P3HT Block Research Articles

Improved Self-Assembly of P3HT with Pyrene-Functionalized Methacrylates.

A block copolymer with discotic liquid crystalline behavior was synthesized using Grignard metathesis polymerization (GRIM) and initiators for continuous activator regeneration atom transfer radical polymerization (ICAR-ATRP). A novel discotic liquid crystalline mesogen, 6-(pyren-1-yloxy)hexyl methacrylate (PyMA), comprises a block that is attached to regioregular poly(3-hexylthiophene) (rr-P3HT) generated by GRIM and subjected to end-group modification. Due to the continuous regeneration of Cu+ in the reaction mixture in ICAR-ATRP compared to conventional methods, the synthesis was successfully performed with less catalyst. The purity and yield of the final product are increased by eliminating rigorous post-synthesis purification. Stacked pyrene units have contributed to the enhanced long-range π–π interactions and aligning of the P3HT block as observed in thin-film X-ray diffraction (XRD). Furthermore, field-effect mobilities in the order of 10–2 cm2 V–1 s–1 in bottom-gate, top-contact organic field-effect transistors (OFETs) suggest an enhancement in charge transport due to the discotic electron-rich pyrene units that help mitigate the insulating effect of the methacrylate backbone. The formation of uniform microdomains of P3HT-b-poly(PyMA) observed with tapping mode atomic force microscopy (TMAFM) on the channel regions of OFETs indicates the unique packing of the block copolymer in comparison to pristine P3HT. Thermotropic properties of the novel discotic mesogen in the presence and absence of P3HT were observed with both the poly(3-hexylthiophene)-b-poly(6-(pyren-1-yloxy)hexyl methacrylate) (P3HT-b-poly(PyMA)) block copolymer and poly(6-(pyren-1-yloxy)hexyl methacrylate) (poly(PyMA)) homopolymer using polarized optical microscopy (POM) and differential scanning calorimetry (DSC).

Ionic Dopant‐Induced Ordering Enhances the Thermoelectric Properties of a Polythiophene‐Based Block Copolymer

AbstractConjugated polymer‐based block copolymers (CP‐BCPs) are an unexplored class of materials for organic thermoelectrics. Herein, the authors report on the electronic conductivity (σ) and Seebeck coefficient (α) of a newly synthesized CP‐BCP, poly(3‐hexylthiophene)‐block‐poly (oligo‐oxyethylene methacrylate) (P3HT‐b‐POEM), upon solution co‐processing with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and subsequently vapor‐doping with a molecular dopant, 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ). It is found that the addition of the hydrophilic block POEM greatly enhances the processability of P3HT, enabling homogeneous solution‐mixing with LiTFSI. Notably, interactions between P3HT‐b‐POEM with ionic species significantly improve molecular order and unexpectedly cause electrical oxidizing doping of P3HT block both in solution and solid‐states, a phenomenon that has not been previously observed in Li‐salt containing P3HT. Vapor doping of P3HT‐b‐POEM‐LiTFSI thin films with F4TCNQ further enhances σ and yields a thermoelectric power factor PF = α2σ of 13.0 µW m−1 K−2, which is more than 20 times higher than salt‐free P3HT‐b‐POEM sample. Through modeling thermoelectric behaviors of P3HT‐b‐POEM with the Kang‐Snyder transport model, the improvement in PF is attributed to higher electronic charge mobility originating from the enhanced molecular ordering of P3HT. The results demonstrate that solution co‐processing CP‐BCPs with a salt is a powerful method to control structure and performance of organic thermoelectric materials.

Core@Corona Functional Nanoparticle-Driven Rod-Coil Diblock Copolymer Self-Assembly.

