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Conjugated polymers based on 2,6-azulene have been synthesized and their electronic and optical properties characterized. Two of them showed the ability to disperse single-walled carbon nanotubes (SWNTs).

The energetic disorder can be reduced by developing new photovoltaic materials, especially non-fullerene acceptors, and significant progress in the PCEs of OSCs has been made.

In this article, a new series of conjugated polymers based on a low-cost, easily accessible vat dye called Vat orange 1 or 2,9-dibromo-dibenzo[b,def]chrysene-7,14-dione have been prepared. This compound was made electron-donating by reducing and alkylating the ketone groups into alkoxy groups, allowing the introduction of solubilizing, branched alkyl chains at the 7 and 14 positions. Polymerization reactions using Suzuki–Miyaura coupling with 6,6′-isoindigo, 3,6-di-2-thienyl-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) and 4,7-dithieno-2,1,3-benzothiadiazole (TBT) yielded three donor–acceptor polymers with bandgap values ranging from 1.61 to 1.86 eV. Field-effect transistors (OFETs) and organic solar cells (OSCs) were fabricated and hole mobility values of up to 3.62 × 10−4 cm2 V−1 s−1 and a maximum power conversion efficiency of 1.2% were measured, respectively.

Great progress in organic solar cells (OSCs) has been recently achieved owing to the advent of non-fullerene acceptors (NFAs). Indeed, low-bandgap NFAs ranging from 1.3 to 1.6 eV with broad absorpt...

Capturing and converting solar energy into fuels and feedstocks is a global challenge that spans numerous disciplines and fields of research. Billions of years of evolution have allowed natural organisms to hone strategies for harvesting light from the sun and storing energy in the form of carbon–carbon and carbon–hydrogen bonds. Photosynthetic antenna proteins capture solar photons and funnel photoexcitations to reaction centres with high yields, and enzymes catalyze multi-electron reactions, facilitating chemical transformations not yet efficiently implemented using artificially engineered catalysts. Researchers in renewable energy often look to nature to understand the mechanisms at work and, if possible, to explore their translation into artificial systems. Here, we review advances in bioinspiration across the fields of biological light harvesting and chemical energy conversion. We examine how multi-photon and multi-electron reactions in biology can inspire new methods in photoredox chemistry to achieve novel, selective and complex organic transformations; how carbonic-dehydrogenase-inspired design principles enable catalytic reactions such as the conversion of CO2 into useful products such as fuels; and how concepts from photosynthetic antenna complexes and reaction centres can benefit artificial light-harvesting materials. We then consider areas in which bioinspiration could enable advances in the rational design of molecules and materials, the expansion of the synthetic capabilities of catalysts and the valorization of molecular building blocks. We highlight the challenges that must be overcome to realize these advances and propose new directions that may use bioinspiration to achieve them. Natural photosynthetic systems harvest light to perform selective chemistry on atmospheric molecules such as CO2. This Review discusses the implementation of bioinspired concepts in engineered light harvesting and catalysis.

Organic photovoltaics have attracted much attention in the past few years, mainly due to their ability to be fully printed at low cost and large scale. However, the organic semiconductors utilized ...

Power conversion efficiencies (PCEs) of solution-processed organic solar cells (OSCs) have recently reached 17.4% (certified) for single-junction devices. Crucial to this advancement is the development of non-fullerene acceptors (NFAs) since 2015. The recent A-DAD-A NFAs have attracted widespread attention because of their ladder-type electron-deficient-core-based central fused ring with improved transport properties and optimum energy levels. With the synergistic effect of electron-deficient-core and specific molecular geometry, the A-DADA molecules could achieve low voltage losses and high current generation at the same time, reaching new regimes of device physics and photophysics. This perspective will discuss the voltage losses in state-of-the-art A-DAD-A NFA-based OSCs and propose new molecular design strategies to achieve PCEs over 20% in OSCs based on these new acceptors by further decreasing their total voltage losses. Funding Agencies|National Natural Science Foundation of China (NSFC)National Natural Science Foundation of China (NSFC) [21875286]; National Key Research & Development Projects of China [2017YFA0206600]; Science Fund for Distinguished Young Scholars of Hunan ProvinceNational Natural Science Foundation of China (NSFC)National Science Fund for Distinguished Young Scholars [2017JJ1029]; Swedish Research Council VRSwedish Research Council [2018-06048]; Swedish Energy Agency EnergimyndighetenSwedish Energy Agency [2016-010174]; Stiftelsen For Strategisk Forskning through a Future Research Leader program [FFL18-0322]; NSERCNatural Sciences and Engineering Research Council of Canada

