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

Controlling the morphology and crystallization of a thiophene-based all-conjugated diblock copolymer by solvent blending

We report the crystallization and microphase separation behavior of an all-conjugated poly(3-hexylthiophene)-b-poly[3-(6-hydroxy)hexylthiophene] (P3HT-b-P3HHT) block copolymer in mixed solvents and demonstrate how the conformations of P3HT and P3HHT chains influence the photophysical properties of the copolymer. It is shown that the balance among π-π stacking of P3HT, P3HHT and microphase separation of the copolymer can be dynamically shifted by controlling the rod-rod interactions of the copolymer via changing the block ratio and solvent blending. A series of nanostructures such as well-ordered nanofibers, spheres and lamellar structures are formed and their formation mechanisms and kinetics are discussed in detail. The variations in P3HT-b-P3HHT conformations are concomitant with 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 demonstrates how the P3HT-b-P3HHT conformations crystallize and phase-separate in the solution and solid state, and the correlation between their structures and photophysical properties, which improves our understanding of all-conjugated rod-rod block copolymer systems.

Synthetic approaches towards structurally-defined electrochemically and (photo)redox-active polymer architectures

This review details synthetic strategies leading to structurally-defined electrochemically and (photo)redox-active polymer architectures,e.g.block, graft and end functionalized (co)polymers.

Core/Shell Conjugated Polymer/Quantum Dot Composite Nanofibers through Orthogonal Non-Covalent Interactions

Nanostructuring organic polymers and organic/inorganic hybrid materials and controlling blend morphologies at the molecular level are the prerequisites for modern electronic devices including biological sensors, light emitting diodes, memory devices and solar cells. To achieve all-around high performance, multiple organic and inorganic entities, each designed for specific functions, are commonly incorporated into a single device. Accurate arrangement of these components is a crucial goal in order to achieve the overall synergistic effects. We describe here a facile methodology of nanostructuring conjugated polymers and inorganic quantum dots into well-ordered core/shell composite nanofibers through cooperation of several orthogonal non-covalent interactions including conjugated polymer crystallization, block copolymer self-assembly and coordination interactions. Our methods provide precise control on the spatial arrangements among the various building blocks that are otherwise incompatible with one another, and should find applications in modern organic electronic devices such as solar cells.

Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties

The microstructure of the active blend layer has been shown to be a critically important factor in the performance of organic solar devices. Block copolymers provide a potentially interesting avenue for controlling this active layer microstructure in solar cell blends. Here we explore the impact of backbone fluorination in block copolymers of poly(3-octyl-4-fluorothiophene)s and poly(3-octylthiophene) (F-P3OT-b-P3OT). Two block co-polymers with varying block lengths were prepared via sequential monomer addition under Kumada catalyst transfer polymerisation (KCTP) conditions. We compare the behavior of the block copolymer to that of the corresponding homopolymer blends. In both types of system, we find the fluorinated segments tend to dominate the UV-visible absorption and molecular vibrational spectral features, as well as the thermal behavior. In the block copolymer case, non-fluorinated segments appear to slightly frustrate the aggregation of the more fluorinated block. However, in situ temperature dependent Raman spectroscopy shows that the intramolecular order is more thermally stable in the block copolymer than in the corresponding blend, suggesting that such materials may be interesting for enhanced thermal stability of organic photovoltaic active layers based on similar systems.

Nano-structuring polymer/fullerene composites through the interplay of conjugated polymer crystallization, block copolymer self-assembly and complementary hydrogen bonding interactions

Core–shell P3HT/fullerene composite nanofibers were obtained using supramolecular chemistry involving cooperative orthogonal non-covalent interactions.

Architectural engineering of rod-coil compatibilizers for producing mechanically and thermally stable polymer solar cells

While most high-efficiency polymer solar cells (PSCs) are made of bulk heterojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they have a significant morphological instability issue against mechanical and thermal stress. Herein, we developed an architecturally engineered compatibilizer, poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP), that effectively modifies the sharp interface of a BHJ layer composed of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs was successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-g-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-g-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-b-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as supported by molecular dynamics simulations.

Cooperative assembly of pyrene-functionalized donor/acceptor blend for ordered nanomorphology by intermolecular noncovalent π-π interactions

A facile approach to develop the stable and well-defined bulk heterojunction (BHJ) nanomorphology has been demonstrated. Novel pyrene (Py)-functionalized diblock copolymers poly(3-hexylthiophene)-block-poly[3-(10-(pyren-1-yloxy)decyloxy)thiophene] (P3HT-b-P3TPy), and pyrene-functionalized fullerene [6,6]-phenyl-C61-butyric acid 1-pyrene butyl ester (PCBPy), were successfully synthesized. The π-π interactions of Py mesogens interdigitated between the functionalized fullerene and P3TPy segment can allow for the cooperative assembly of P3HT-b-P3TPy and PCBPy. The orientation of the Py mesogens also can further enhance the molecular arrangement. Compared with the as-cast and thermal annealing, solvent annealing can promote cooperative assembly of P3HT-b-P3TPy:PCBPy undergoing the slow film growth. Note that the assembly microstructure strongly depends on the molar ratio of P3HT and P3TPy with Py mesogens. Low loading of P3TPy block in the copolymers blends keeps the same behavior to the P3HT, whereas relatively high loading of Py mesogens favors the better intermolecular π-π stacking interactions between P3HT-b-P3TPy and PCBPy. As a result, the P3HT-b-P3TPy(3/1) forms the orientated nanowires with PCBPy in bulk heterojunction, and the average domain size is estimated to be 10-20 nm, which is desirable for enlarge surface area for donor/acceptor interfaces and give a bicontinuous pathway for efficient electron transfer. Furthermore, the cooperative assembly between P3HT-b-P3TPy and PCBPy is found to effectively suppress the PCBPy macrophase separation, and stabilize the blend morphology.

Dithienosilole-based all-conjugated block copolymers synthesized by a combination of quasi-living Kumada and Negishi catalyst-transfer polycondensations

The synthesis of diblock copolymers containing poly(dithieno[3,2-b:2’,3’-d]silole) and poly(3-hexylthiopnene) blocks was accomplished by a combination of quasi-living Kumada and Negishi catalyst-transfer polycondensations.