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Stretchable electronics have received intense attention due to their broad application prospects in many areas, and can withstand large deformations and form close contact with curved surfaces. Stretchable conductors are vital components of stretchable electronic devices used in wearables, soft robots, and human-machine interactions. Recent advances in stretchable conductors have motivated basic scientific and technological research efforts. Here, we outline and analyse the development of stretchable conductors in transistors and circuits, and examine advances in materials, device engineering, and preparation technologies. We divide the existing approaches to constructing stretchable transistors with stretchable conductors into the following two types: geometric engineering and intrinsic stretchability engineering. Finally, we consider the challenges and outlook in this field for delivering stretchable electronics.

To achieve high-performance polymer semiconductors, it is crucially important to explore novel and effective synthesis strategies. Here, chain-extending polymerization as a synthesis strategy to design polymer semiconductors is introduced. Furthermore, we demonstrate its superiority over a conventional synthesis strategy─one-pot polymerization. Diketopyrrolopyrrole-thieno[3,2

The widespread use of electrically conductive metal-organic frameworks (EC-MOFs) in high-performance devices is limited by the lack of facile methods for synthesizing large-area thin films on the desired substrates. Herein, we propose a spin-coating interfacial self-assembly approach to in situ synthesize high-quality centimeter-sized copper benzenehexathiol (Cu-BHT) MOFs on diverse substrates in only 5 s. The film thickness (ranging from 5 to 35 nm) and surface morphology can be precisely tuned by controlling the reaction time. The gas sensor based on the 10 nm thick Cu-BHT film exhibits a low limit of detection (0.23 ppm) and high selectivity value (>30) in sensing NH3 at ultralow driving voltages (0.01 V). Moreover, the Cu-BHT films retain their initial sensor performance after 1000 repetitive bending cycles at a bending radius of 3 mm. Density functional theory calculations suggest that Cu2c sites induced by crystal particles on the film surface can improve the sensing performance. This facile and ultrafast approach for in situ synthesis of large-area EC-MOF films on diverse substrates with tunable thickness on a nanometer scale should facilitate application of EC-MOFs in flexible electronic device arrays.

Multi-stimuli-responsive Janus composite nanoparticles (JNPs) of poly(

Conjugated polymers based on poly(3,4-propylenedioxythiophene) (PProDOT) backbones are widely studied for electrochromics, due to their favourable redox properties including enhanced optical contrast and fast switching kinetics in nonaqueous electrolytes. The usual hydrophobic nature of these polymers renders them redox-inactive when interfaced with aqueous salt solutions. This work illustrates an effective side chain modification approach where polar amide functional groups are incorporated into the polymer side chains to attain redox switching in aqueous electrolytes while maintaining a high contrast. The impact of substitutional modifications (in terms of primary and secondary amide groups) on the interaction with hydrated and non-hydrated ions is studied using electrochemical and spectroscopic techniques to elucidate the underlying mechanisms leading to redox activity in aqueous electrolytes. The presence of amide groups is beneficial in terms of reducing the oxidation onset potential, making them attractive candidates for electrochromics in both nonaqueous and aqueous electrolytes.

Understanding high-temperature operation in organic semiconductors remains elusive. Here, we studied the effect of two alkyl side-chains, 2-octyldodecyl (C1) and 4-decyltetracecyl (C3), on the ther...

Cu-benzenehexathiol (Cu-BHT) has attracted significant attention due to its record high electrical conductivity and crystal defects Cu

The widespread use of electrically conductive metal-organic frameworks (EC-MOFs) in high-performance devices is limited by the lack of facile methods for synthesizing large-area thin films on the desired substrates. Herein, we propose a spin-coating interfacial self-assembly approach to

We successfully design and construct urchin-like non-precious-metal bifunctional oxygen electrocatalysts via a two-step pyrolysis process, where nitrogen, sulfur co-doped carbon nanotube frameworks are grafted onto mesoporous cobalt sulfide/nitrogen, sulfur co-doped carbon spheres. The urchin-like structure grants large electrochemically active area, good electron and mass transfer capability, as well as excellent structural stability. Nitrogen, sulfur co-doped carbon can synergistically enhance the catalytic activity of cobalt sulfide sites, and also contribute to the exposure of heteroatom-induced active sites, such as, pyridinic N, graphitic N, and C-S-C. Hence, benefiting from the unique architecture and efficient catalytic sites, the resulting catalysts demonstrate excellent bifunctional catalytic activities with a positive half-wave potential of 0.860 V vs. RHE for oxygen reduction reaction and low overpotential of ∼390 mV at the current density of 10 mA cm−2 for oxygen evolution reaction in alkaline medium, which can rank them among one of the most promising cobalt-based bifunctional oxygen electrocatalysts reported previously.