Since the world-record power conversion efficiency of 15.7% was achieved for organic solar cells (OSCs) in 2019, the newly developed non-fullerene acceptor (NFA) Y6 with an A-DA′D-A structure (A denotes an electron-accepting moiety, D denotes an electron-donating moiety) has attracted increasing attention. Subsequently, many new A-DA′D-A NFAs have been designed and synthesized, and the A-DA′D-A NFAs have played a significant role in the development of high-performance non-fullerene organic solar cells (NF-OSCs). Compared with the classical A-D-A-type acceptors, A-DA′D-A NFAs contain an electron-deficient core (such as benzothiadiazole (BT), benzotriazole (BTA), quinoxaline (Qx), or their derivatives) in the ladder-type fused rings to fine-tune the energy levels, broaden light absorption and achieve higher electron mobility of the NFAs. This review emphasizes the recent progress on these emerging A-DA′D-A (including Y-series) NFAs. The synthetic methods of DA′D-fused rings are introduced. The relationships between the chemical structure of the A-DA′D-A NFAs and the photovoltaic performance of the corresponding OSCs are summarized and discussed. Finally, issues and prospects for further improving photovoltaic performance of the OSCs are also proposed.

Direct (hetero)arylation polymerization (DHAP) shows great promise for simple, cheap, and environmentally benign preparation of conjugated polymers, but seems to involve a lack of selectivity when different aromatic C–H bonds are present. We report that some time-controlled DHAP reactions can yield well-defined and processable semiconducting polymers. Following these procedures, various aromatic compounds have been efficiently polymerized, including 2,7-dibromofluorene, 2,7-dibromocarbazole, 1,4-dibromobenzene, bithiophene, dithienyl-benzothiadiazole, and diketopyrrolopyrrole derivatives. All resulting polymers have shown comparable, if not slightly better, properties than their Stille- and Suzuki-synthesized analogs. These findings (re)open the door for the low-cost production of many conjugated polymers for plastic electronics.

Polythiophenes comprise a class of emerging materials with potential applications in the field of temperature sensing. In this article, we validate and apply an integrated blending and printing methodology to combinatorially study libraries of pristine and compositionally graded blends of polythiophenes PEDOT:PSS and P(S-EDOT) (a PEDOT-like self-doped conjugated polymer) to understand their intrinsic electrical conductivity behaviour and along with its temperature dependence on blend composition and ambient temperature. Hypothesis testing is conducted to identify optima in electrical conductivity from combinations of input material proportions intended to meet multiple requirements otherwise difficult to achieve in any single-component solution-processable material. We chose PEDOT:PSS as a commercial developed intrinsically conductive polythiophene and with it, compared a novel self-doped polythiophene P(S-EDOT) as its potential replacement or complement as a sensor material. The electrical and morphological characteristics for both polymers and their blends were investigated for use as different components of temperature sensing applications. Different error sources within the process flow were considered for statistically significant conclusions regarding the utility of different compositions for different aspects of temperature sensing.

Forest biomass is viewed as a significant source of organic carbon and thus the ideal replacement of petroleum products. From the resources derived from biomass, lignocellulose is the most abundant biobased material on earth. One of the aromatic added value compounds obtained from the depolymerization of lignin is vanillin. Here, we report the preparation of new compounds having benzothiophene, indole, isatin, benzofuroxan, benzofurazan, benzothiadiazole, and phthalimide heteroaromatic ring structures. More precisely, our results show that vanillin can be used as a biosourced starting material for the preparation of a variety of aromatic dibrominated monomers. X-ray crystallography on single crystals was also performed to obtain meaningful information on their solid-state ordering. This work opens the way to new, sustainable, biosourced aromatic materials (small molecules or polymers) for organic electronics.

