Organic electronics is a rising field, with novel applications including but not limited to stretchable solar cells, flexible display screens, and biosensors. The high performance of these organic ...electronics is enabled by the outstanding optoelectronic and thermomechanical features of organic semiconducting materials. However, the production of the promising organic semiconducting materials at industrial scales has not yet become feasible, due to huge energy and capital costs in the large-scale synthesis as well as the potential damage to the environment and human health caused by vast hazardous chemical waste released. This review summarizes recent research advances in improving the environmental friendliness of the organic semiconducting material synthesis by appying atom economical C-H functionalization-based synthetic routes, minimizing hazardous chemical waste, lowering the energy consumption, and employing safe and abundant chemicals including naturally sourced semiconducting building blocks. This review showcases the remarkable progress that has been made towards the environmentally friendly organic semiconductor synthesis and provides insight for researchers developing green synthetic strategies and organic semiconductor building blocks in the future.
This review presents the recent advances in the synthesis of organic semiconductors using C-H functionalization and naturally sourced building blocks to facilitate the large-scale production and commercialization of organic semiconductors.
A series of alkyl-substituted indacenodithiophene (alkyl-IDT) semiconducting donor–acceptor polymers were designed by DFT to have varying degrees of backbone planarity and synthesized via direct ...arylation polymerization (DArP). These polymers exhibit weak intermolecular interactions, a glass transition temperature (T g) below room temperature, and low degrees of crystallinity from XRD measurements. Despite this, the field-effect mobilities (μ) of these polymers are relatively high (0.06–0.20 cm2 V–1 s–1) with mobility increasing with increasing backbone planarity. Because of the weak intermolecular interactions, the polymers exhibit low elastic moduli (E f) of less than 450 MPa. The polymer with the most twisted backbone exhibits high ductility with a crack-onset strain (CoS) over 100%. These structure–property relationship studies provide useful guidelines for designing semiconducting polymers with high mobility, low stiffness, and high ductility enabling applications in stretchable electronics.
In 2018, several major breakthroughs have been achieved in organic solar cells (OSCs) with the record power conversion efficiency (PCE) reaching over 17 %. With this increased efficiency, it is time ...to take a step forward to consider how to convert this technology into large scale production. For this, the economic and environmental profile of OSCs should be taken seriously‐simplified synthetic routes and green chemistry methods should be applied. According to previous studies, OSCs are competitive and profitable in the commercial market. However, toxic and/or hazardous chemicals are currently used in materials synthesis and device fabrication of OSCs. In this account, we will talk about contributions and efforts we have made to minimize the economic and environmental disadvantages in the production of OSCs. We will start with the background on how our projects were conceived and will specifically discuss our work on direct arylation and green solvent. Developments of direct arylation for synthesizing conjugated polymers will be illustrated along with our recent finding regarding the effect of green solvents on device performance and stability.
As a green energy solution, organic solar cells have attracted world‐wide attention in past decades. With power conversion efficiency records as high as 17 %, its industrial profile should be now taken into perspective. In this account, we will share our thinking and research regarding different aspects on the industrialization of organic solar cells, such as economic and environmental profiles, and polymer synthesis and device fabrication optimization
The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce ...2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F4TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F4TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm2 V−1 s−1 in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.
This study sequentially dopes conjugated polymer films with controlled crystallinity, finding that dopants do not π‐stack with the polymer chains. The most crystalline films show the highest carrier mobilities and a redshifted absorption with increased cross section due to enhanced polaron delocalization.
Conjugated polymers have been under active development since the 1970s as the active material in organic field-effect transistors (OFETs), photovoltaic devices and the emissive layer in ...light-emitting diodes (LEDs). Extensive work has been performed to investigate the physics and chemistry of these materials, and a variety of semiconducting polymers have been synthesized using a range of polymerization techniques. One of the most important key technologies is to obtain a well-controlled polymerization, which provides polymers with narrow polydispersities and defined molecular weights. In this paper, we describe the recent progress on the synthesis of semiconducting polymers as classified as polyphenylenes, polyphenylenevinylenes, polythiophenes, polyfluorene and their block copolymers by the use of controlled polymerizations.
The Carothers equation is often used to predict the utility of a small molecule reaction in a polymerization. In this study, we present the mechanistic study of Pd/Ag cocatalyzed cross ...dehydrogenative coupling (CDC) polymerization to synthesize a donor–acceptor (D–A) polymer of 3,3′-dihexyl-2,2′-bithiophene and 2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl, which go counter to the Carothers equation. It is uncovered that the second chain extension cross-coupling proceeds much more efficiently than the first cross-coupling and the homocoupling side reaction (at least 1 order of magnitude faster) leading to unexpectedly low homocoupling defects and high molecular weight polymers. Kinetic analyses show that C–H bond activation is rate-determining in the first cross-coupling but not in the second cross-coupling. Based on DFT calculations, the high cross-coupling rate in the second cross-coupling was ascribed to the strong Pd-thiophene interaction in the Pd-mediated C–H bond activation transition state, which decreases the energy barrier of the Pd-mediated C–H bond activation. These results have implications beyond polymerizations and can be used to ease the synthesis of a wide range of molecules where C–H bond activation may be the limiting factor.
