to the neat e‐P3HT, which provided evidence of charge transfer from the polymer phase to the CNT phase. Through‐film impedance and J‐V measurements of the composites gave a conductivity (σ) of 1.2 × 10^?10 S cm^?1 and zero‐field mobility (μ₀) of 8.5 × 10^?4 cm² V^?1 s^?1, both of which were higher than those of neat e‐P3HT films (σ = 9.9 × 10^?12 S cm^?1, μ₀ = 3 × 10^?5 cm² V^?1 s^?1). In electropolymerized samples, the thiophene rings were oriented in the (010) direction (thiophene rings parallel to substrate), which resulted in a broader optical absorbance than for spin coated samples, however, the lack of long‐range conjugation caused a blueshift in the absorbance maximum from 523 nm for unannealed regioregular P3HT (rr‐P3HT) to 470 nm for e‐P3HT. Raman spectroscopy revealed that π‐π stacking in e‐P3HT was comparable to that in rr‐P3HT and significantly higher than in regiorandom P3HT (ran‐P3HT) as shown by the principal Raman peak shift from 1444 to 1446 cm^?1 for e‐P3HT and rr‐P3HT to 1473 cm^?1 for ran‐P3HT. This work demonstrates that these polymer/CNT composites may have interesting properties for electro‐optical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1269–1275, 2011     

Metal Free Acid‐Mediated Solid‐State Polymerization and Processability of Polymers Based on 3,4‐Alkylenedioxythiophenes

The present article reports metal free acid‐mediated polymerization of 3,4‐alkylenedioxythiophenes in a solvent free medium and processability of insoluble polymers. It also describes structural variants and functional aqueous dispersions based on 3,4‐alkylenedioxythiophenes. Polymers were processed by dispersing the insoluble polymer powders in aqueous media using polymeric aromatic surfactant (polystyrenesulfonate, PSS) and aliphatic surfactant (sodiumdodecylsulfonate, SDS), respectively. The effect of surfactant on particle size, stability, and conductivity of the dispersions was investigated in detail. Polymer particles in SDS‐based dispersions tend to agglomerate which resulted enhanced conductivity of the thin films. Electrochemical studies revealed that the polymers are electroactive in nature and are transparent in oxidized state. The electrochromic contrast between the oxidized and reduced states of the polymers was in the range of 40–46%. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 783–791     

Decreased domain size and improved crystallinity by adjusting solvent–polymer interaction parameters in all‐polymer solar cells

We have investigated the effect of solvent–polymer interaction on the morphology, crystallinity, and device performance of poly‐(3‐hexylthiophene) (P3HT) and poly{2,7‐(9,9‐didodecyl‐fluorene)‐alt‐5,5‐[4′,7′‐bis(2‐thienyl)‐2′,1′,3′‐benzothia‐diaole]} (PF12TBT) blend system. 3‐Hexylthiophene (3‐HT), which had the similar structural units with both donor and acceptor materials, was chosen as the solvent additive to be added into the main solvent chlorobenzene (CB), to adjust the solvent–polymer interaction. With the 3‐HT percentage increasing from 5 to 30% in CB solution, the solvent–polymer interaction between polymer and solvent molecules decreased slightly according to the calculated solubility parameters (δ) and interaction parameters (χ₁₂). As a result, nanoscale phase‐separated and interconnected morphology with decreased domain size of both donor and acceptor was formed. Meanwhile, the order of P3HT molecule was enhanced which resulted from the extended film drying time and increased molecular planarity after incorporation of 3‐HT. The power conversion efficiency (PCE) had a gradual improvement to 1.08% as the 3‐HT percentage reached 10%, which can be attributed to the enhanced short‐circuit current (J_sc) and fill factor (FF). However, when the 3‐HT percentage exceeded 20%, the decreased J_sc and FF ultimately decreased the PCE. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 288–296     

Insights into poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) block copolymer: Synthesis and solvent‐induced structure formation in thin films