Diketopyrrolopyrrole-based (DPP-based) polymers are a very important class of materials for both organic solar cells (OSCs) and organic field-effect transistors (OFETs). Here we report an optimised synthesis of fluorinated dithienyl-diketopyrrolopyrrole (fDT-DPP) and three new highly fluorinated fDT-DPP-based materials obtained from direct heteroarylation polymerization (DHAP). This study confirms the properties of the fluorine atom in a polymer, activation of the α-position hydrogen on thiophene moieties, decreasing HOMO and LUMO energy, lower bandgaps and modification of the solubility and morphology of the materials.

Understanding the influence of polymer molecular weight on the morphology, photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization of the materials and devices for large scale applications. We have synthesized six number-average molecular weight (Mn) values (21–127 kDa) of biselenophene–naphthalenediimide copolymer (PNDIBS) via direct heteroarylation polymerization and used them to investigate the effects of the acceptor polymer molecular weight on the charge transport, blend photophysics, blend morphology, and photovoltaic properties of all-polymer solar cells (all-PSCs) based on PNDIBS and the donor polymer PBDB-T. The short-circuit current and power conversion efficiency (PCE) of the PBDB-T:PNDIBS blend devices were found to increase with increasing Mn until reaching peaks at an optimal molecular weight of 55 kDa and then decreased with further increases in Mn. The maximum PCE of 10.2% observed at the optimal Mn value of 55 kDa coincided with optimal blend charge transport properties, blend photophysics, and blend morphology at this critical molecular weight. Compared to the bi-continuous network of ∼5.5–6.5 nm crystalline domains with predominantly face-on molecular orientations observed at 55 kDa, a relatively disordered microstructure with larger scale phase separation was evident at higher Mn while more finely packed crystalline domains were seen at 21 kDa. The sensitivity of the device efficiency to the active layer thickness was found to also depend on the PNDIBSMn value. These results highlight the importance of tuning the molecular weight of the polymer components to optimize the morphology, charge transport, photophysics and efficiency of all-polymer solar cells. The results also provide new insights on structure–property relationships for a promising n-type semiconducting copolymer.

A π-conjugated copolymer based on a pyrene diimide unit (P(PyDI-T2)) was synthesized using the Suzuki–Miyaura cross-coupling reaction between 4,5,9,10-pyrene diimide-2,7-diboronic ester and 2,2′-di...

In a very short time, direct (hetero)arylation polymerization (DHAP) has established itself as a valuable and atom-economical alternative to traditional cross-coupling methods such as the Migita–Stille and Suzuki-Miyaura polymerizations for the synthesis of low cost and efficient conjugated polymers for organic electronics. Because of sustained research efforts combining in-depth theoretical calculations, the development of new ligands and the careful fine-tuning of polymerization conditions, selectivity and reactivity issues should be soon a thing of the past. This focus review highlights the recent advances that lead to defect-free polymeric semiconductors and conductors and the current limitations and challenges of DHAP as it moves toward simultaneously becoming an industrially feasible, environmentally friendly, and synthetically powerful polymerization technique. The implementation of Direct Heteroarylation Polymerization (DHAP) in the synthesis of well-defined and defect-free materials for organic electronics is still in its early stages but giant leaps have been made over the past few years to improve and stir the selectivity of the reaction to avoid unwanted side-reaction such as β-branching or homocoupling. DHAP has proven to be an efficient, cost-effective, green and scalable polymerization method now competing or even surpassing well-established Suzuki-Miyaura or Migita–Stille cross-coupling polymerization methods. This focus review puts emphasis on the synthetic strategies that made DHAP successful.