Herein, a novel strategy to overcome the influence of π-π stacking on the rod-coil copolymer organization is reported. A diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene glycol methyl ether methacrylate) (P3HT-b-PEGMA) was synthesized by the Huisgen cycloaddition, so-called "click chemistry", combining the PEGMA and P3HT blocks synthesized by atom transfer radical polymerization and Kumada catalyst transfer polymerization, respectively. Using a dip-coating process, we controlled the original film organization of the diblock copolymer by the crystallization of the P3HT block via π-π stacking. The morphology of the P3HT-b-PEGMA films was influenced by the incorporation of gold nanoparticles (GNPs) coated by poly(ethylene glycol) ligands. Indeed, the crystalline structuration of the P3HT sequence was counterbalanced by the addition in the film of gold nanoparticles finely localized within the copolymer PEGMA matrix. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry analysis validated the GNP homogeneous localization into the compatible PEGMA phase. Differential scanning calorimetry showed the rod block crystallization disruption. A morphological transition of the self-assembly is observed by atomic force microscopy from P3HT fibrils into out-of-plane cylinders driven by the nanophase segregation.

Influence of the molecular weight in P3HT block on fully conjugated block copolymers

All-conjugated donor-acceptor block copolymers (BCP) were synthesized in a one-pot reaction by a Stille coupling polycondensation through a terminal functional polymer copolymerization process. Mono bromo end-functionalized P3HT samples with various molecular weights (P3HT-Br, Mn: 5, 9, and 26 kg/mol) were copolymerized with AA (N,Nʹ-Bis(2-decyl-1-tetradecyl)-2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic acid bisimide, NDI) and BB (5,5′-bis(trimethylstannyl)-2,2′-bithiophene) type monomers. Further purification by preparative GPC removed excess P3HT to yield block copolymers of low polydispersities with different donor and acceptor block chain lengths. The block copolymers were characterized by 1H-NMR and UV–vis absorption and FTIR spectroscopy. The optical properties, film morphologies, and optoelectronic properties of the block copolymer were strongly influenced by the donor and acceptor block chain lengths. Furthermore, the fully conjugated D-A block copolymer films exhibited fine structures, smooth film morphologies, and better OPV performance than those features of P3HT/PNDIT2 polymer blends. In polymer solar cells based on the various block copolymer as active layers, the device power convention efficiency was improved by maintaining the acceptor block content at 40–50 kg/mol and increasing the P3HT chain from 5 to 26 kg/mol.

Diblock copolymers consisting of a redox polymer block based on a stable radical linked to an electrically conducting polymer block as cathode materials for organic radical batteries

Coupling a conjugated P3HT block to a radical polymer block leads to improved PTMA battery performances.

Modulating Regioregularity of Poly(3-hexylthiophene)-based Amphiphilic Block Copolymers To Control Solution Assembly from Nanowires to Micelles

In selective solvents, poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) assemble into one-dimensional nanowires (NWs) due to strong π–π stacking interactions of the P3HT block. Herein, we report the effect of P3HT regioregularity (RR) on the assembly of P3HT-based amphiphilic BCPs in solution. We synthesized a series of P3HT-block-poly(2-vinylpyridine) (P3HT-b-P2VP) copolymers with similar molecular weights and P3HT volume fractions but with different RRs, ranging from 55% to 95%, and studied their assembly in tetrahydrofuran/n-butanol mixtures. P3HT-b-P2VP copolymers with high RR (>80%) crystallized into well-ordered NWs with core widths consistent with fully extended P3HT chains. In BCP nanostructures with decreasing RR, more flexible P3HT chains produced gradual increases in the width of the NWs, from 12 to 24 nm. Eventually, a morphological transition to spherical micelle structures was observed at 55% RR. The structural differences were visualized by incorporating Au nanoparticles, which l...