The exploration of novel electron-deficient building blocks is a key task for developing high-performance polymer semiconductors in organic thin-film transistors. In view of the situation of the lack of strong electron-deficient building blocks, we designed two novel π-extended isoindigo-based electron-deficient building blocks, IVI and F4IVI. Owing to the strong electron-deficient nature and the extended π-conjugated system of the two acceptor units, their copolymers, PIVI2T and PF4IVI2T, containing 2,2′-bithiophene donor units, are endowed with deep-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and strong intermolecular interactions. In comparison to PIVI2T, the fluorinated PF4IVI2T exhibits stronger intra- and intermolecular interactions, lower HOMO/LUMO energy levels up to −5.74/–4.17 eV, and more ordered molecular packing with a smaller π–π stacking distance of up to 3.53 A, resulting in an excellent ambipolar transporting behavior and a prom...

The development of efficient, low-cost, and durable electrocatalysts toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for overall water splitting associated with renewable energy conversion and storage. Carbon-based nanomaterials have been widely employed as electrocatalysts for the independent HER or OER; however, research on bifunctional metal-free electrocatalysts for water splitting is still in its infancy and remains a formidable challenge to develop highly active catalysts for future applications. Here we report a highly active defect-rich, carbon-based, bifunctional metal-free water splitting electrocatalyst, prepared by a template approach, in which a nitrogen-enriched polydopamine analogue is used as the carbon precursor. The resultant defect-rich porous carbon (DRPC) exhibits a large specific surface area with a hierarchically micro/mesoporous structure and a high nitrogen doping content with rich pyridinic N. Accordingly, the newly developed DRPC electrocatalysts display superb bifunctional catalytic activities for both the HER and the OER in alkaline solution, outperforming all other reported metal-free catalysts. Significantly, the DRPC catalyst couple-based alkaline water electrolyzer with strong durability delivers a 10 mA cm−2 overall water splitting current at a considerably low voltage of 1.74 V, and a demonstration of a self-powered electrochemical water splitting system is also presented, highlighting its great potential for practical applications.

A bioinspired polydopamine derivative was prepared by self-polymerization of 6-(2-aminoethyl)-3-hydroxypyridin-2(1H)-one (AHPO) in an alkaline aqueous medium. It was used as a precursor to produce nanocapsules of pyridinic N-rich carbon with a desired N doping content by using silica nanoparticles as the template. These N-doped nanocapsules exhibited superior electrocatalytic activity and stability towards the oxygen reduction reaction (ORR), lending an attractive alternative to the Pt catalyst. This work provides an important insight into the rational designing of bioinspired polymers for the development of functional carbon materials with excellent properties.

Balanced carrier transport is observed in acceptor-acceptor (A-A′) type polymer for ambipolar organic thin-film transistors (OTFTs). It is found that the incorporation of two electron-accepting moieties (BTz and IIG) into a polymer main chain to form A-A′ polymer PIIG-BTz could lower highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and facilitate good molecular stacking of the polymer. Ambipolar transistor behaviour for PIIG-BTz, with the balanced hole and electron mobilities of 0.030 and 0.022 cm2 V−1 s−1 was observed in OTFT devices, respectively. The study in this work reveals that the utilization of acceptor-acceptor (A-A′) structure in polymer main chain can be a feasible strategy to develop ambipolar polymer semiconductors.