Summary Recently, non-fullerene n-type organic semiconductors have attracted significant attention as acceptors in organic photovoltaics (OPVs) due to their great potential to realize high-power conversion efficiencies. The rational design of the central fused ring unit of these acceptor molecules is crucial to maximize device performance. Here, we report a new class of non-fullerene acceptor, Y6, that employs a ladder-type electron-deficient-core-based central fused ring (dithienothiophen[3.2-b]- pyrrolobenzothiadiazole) with a benzothiadiazole (BT) core to fine-tune its absorption and electron affinity. OPVs made from Y6 in conventional and inverted architectures each exhibited a high efficiency of 15.7%, measured in two separate labs. Inverted device structures were certified at Enli Tech Laboratory demonstrated an efficiency of 14.9%. We further observed that the Y6-based devices maintain a high efficiency of 13.6% with an active layer thickness of 300 nm. The electron-deficient-core-based fused ring reported in this work opens a new door in the molecular design of high-performance acceptors for OPVs.

The printing of an efficient thermistor temperature sensor by using self-doped conducting polymers has been achieved. The use of a water-soluble polymer as the active material allows printing and processing in green solvents. The sensor showed a good sensitivity to temperature variations, with a temperature coefficient of resistance of −1.3%. The sensor also exhibited a better stability and reversibility towards humidity compared to the state-of-the-art poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS).

A computational study of the direct arylation reaction was undertaken to understand the origin of nonselective β-couplings observed in thiophene-based polymers prepared by direct (hetero)arylation polymerization (DHAP). The reactivities and selectivities of C–H bond activations were studied for the concerted metalation–deprotonation mechanism on model thiophene substrates using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster with singles, doubles, and perturbative triples (DLPNO-CCSD(T)). Substituent effects are shown to control experimentally observed regioselectivities. Electron-rich or -deficient thiophene substrates with multiple C–H bonds possess an intrinsic selectivity for bond activation at the α-position, while halogens in the α-position substantially reduce coupling selectivities by activating the adjacent Cβ–H bonds. Therefore, the halogenated monomer is responsible for the reported poor selectivities in DHAP. The effect of the substrate undergoing ox...

Organic molecules are emerging candidates for the next generation of cost-effective active materials of Li-ion batteries. Small diimide building blocks such as pyromellitic diimide (PMDI) have attracted much attention because of their high theoretical capacity. Many strategies have been undertaken to limit the well-known phenomenon of dissolution of the active material in the electrolyte. Such strategies include the preparation of salts and the synthesis of polyimides or macrocycles. Since dibromopyromellitic dimiide exhibits almost no sp2 cross-coupling polymerization reaction by conventional synthetic routes (Suzuki–Miyaura or Migita–Stille), we used PMDI as an aromatic C–H bond-bearing unit for direct (hetero)arylation polymerization (DHAP) with 1,4-dibromobenzene as comonomer as a new stabilization strategy. DHAP proved to be an effective tool in the preparation of this polymer, yielding a number-average molecular weight of up to 31 kDa. We studied the effect of side-chain engineering using variable c...

A high molecular weight alternating naphthalene diimide–bithiophene copolymer (poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (PNDIOD-T2)) has been prepared by direct (hetero)arylation polymerization (DHAP). Its structure and properties were investigated in comparison with the Stille-prepared commercial analog, N2200. It was found that the new DHAP-derived PNDIOD-T2 and known N2200 have similar optical absorption spectra and HOMO/LUMO energy levels but slightly different 1H NMR spectra. Inverted all-polymer solar cells using PNDIOD-T2 as the acceptor and PCE12 or PCE10 as the donor polymer showed slightly superior performances compared to similar N2200 devices. All-polymer solar cells with 7.3% efficiency could be achieved with PNDIOD-T2 blends without the use of a processing additive. These results demonstrate that low-cost and eco-friendly DHAP-based n-type semiconducting polymers are promising for developing high performance all-polymer sola...