Highly enhanced electromechanical properties of PVDF-TrFE/SWCNT nanocomposites using an efficient polymer compatibilizer

PVDF-TrFE/SWCNT nanocomposites with outstanding electromechanical properties were produced using P3HT-PMMA block copolymers as a compatibilizer between PVDF-TrFE and SWCNT. P3HT-PMMA block copolymer coated SWCNT (PTMCNT) was first prepared to utilize π-π stacking interactions between SWCNT and the P3HT block segment. The obtained PTMCNTs are highly compatible with the PVDF-TrFE matrix due to strong hydrogen bonding interaction between the polymer matrix and the PMMA block segment on the surface of SWCNT, leading to a very low percolation behavior at 0.05 wt% of SWCNT in PVDF-TrFE. The obtained electroactive PVDF-TrFE/SWCNT nanocomposites showed ca. 50 times increased electromechanical thickness strain, ca. 3200 times increased elastic energy density, and ca. 460 times increased electrical-to-mechanical energy conversion rate in comparison to those of pristine PVDF-TrFE at the relatively low electric field (50 Vppμm-1). These outstanding properties result from the ultra-low percolation of SWCNT along with uniform local field distribution in PVDF-TrFE, which kept not only intrinsic properties of PVDF-TrFE such as all-trans formed crystalline phase and softness but also enhanced electrical properties including dielectric constant.

Verification of Scherrer formula for well-shaped poly(3-hexylthiophene)-based conductive single crystals and nanofibers and fabrication of photovoltaic devices from thin film coating

Scherrer formula was verified for the single crystals and nanofibers prepared from poly(3-hexylthiophene) (P3HT)-based homopolymers (non-hairy) and block copolymers (hairy) with polystyrene, poly(methyl methacrylate), and poly(ethylene glycol) in toluene, xylene, and anisole. Despite the fact that he single crystals were grown in very thicker dimensions (57-139 nm) compared to the nanofibers (2-8 nm), the data obtained in the hexyl chains direction from atomic force microscopy and grazing wide angle X-ray scattering using Scherrer formula had a high consistency for both hairy and non-hairy single crystals and nanofibers grown from toluene. This adaption was detected only in toluene for the single crystals, however, in toluene and xylene for the nanofibers. In a better solvent employed in the growth environment, both single crystals and nanofibers were composed of lower number of discrete crystallites in their thickness and longitude. The other effective parameters on the crystallite sizes inside the single crystals and nanofibers in both (100) and (020) directions were the crystallization temperature, the molecular weight of rigid P3HT block, and the end coily blocks. The longer P3HT backbones reflected the thinner and shorter crystallites assembled inside the single crystals (25-87 nm in hexyl chains and 48-166 nm in π-π stacking directions) and nanofibers (2-7 nm in hexyl chains and 2-25 nm in π-π stacking directions). Finally, thin films of pre-developed structures were employed as active layers in P3HT:phenyl-C71-butyric acid methyl ester (PC71BM) photovoltaic cells, and the device characteristics were investigated.

High‐Quality Nano/Micro Hairy Single Crystals Developed from Poly(3‐hexylthiophene)‐Based Conductive–Dielectric Block Copolymers Having Flat‐on and Edge‐on Orientations

Highly uniform and conductive single crystals of poly(3‐hexylthiophene) (P3HT)‐based homo and block copolymers with the end coily blocks of polystyrene, poly(methyl methacrylate), and poly(ethylene glycol) are developed using self‐seeding method from varied quality solvents. Edge‐on and flat‐on orientations are detected depending on the thickness and width of single crystals. Coily blocks are excluded from the P3HT crystalline structures, leading to brush‐like or hairy regions on surface of grown single crystals in the longitude of P3HT chains. The larger single crystals possessing flat‐on orientation are obtained from weaker solvents at higher seeding temperatures. The longer P3HT chains are folded, however, the shorter backbones are laminated on each other. The highest backbone lamination occurs for homo‐P3HT7150 (Mn of P3HT = 7150 g mol−1) single crystals grown at 20 °C from anisole, the weakest employed solvent. In contract, highly ordered and folded hairy single crystals are acquired from better solvents and high molecular weight P3HTs. In these conditions, the crystallographic features of the hairy block copolymer single crystals are similar to those of nonhairy homo‐P3HT ones. The coily brush‐covered P3HT48 800 single crystals have more foldings compared to the homo‐P3HT48 800 ones, whereas only two laminated backbones in shorter P3HT blocks are detected. image