We report the synthesis, characterization, and solvent‐induced structure formation in thin films of an amphiphilic rod‐coil conjugated block copolymer, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide). The diblock copolymers were prepared by a facile click reaction and their characterizations as well as thermal, crystalline, optical properties, and self‐assembly behavior have been investigated in detail. A series of morphologies including two‐phase separated nanostructure, nanofibrils, and their mixed morphology could be obtained depending on the selectivity of solvents to different blocks. Structural analyses demonstrate there is a subtle balance between microphase separation of copolymer and the π‐π stacking of the conjugated P3HT and such balance can be controlled by changing the solvents of different selectivity in solution and the length of P3HT block. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Depth-resolved molecular structure and orientation of polymer thin films by synchrotron X-ray diffraction

An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), hereinafter P3HT, deposited by spin casting onto silicon substrates functionalised by three selected molecules and then properly annealed, has been examined. Grazing Incidence X-ray Scattering (GIXS) measurements have been performed with 4-circle diffractometer, allowing for a fine control of sample axes movement.By choosing different grazing incident angles, diffraction patterns from different layers of polymeric thin films have been recorded. Both in-plane and out-of-plane geometries have been combined in order to obtain complementary structural information. In this way structural and orientational differences of the polymer along with the film thickness (?50 nm) have been highlighted. For all P3HT films spun on functionalized Si wafer, macromolecular layers close to the substrate surface give some evidence of higher order and orientation than those outmost the surface, and this behaviour is pronounced to a different extent depending on the functionalized molecules used. Contrariwise P3HT layers deposited onto bare Si wafer display reduced orientation and decreased crystallite size, especially at buried interface.     

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     

Monte Carlo morphological modelling of a P3HT:PCBM bulk heterojunction organic solar cell

To deepen the understanding of morphology evolution in bulk heterojunction P3HT:PCBM organic photovoltaics system by thermal treatment, domain‐size‐dependent interfacial energies were first determined by coarse‐grained molecular dynamics modelling and then used in Monte Carlo simulations of the morphology evolution. Thereby initial conditions associated with optimal interfacial surface area, continuous volume, as well as domain sizes, and spatial distributions of the phase separated domains were identified. In line with earlier studies, a 1:1 P3HT:PCBM blend ratio is found to exhibit the most efficient morphology for exciton dissociation and charge transport. Our simulations reveal that preseeding of P3HT crystal at the anode side prior to the annealing process will be instrumental to pin the formation of P3HT at the favorable electrode especially when seeding exceeds a threshold of 10% surface coverage, whereas denser seeding patterns beyond the threshold did not improve the active layer morphology further. The observed trilayer depth profile (in the absence of preseeded P3HT crystals) implies that the commonly used thickness 100 nm of the active layer is not ideal for ensuring that donor and acceptor phases dominate at opposite ends of the active layer. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 270–279     

Study of spatial inhomogeneity in inverted all‐polymer solar cells: Effect of solvent and annealing

The efficiency optimization of bulk heterojunction solar cells requires the control of the local active materials arrangement in order to obtain the best compromise between efficient charge generation and charge collection. Here, we investigate the large scale (10–100 μm) inhomogeneity of the photoluminescence (PL) and the external quantum efficiency (EQE) in inverted all‐polymer solar cells (APSC) with regioregular poly(3‐hexylthiophene) (P3HT):poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) active blends. The morphology and the local active polymer mixing are changed by depositing the active layer from four different solvents and by thermal annealing. The simultaneous PL and EQE mapping allowed us to inspect the effects of local irregularities of active layer thickness, polymer mixing, polymer aggregation on the charge generation and collection efficiencies. In particular, we show that the increase of the solvent boiling point affects the EQE non‐uniformity due to thickness fluctuations, the density non‐uniformity of rrP3HT aggregate phase, and the blend components clustering. The thermal annealing leads to a general improvement of EQE and to an F8BT clustering in all the samples with locally decrease of the EQE. We estimate that the film uniformity optimization can lead to a total EQE improvement between 2.7 and 6.3 times. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 804–813