Highly regioregular poly(3-hexylthiophene) derivatives with varying degrees of fluorine substitution on the thiophene moieties have been demonstrated in photovoltaic devices and characterized using ultraviolet and inverse photoelectron spectroscopy. As fluorine content is increased, an increase in ionization energy of 0.3 eV is observed for 50% fluorination compared to non-fluorinated poly(3-hexylthiophene). The electron affinity is observed to increase to a lesser extent with increased fluorination, consistent with a systematic increase in the optical bandgaps of up to 0.12 eV. Bulk heterojunction photovoltaic devices made from polymer:PC 61 BM blends achieve power conversion efficiencies of 3%, however film morphologies measured using atomic force microscopy indicate that strong phase separation with increasing fluorination limits device performance. UV–vis spectra of thin films of the fluorinated materials exhibit a long tail in the red, extending to longer wavelengths than non-fluorinated poly(3-hexylthiophene). Photovoltaic devices similarly exhibit non-zero quantum efficiency in this region. This behavior has been attributed to a low energy, interchain charge transfer state.

Diketopyrrolopyrrole (DPP) derivatives are among the most efficient materials studied for both polymer solar cells (PSCs) and organic field-effect transistors (OFETs) applications. We report here the synthesis of new fluorinated dithienyldiketopyrrolopyrrole (fDT-DPP) monomers suitable for direct heteroarylation polymerization. fDT-DPP copolymers were then prepared to probe the effect of the fluorination. It was found that they feature deeper HOMO energy levels and smaller bandgaps than their non-fluorinated analogues. Moreover, some fDT-DPP copolymers show ambipolar behavior when tested in OFETs. For example, P2 shows hole mobility up to 0.8 cm2 V–1 s–1 and electron mobility up to 0.5 cm2 V–1 s–1. Inverted PSCs with power conversion efficiency (PCE) up to 7.5% were also obtained for P5. These results reported here (OFETs and PSCs) confirm that the fluorination of dithienyl-DPP moieties improves the performance of organic electronics devices. This study is also evidencing the strength of the direct hetero...

The incorporation of fluorine atoms along the conjugated polymer backbone is an effective strategy to tune the electro-optical properties of donor–acceptor based copolymers. We report here an efficient way to synthesize and purify new mono-fluorinated thiophene derivatives for the synthesis of fluorinated dithienobenzothiadiazole (DTBT) comonomers. It was observed that the reactivity and regioselectivity of the direct (hetero)arylation polymerization (DHAP) were modified upon the amount and the positioning of the fluorine atoms on the DTBT moiety. Indeed, the polymerization time went from 66 h (for non-fluorinated DTBT, M1) to only 11 min (for tetra-fluorinated DTBT, M2). In addition to enhanced reactivity, the degree of fluorination of the flanking thiophene of the DTBT moiety also modulates the electro-optical properties, lowering both the bandgap and stabilizing the ionization energy level. Indeed, P1 (with non-fluorinated flanking thiophene) has a bandgap of 1.73 eV and an ionization energy (IE) of 4....

International audience; The year 2020 marks the 100th anniversary of the first article on poly merization, published by Hermann Staudinger. It is Staudinger who realized that polymers consist of long chains of covalently linked building blocks. Polymers have had a tremendous impact on the society ever since this initial publication. People live in a world that is almost impossible to imagine without synthetic polymers. But what does the future hold for polymer science? In this article, the editors and advisory board of Macromolecular Chemistry and Physics reflect on this question.

International audience; The environmental impact of solution processed organic solar cells (OSCs) can be mitigated by introducing so-called green solvents during the fabrication processes. However, the effects of such green solvents on the molecular-level structures and optoelectronic properties lack in-depth characterization. Here, insights into the structure–processing–property correlation of a PPDT2FBT:PC61BM bulk-heterojunction (BHJ) system processed from a green solvent, ortho-xylene (o-XY), is investigated in comparison with the same blend processed from a traditional halogenated solvent, chlorobenzene (CB). The BHJ blends are characterized with various techniques probing at difference length scales, and an increased donor:acceptor (D:A) interfacial area as well as well-mixed features in the bulk morphologies of the active layer are observed for the o-XY processed BHJ blend. Furthermore, molecular-level differences in the D–A intermolecular interactions at the BHJ interfaces in o-XY and CB cast films are elucidated by 2-dimensional solid-state nuclear magnetic resonance (ssNMR) measurements and analysis. These results are consistent with the device properties, suggesting that the green-solvent-processed devices have longer charge carrier lifetimes and faster charge carrier extraction. The optimized PPDT2FBT:PC61BM devices processed from o-XY can achieve a noteworthy higher power conversion efficiency (PCE) owing to a higher short-circuit current density and fill factor.