Regioregularity-Driven Morphological Transition of Poly(3-hexylthiophene)-Based Block Copolymers

Conjugated polymer-based block copolymers (BCPs) offer great potential to provide beneficial nanostructures for efficient organic optoelectronics. However, their complicated self-assembly behavior, which is attributed to the strong crystallization of conjugated blocks, is still not well understood due to the lack of a model BCP system. Herein, we develop a series of novel conjugated polymer-based BCPs, poly(3-hexylthiophene)-block-poly(2-vinylpyridine) (P3HT-b-P2VP), in which the regioregularity (RR) of the P3HT block was varied from 95 to 73%. The tunable RR content allows for precise regulation of P3HT crystallization with minimal influence on the microphase-separation force between the P3HT and P2VP blocks. When RR is high (i.e., 95 or 85%), structure formation is controlled by crystallization of P3HT, and the ultimate structure is characterized by nanoscale P3HT fibrils in an amorphous matrix. In contrast, as RR decreases to 78 and 73%, P3HT crystallization is suppressed. The self-assembly is controll...

Stretchable Conjugated Rod–Coil Poly(3-hexylthiophene)-block-poly(butyl acrylate) Thin Films for Field Effect Transistor Applications

We report the synthesis, morphology, and properties of poly(3-hexylthiophene)-block-poly(butyl acrylate) (P3HT-b-PBA) for stretchable electronics applications, which are consisted of semiconducting P3HT and low glass transistion temperature (Tg) PBA blocks. The P3HT-b-PBA thin films self-assembled into fibrillar-like nanostructures and maintained the edge-on oreientation even at a low P3HT composition, based on the results from atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). By varying the P3HT/PBA ratio, the tensile modulus decreased as the block length of PBA increased, from 0.93 GPa for P3HT to 0.19 GPa for P3HT-b-PBA12k. The field effect transistor (FET) using P3HT-b-PBA as the active layer exhibited a high p-type mobility over 10–2 cm2 V–1 s–1, indicating its good charge transporting ability. Furthermore, the P3HT-b-PBA6k based FET under 100% strain had a high mobility of 2.5 × 10–2 cm2 V–1 s–1 with an on/off ratio of 7.2 × 106, and it maintained over 10–2 cm2 V–1 s–1 fo...

Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole–terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small-angle X-ray scattering with the P3HT block remaining well-solvated. The nanostructure in thin films was determined using a combination of wide and small-angle X-ray scattering techniques as a function of processing conditions. The structure in solution controlled the initial nanostructure in spin-cast thin films, allowing subsequent thermal annealing processes to further improve the ordering. In contrast to the results for thin films, nanostructural ordering was not observed in the bulk samples by small-angle X-ray scattering. These results suggest the importance of controlling solvent induced aggregation in forming nanostructured th...

Self-assembled block copolymer templates for atomic layer deposition: The effect of processing solvent

In this study thin films of a rod-coil block copolymer (BCP) are deposited from different solvents and used as templates for atomic layer deposition (ALD) of ZnO. The BCP, P3HT-b-PEO, is known to self-organize into fiber-like phase-separated nanostructures, with central crystalline P3HT domains and outer amorphous PEO domains. The P3HT block in this study is short so that the size of the P3HT domains in the films is solvent insensitive. However, processing from poor PEO solvents results in thin PEO domains and good PEO solvents allow extended PEO chains and wide domains. The crystallinity of the P3HT-block and the affinity of the PEO-block to the ALD ZnO precursors lead to selective deposition of ZnO in the PEO domains. Therefore, the solvent-controlled morphology of the PEO domains in the BCP films can be translated to the size, distribution and morphology of the deposited ZnO. We show that films with swollen PEO domains have higher ZnO uptake compared to films with collapsed PEO chains. Furthermore, oriented PEO domains template oriented ZnO domains and wormlike morphologies direct wormlike ZnO nanostructures. Therefore, solvent selection is a toll to manipulate the BCP self-assembly and hence the ALD template and the morphology of the hybrid organic/inorganic film.