The field of stretchable electronics has recently gained significant interest from the academic community, with a focus on producing materials that demonstrate reliable electrical performance with ...improved response to mechanical deformation. This review highlights the recent progress in understanding the relationships between the mechanical behavior and electrical performance of such devices. Potential solutions can take the form of intrinsically elastic polymers, polymer semiconductor/elastomer blends and alternative engineering-oriented approaches, which are discussed herein. Trends and design strategies are beginning to manifest in this early stage of the stretchable electronics field. The development of stretchable electrical systems can provide unique applications of organic electronics.
Polythiophenes are one of the most widely studied conjugated polymers. With the discovery of the chain mechanism of Kumada catalyst-transfer polymerisation (KCTP), various polythiophene copolymer ...structures, such as random, block, and gradient copolymers, have been synthesized
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batch or semi-batch (sequential addition) methods. However, the lack of quantitative kinetic data for thiophene monomers brings challenges to experimental design and structure prediction when synthesizing the copolymers. In this study, the reactivity ratios and the polymerisation rate constants of 3-hexylthiophene with 4 thiophene comonomers in KCTP are measured by adapting the Mayo-Lewis equation and the first-order kinetic behaviour of chain polymerisation. The obtained kinetic information highlights the impact of the monomer structure on the reactivity in the copolymerisations. The kinetic data are used to predict the copolymer structure of equimolar batch copolymerisations of the 4 thiophene derivatives with 3-hexylthiophene, with the experimental data agreeing well with the predictions. 3-Dodecylthiophene and 3-(6-bromo)hexylthiophene, which have higher structural similarity to 3-hexylthiophene, show nearly equivalent reactivity to 3-hexylthiophene and give random copolymers in the batch copolymerisation. 3-(2-Ethylhexyl)thiophene with a branched side chain is less reactive compared to 3-hexylthiophene and failed to homopolymerize at room temperature, but produced gradient copolymers with 3-hexylthiophene. Finally, the bulkiest 3-(4-octylphenyl)thiophene, despite its ability to homopolymerize, failed to maintain chain polymerisation in the copolymerisation with 3-hexylthiophene, possibly due to the large steric hindrance caused by the phenyl ring directly attached to the thiophene center. This study highlights the importance of monomer structures in copolymerisations and the need for accurate kinetic data.
This work explores how various polythiophenes copolymers can be synthesized
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Kumada catalyst transfer polymerisation, demonstrating that the accurate kinetic measurements of thiophene monomers enable reliable predictions of copolymer structures.
Direct arylation polymerization (DArP) has gained interest in materials chemistry as a method to synthesize conjugated polymers with minimal use of harsh reagents and additional steps. Traditional ...DArP conditions do not readily yield ideal polymerization characteristics, including chain-growth and low dispersities. It would be of great utility to advance DArP methodology to become competitive with traditional conjugated polymerization techniques. We have developed conditions for a dual-catalytic Ag–Pd system for the synthesis of poly(3-hexylthiophene) (P3HT) that exhibits chain-growth kinetics, low dispersities, and catalyst chain association by Pd. Specifically, the presence of Ag-carboxylate additives plays a beneficial role in the polymerization as a C–H activating agent, while PEPPSI-iPr is used as the Pd source for C–C coupling. The addition of pyridine is necessary to inhibit Pd-mediated C–H activation in the interest of catalyst orthogonality, which can lower dispersities.
π-Conjugated small molecules, oligomers, and macromolecules are being used in the fabrication of a wide variety of organic electronic devices such as organic field-effect transistors (OFETs), organic ...photovoltaic (OPV) devices, and organic light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compounds are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Additionally, synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon–hydrogen bond activation and subsequent carbon–carbon bond formation (C–H functionalization). While the C–H functionalizations represented by direct arylation-based methods are not as developed as the widely used Stille and Suzuki methods at this stage, they allow for the use of readily accessible halogenated aromatic substances and can negate the need for toxic organotin reagents. They also hold promise of allowing for the synthesis of previously inaccessible materials. In this Perspective, our goal is to provide an overview of the current status in this challenging field by highlighting (1) the history of preparing π-conjugated small molecules and macromolecules via cross-coupling reactions, (2) advances in preparation of versatile π-conjugated small molecules and macromolecules via transition-metal-catalyzed direct arylation, and (3) the scope, limitations, and challenges for materials science.
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