Organic polymers have been investigated as active electrode materials in the past few years and although materials with high energy density and tunable redox potential have been developed, their dissolution into the electrolyte and their low electronic conductivity compromised their use in rechargeable batteries. To overcome these drawbacks, seven n-type π-conjugated redox polymers based on 5-alkyl-thieno[3,4-c]pyrrole-4,6-dione have been developed for anode materials of rechargeable batteries. The role of the carbonyl group on the electrochemical activity of these polymers has been demonstrated and the effect of the alkyl chain and the comonomer unit on their electrochemical performance. The redox potential of the polymer has been shown to vary over a range of 400 mV and a polymer with a suitable redox potential of 1.55 V vs. Li/Li+ for an anode of a lithium-ion battery has been found.

Polymer solar cells (PSCs) with a bulk heterojunction (BHJ) structure, i.e. a blend of a p-type conjugated polymer with an n-type semiconductor acceptor, have made rapid progress over the past decade. In comparison with inorganic semiconductor solar cells, PSCs have the advantages of low cost, light weight, solution processability and good mechanical flexibility. In the last few years, various classes of electron-donating polymers have been reported for PSCs. Among them, quinoxaline (Qx) and its derivatives have been widely used as building blocks for optoelectronic applications because they can be easily modified by varying the side chains, such as alkyl chains, conjugated aromatic rings, functional groups, etc. Recently, a power conversion efficiency (PCE) of over 11% was achieved for PSCs with Qx-based polymers. This PCE is among the best for PSCs, and it suggests that Qx-based polymers have great potential for highly efficient PSCs. In this article, we review the recent advances in the design and synthesis of such Qx-based conjugated polymers for photovoltaic applications. Particular attention is paid to the chemical structures of the polymers including flexible chains, conjugated side chains, functional groups, Qx derivatives and the effect of the molecular structure on device performance parameters. We believe that further development of Qx-based polymers will lead to a PCE >12% in the near future.

A series of semi-crystalline, wide band gap (WBG) photovoltaic polymers were synthesized with varying number and topology of fluorine substituents. To decrease intramolecular charge transfer and to modulate the resulting band gap of D–A type copolymers, electron-releasing alkoxy substituents were attached to electron-deficient benzothiadiazole (A) and electron-withdrawing fluorine atoms (0–4F) were substituted onto a 1,4-bis(thiophen-2-yl)benzene unit (D). Intra- and/or interchain noncovalent Coulombic interactions were also incorporated into the polymer backbone to promote planarity and crystalline intermolecular packing. The resulting optical band gap and the valence level were tuned to 1.93–2.15 eV and −5.37 to −5.67 eV, respectively, and strong interchain organization was observed by differential scanning calorimetry, high-resolution transmission electron microscopy and grazing incidence X-ray scattering measurements. The number of fluorine atoms and their position significantly influenced the photophysical, morphological and optoelectronic properties of bulk heterojunctions (BHJs) with these polymers. BHJ photovoltaic devices showed a high power conversion efficiency (PCE) of up to 9.8% with an open-circuit voltage of 0.94–1.03 V. To our knowledge, this PCE is one of the highest values for fullerene-based single BHJ devices with WBG polymers having a band gap of over 1.90 eV. A tandem solar cell was also demonstrated successfully to show a PCE of 10.3% by combining a diketopyrrolopyrrole-based low band gap polymer.