Improved performance and stability of inverted polymer solar cells with ammonium heptamolybdate acted as hole extraction layers via thermal annealing method

High-performance Inverted polymer solar cells (PSC) were fabricated with ammonium heptamolybdate (NH4)6Mo7O24−4H2O as hole extraction layer (HEL), and the blend of the poly(3-hexylthiophene) (P3HT):indene-C60 bisadduct (ICBA) as photoactive layer, using the structure of ITO/ZnO/P3HT:ICBA/(NH4)6Mo7O24/Ag. Correspondingly, the influence of different annealing time of ammonium heptamolybdate on carrier mobility and thus device performance were investigated. The power conversion efficiency (PCE) has been optimized from 4.12% to 6.24% after thermal annealing treatment of (NH4)6Mo7O24 layer at 130 °C for 15min. The results of ultraviolet photoelectron spectroscopy (UPS) curve clearly proven the increase of conduction-band minimum (CBM) and valence-band maximum (VBM) energy level of (NH4)6Mo7O24 layer upon thermal annealing, which is caused by the decrease of barrier potential between HOMO of P3HT and HEL. This obviously facilitate hole transport hole transport between HOMO levels of P3HT and HEL block electron transfer between LUMO levels of P3HT and Ag electrode. The space charge-limited current (SCLC) test has further confirmed the enhanced hole collection and transport capability of (NH4)6Mo7O24 after thermal annealing treatment.

Enhancing Long-Range Ordering of P3HT by Incorporating Thermotropic Biphenyl Mesogens via ATRP

The methoxybiphenyl liquid crystalline mesogen 6-((4′-methoxy-[1,1′-biphenyl]-4-yl)oxy)hexyl methacrylate (MeOBP) was incorporated into block copolymers with regioregular poly(3-hexylthiophene) (P3HT) by a combination of Grignard metathesis (GRIM) and atom transfer radical polymerization (ATRP) techniques. Side chain engineering with a thermotropic liquid crystalline segment produced an improved morphology resulting in field-effect mobilities of ∼10–2 cm2/(V s) measured in organic thin film transistors (OTFTs). It was observed that improved π–π stacking distances between edge-on oriented polythiophene segments upon annealing facilitated charge transport which was accomplished with π–π stacked biphenyl mesogens with P3HT block. Variation of surface morphology of polymer thin films upon annealing was investigated by tapping mode atomic force microscopy (TMAFM). A combined study of differential scanning calorimetry (DSC) and polarized optical microscopy (POM) was also performed to identify liquid crystalline...

Influence of Composition of Amphiphilic Double-Crystalline P3HT-b-PEG Block Copolymers on Structure Formation in Aqueous Solution

A series of poly(3-hexylthiophene)-block-poly(ethylene glycol) (P3HT-b-PEG) with constant P3HT block length block and variable PEG block lengths are presented. Alkyne-functionalized P3HT with high absolute molecular weight of 11.4 kg/mol is combined with azide-functionalized PEGs via copper-catalyzed alkyne–azide cycloaddition (CuAAC). The resulting P3HT-b-PEG block copolymers have PEG weight fractions between 15 and 64 wt %. In bulk materials the crystallinity in the conjugated block is similar to pure P3HT, while the crystallinity of PEG is influenced with decreasing PEG block length. On addition of MeOH as a nonsolvent for the P3HT block, these block copolymers are able to form stable micellar aggregates if the PEG fraction is >31 wt %. In AFM, DLS, and cryo-TEM, P3HT-b-PEG micelles are found to have a spherical or cylindrical shape with diameters of around 25 nm and lengths between 40 nm and some hundred nanometers. It is found that short PEG blocks lead to bigger block copolymer micelles. Thus, a cor...