Recent developments on regio-regular and random terpolymers based on a donor/acceptor architecture (D1–A–D2–A or D–A1–D–A2) have shown promising results for their use as donor materials in bulk heterojunction (BHJ) polymer solar cells. New random terpolymers including benzo[1,2-b:4,5-b′]-dithiophene (BDT) as the electron-donor moiety and thiadiazolo[3,4-e]isoindole-5,7-dione (TID) and thieno[3,4-c]pyrrole-4,6-dione (TPD) as electron-accepting moieties were synthesized by Stille cross-coupling polymerization. Incremental addition of TPD (from 0 to 90%) led to the following random terpolymers: P[(BDT-TID)x-(BDT-TPD)y]n. Their electro-optical and photovoltaic properties were investigated. These high molecular weight and highly processable random terpolymers exhibited broad and strong absorption (300–800 nm), moderate bandgaps (1.52 eV to 1.64 eV) and deep-lying HOMO/LUMO energy levels (−5.6 eV and −3.9 eV, respectively). First, the optimized inverted device ITO/ZnO/P1:PC71BM/MoO3/Ag (where P1 is a typical D/A copolymer; TID 100%; TPD 0%) showed a power conversion efficiency up to 6.36% which is higher than the PCE reported in the literature for an analog of P1 (3.42%). Then, devices based on random terpolymers (P2–P10) showed power conversion efficiencies ranging from 5.06% (for P7; 40% TID/60% TPD) up to 6.70% (for P2; 90% TID/10% TPD) when PC61PM is used as the electron acceptor. A PCE as high as 7.30%, a Voc of 0.81 V, a Jsc of 13.86 mA cm−2 and a FF of 65% were achieved for P2 when PC71PM was used. This PCE is among the highest PCE values reported for random terpolymer-based polymer solar cells.

New phosphine-based ligands and DFT calculations for defect-free conjugated polymers by direct (hetero)arylation polymerization (DHAP)., Direct (hetero)arylation polymerization (DHAP) has emerged as a valuable and atom-economical alternative to traditional cross-coupling methods for the synthesis of low-cost and efficient conjugated polymers for organic electronics. However, when applied to the synthesis of certain (hetero)arene-based materials, a lack of C–H bond selectivity has been observed. To prevent such undesirable side-reactions, we report the design and synthesis of new, bulky, phosphine-based ligands that significantly enhance selectivity of the DHAP process for both halogenated and non-halogenated electron-rich and electron-deficient thiophene-based comonomers. To better understand the selectivity issues, density functional theory (DFT) calculations have been performed on various halogenated and non-halogenated electron-rich and electron-deficient thiophene-based comonomers. Calculations showed that the presence of bromine atoms decreases the energy of activation (E a) of the adjacent C–H bonds, allowing undesirable β-defects for some brominated aromatic units. Both calculations and the new ligands should lead to the rational design of monomers and methods for the preparation of defect-free conjugated polymers from DHAP.

We systematically varied the degree of fluorination along the backbone of a series of highly regioregular 3-hexylthiophene-based polymers, P3HT-50F, P3HT-33F, and P3HT-25F, in which 50%, 33%, and 25% of the thiophene units within the polymer chain contain fluorine atoms in the available 4-position, respectively. These materials were homopolymerized using the Kumada catalyst transfer polycondensation method from a set of mono-fluorinated bi-, ter-, and quarterthiophenes to ensure high polymer regioregularity and evenly spaced fluorine atoms along the conjugated thiophene backbone. The monomers were obtained from a synthetic route consisting of iterative Migita–Stille couplings of fluorinated and non-fluorinated 3-hexylthiophenes. The effect of the fluorine atoms on both polymer structure and properties is presented, with supporting quantum mechanical calculations that rationalize the intrinsic conformation preferences of the three P3HT derivatives. P3HT-50F (Mn = 34 kg/mol, 98.5% rr), P3HT-33F (Mn = 46 k...

Conjugated polymers have attracted much attention in recent years, as they can combine the best features of metals or inorganic semiconducting materials (excellent electrical and optical properties) with those of synthetic polymers (mechanical flexibility, simple processing, and low-cost production), thereby creating altogether new scientific synergies and technological opportunities. In the search for more efficient synthetic methods for the preparation of conjugated polymers, this Perspective reports advances in the field of direct (hetero)arylation polymerization. This recently developed polymerization method encompasses the formation of carbon-carbon bonds between simple (hetero)arenes and (hetero)aryl halides, reducing both the number of synthetic steps and the production of organometallic byproducts. Along these lines, we describe the most general and adaptable reaction conditions for the preparation of high-molecular-weight, defect-free conjugated polymers. We also discuss the bottleneck presented by the utilization of certain brominated thiophene units and propose some potential solutions. It is, however, firmly believed that this polymerization method will become a versatile tool in the field of conjugated polymers by providing a desirable atom-economical alternative to standard cross-coupling polymerization reactions.