All-conjugated donor–acceptor graft/block copolymers as single active components and surfactants in all-polymer solar cells

In this work, we report the synthesis of all-conjugated donor---acceptor (D---A) graft/block copolymers via an externally-initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, end-functional electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized via KCTP initiated by the Ni(COD)2-activated PNDI complexes. Therefore, a series of D---A graft copolymers and ABA-type (P3HTs were initiated from both ends of PNDI) triblock copolymers were successfully synthesized. The polymers were used to fabricate polymer thin film transistors and the results indicated that all the polymers exhibited moderate charge mobilities ranging from 10ź4 to 10ź3 cm2 Vź1 sź1, and they could be further improved by thermal annealing. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active components or as surfactants. A power conversion efficiency (PCE) of 0.22 % with open circuit voltage (Voc) = 0.55 V, short circuit current density (Jsc) = 0.64 mA/cm2, and fill factor (FF) = 0.62 was recorded by using the donor---acceptor all-conjugated block copolymer as acceptor, and a PCE of 2.28 % with Voc = 0.61 V, Jsc = 7.00 mA/cm2, and FF = 0.54 was obtained when PNDI was used as a surfactant.

Crystallization assisted microphase separation in all-conjugated phenylene-thiophene diblock copolymers

We demonstrated the crystallization assisted microphase separation of all-conjugated diblock copolymers poly (2,5-dihexyloxy-p-phenylene)-block-(3-hexylthiophene) (PPP-b-P3HT, denoted as BmTn). The crystallization and microphase separation are summarized in terms of the difference of aggregation in solvent and the crystallization temperatures of two blocks, respectively. B39T18 and B41T44 were selected, and crystalline nanowires were formed for B39T18 cast from non-selective solvent via the crystallization of PPP block overwhelming P3HT block. However, both microphase separation and crystallization occurred from selective solvent for PPP block, due to the enhanced aggregation of P3HT block governed by solvophobic interactions. The morphological evolution of B41T44 with equivalent crystallization capacity displayed an opposite result. The lamellar nanostructures formed in films were cast from non-selective solvent and the crystallization breakout microphase separation was formed from selective solvent. Besides, the evolution and phase transition in the thermal annealing process indicated that the PPP crystallized confined from the molten in the P3HT crystalline region, and then the P3HT breakout crystallized primarily and microphase separation with the molten PPP occurred.

Donor–Acceptor Poly(3‐hexylthiophene)‐block‐Pendent Poly(isoindigo) with Dual Roles of Charge Transporting and Storage Layer for High‐Performance Transistor‐Type Memory Applications

Field‐effect transistor memories usually require one additional charge storage layer between the gate contact and organic semiconductor channel. To avoid such complication, new donor–acceptor rod–coil diblock copolymers (P3HT44‐b‐Pison) of poly(3‐hexylthiophene) (P3HT)‐block‐poly(pendent isoindigo) (Piso) are designed, which exhibit high performance transistor memory characteristics without additional charge storage layer. The P3HT and Piso blocks are acted as the charge transporting and storage elements, respectively. The prepared P3HT44‐b‐Pison can be self‐assembled into fibrillar‐like nanostructures after the thermal annealing process, confirmed by atomic force microscopy and grazing‐incidence X‐ray diffraction. The lowest‐unoccupied molecular orbital levels of the studied polymers are significantly lowered as the block length of Piso increases, leading to a stronger electron affinity as well as charge storage capability. The field‐effect transistors (FETs) fabricated from P3HT44‐b‐Pison possess p‐type mobilities up to 4.56 × 10−2 cm2 V−1 s−1, similar to that of the regioregular P3HT. More interestingly, the FET memory devices fabricated from P3HT44‐b‐Pison exhibit a memory window ranging from 26 to 79 V by manipulating the block length of Piso, and showed stable long‐term data endurance. The results suggest that the FET characteristics and data storage capability can be effectively tuned simultaneously through donor/acceptor ratio and thin film morphology in the block copolymer system.

Importance of choosing the right polymerization method for in situ preparation of semiconducting nanoparticles from the P3HT block copolymer

Precise control on synthesis of P3HT-b-PT at the molecular level promotes more controlled in situ nanoparticlization to give more well-defined nanostructures.