This study reports the synthesis and characterization of poly(3-hexylthiophene) (P3HT) from a direct heteroarylation polymerization of two isomeric monomers, 2-bromo-3-hexylthiophene (monomer 1) and 2-bromo-4-hexylthiophene (monomer 2). Using the Herrmann–Beller catalyst along with P(o-NMe2Ph)3, the resulting polymers are obtained in excellent yields and exhibit a good number-average molecular weight (Mn of 33 and 16 kDa, respectively). Detailed 1H NMR analyses reveal less than 1% of homocouplings and no evidence of β-branching. Dehalogenation is identified as the main chain termination step and preferentially occurs on monomer 2. The melting temperature (237 °C) and hole mobility (up to 0.19 cm2 V−1.s−1) of the nearly defect-free P3HT obtained from this simple polymerization of monomer 1 are comparable, if not superior, to those obtained with commercially available GRIM and Rieke samples.

Narrow bandgap n-type organic semiconductors (n-OS) have attracted great attention in recent years as acceptors in organic solar cells (OSCs), due to their easily tuned absorption and electronic energy levels in comparison with fullerene acceptors. Herein, a new n-OS acceptor, Y5, with an electron-deficient-core-based fused structure is designed and synthesized, which exhibits a strong absorption in the 600-900 nm region with an extinction coefficient of 1.24 × 105 cm-1 , and an electron mobility of 2.11 × 10-4 cm2 V-1 s-1 . By blending Y5 with three types of common medium-bandgap polymers (J61, PBDB-T, and TTFQx-T1) as donors, all devices exhibit high short-circuit current densities over 20 mA cm-2 . As a result, the power conversion efficiency of the Y5-based OSCs with J61, TTFQx-T1, and PBDB-T reaches 11.0%, 13.1%, and 14.1%, respectively. This indicates that Y5 is a universal and highly efficient n-OS acceptor for applications in organic solar cells.

High efficiency, excellent stability, and air processability are all important factors to consider in endeavoring to push forward the real-world application of organic solar cells. Herein, an air-processed inverted photovoltaic device built upon a low-bandgap, air-stable, phenanthridinone-based ter-polymer (C150 H218 N6 O6 S4 )n (PDPPPTD) and [6,6]-phenyl-C61 -butyric acid methyl ester (PC61 BM) without involving any additive engineering processes yields a high efficiency of 6.34%. The PDPPPTD/PC61 BM devices also exhibit superior thermal stability and photo-stability as well as long-term stability in ambient atmosphere without any device encapsulation, which show less performance decay as compared to most of the reported organic solar cells. In view of their great potential, solvent additive engineering via adding p-anisaldehyde (AA) is attempted, leading to a further improved efficiency of 7.41%, one of the highest efficiencies for all air-processed and stable organic photovoltaic devices. Moreover, the device stability under different ambient conditions is also further improved with the AA additive engineering. Various characterizations are conducted to probe the structural, morphology, and chemical information in order to correlate the structure with photovoltaic performance. This work paves a way for developing a new generation of air-processable organic solar cells for possible commercial application.

Direct (hetero)arylation polymerization exploits the palladium-catalyzed activation of aromatic CH bonds for the atom-economical synthesis of conjugated polymers for a wide range of applications. This account outlines how direct arylation methodologies overcome many of the limitations of contemporary polymerization techniques at both the research and production scale, and explains how monomer design and reaction conditions must be tailored to ensure high polymer molecular weight, yield, and structural integrity. Current research aims to improve further this reaction's profile as a sustainable methodology while at the same time making it competitive with the Migita-Stille and Miyaura-Suzuki polymerizations both in scope of accessible structures and synthetic efficiency. This feature article charts the recent developments and future directions of CH activation research as it moves toward becoming at once an industrially feasible, environmentally friendly, and synthetically powerful polymerization technique.