We developed a synthetic strategy for enhancing organic thin-film transistor performances of polymer semiconductors through the modification of the side chain to optimize the stacking conformation and the conjugated backbone to decrease the π–π stacking distance of polymers. Our studies demonstrate that the role of bulky alkyl chains attached to the donor unit or the acceptor unit is especially crucial for molecular stacking and aggregation and thus the OTFT device performance of polymers. However, with a larger π–π stacking distance in the thin film, the polymer with a bulky alkyl chain attached at the acceptor (P2) shows almost two orders of magnitude higher mobility than that with a bulky alkyl chain attached at the donor (P1). The better performance for P2 is attributed to the bulky alkyl chain at the acceptor which allows more coplanarity of the P2 backbone in the solution state, which leads to self-assembly, and finally forms a highly ordered layer-by-layer lamellar packing for P2 during spin-coating. Further improved performances were obtained by introducing two thiophene units into the polymer backbone to give P3, due to closer π–π stacking and in-plane π-stacking alignment in the thin film and a higher HOMO energy level. Therefore, an optimized device performance was realized through subtle modification of the polymer structure, including both the main chain and the side chain, which provides an insight into structure–property relationships for high-mobility polymer semiconductors.

A new copolymer (P(DPP4T-co-BDT)) was synthesized by Stille coupling polymerization of 3,6-bis(5′-bromo-[2,2′-bithiophen]-5-yl)-2,5-bis(2-octyldodecyl)pyrrolo-[3,4-c]-pyrrole-1,4(2H,5H)-dione and 2,6-bis(trimethyltin)-4,8-dimethoxybenzo[1,2-b:3,4-b′]dithiophene. P(DPP4T-co-BDT) showed good solution processability, good thermal stability with decomposition temperature of >330 °C, and strong and broad absorption in the range of 500–900 nm. Field-effect transistors based on P(DPP4T-co-BDT) thin films exhibited a hole mobility of up to 0.047 cm2 V−1 s−1, an on/off current ratio of 106, and a threshold voltage of −5 V after thermal annealing at 200 °C. Thin film phototransistors based on P(DPP4T-co-BDT) exhibited a photoresponsivity of up to 4.0 × 103 A W−1 and a photocurrent/dark-current ratio of 6.8 × 105 under white light irradiation with a low light intensity (9.7 μW cm−2).

Two new diketopyrrolopyrrole-based π-conjugated copolymers (PDPP6T and PDPP7T) have been synthesized by Stille coupling polymerization of 3,6-bis(5′-bromo-[2,2′-bithiophen]-5-yl)-2,5-bis(2-octyldodecyl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione with α,α′-bis(trimethylstannyl)-bithiophene and α,α′-bis(trimethylstannyl)-terthiophene, respectively. The impressive high mobility of 3.94 cm2 V–1 s–1 for the polymer with sextetthiophene (6T) and of 2.82 cm2 V–1s–1 for polymer with septetthiophene (7T) is acquired. It is found that the introduction of longer β-unsubstituted oliogothiophene unit in DPP-based copolymers has a great influence on the molecular weight and solubility of the DPP-oligothiophene copolymers that finally affects the organic thin-film transistor (OTFT) performances, indicating that a suitable number of thiophene group in β-unsubstituted oligothiophene exists for such a kind of copolymer to exhibit the best OTFT performances. This work also reveals the significance in the design of D–A copolymer...

A novel donor-acceptor-donor-acceptor (D-A1-D-A2) π-conjugated copolymer (PDBPyDT2FBT) has been prepared by Stille coupling reaction. It is found that PDBPyDT2FBT exhibits low LUMO energy level mainly because of multiple electron-deficient units and donor-acceptor interaction, which is favorable to obtain more efficient electron injection and transport in organic thin-film transistors (OTFTs). Moreover, introducing two electron-deficient moieties into the thiophene-containing copolymer increases the length of conjugated main chain and enhances the coplanarity of the backbone, which may be beneficial for promoting the molecular crystallinity and improving molecular ordering capability at low temperatures. High electron and hole mobilities up to 0.65 and 0.24 cm(2) V(-1) s(-1) were obtained at relatively low annealing temperatures of 100 and 80 °C, respectively, implying that PDBPyDT2FBT is a promising ambipolar polymer semiconductor applied in low-cost and large-area manufacturing of OTFTs.

A new diketopyrrolopyrrole-based π-conjugated copolymer (PDPP5T) with high molecular weight has been synthesized by Stille coupling polymerization of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione with α,α′-bis(trimethylstannyl)-terthiophene. Its hole mobility without thermal annealing reaches 1.08 cm2 V–1 s–1, and a higher hole mobility of 3.46 cm2 V–1 s–1 is obtained annealed at 200 °C directly in an air atmosphere. This indicates that introducing a longer β-unsubstituted quinquethiophene (5T) unit into the main-chain of DPP-oligothiophene copolymer produces much pronounced p-type behavior and also reduces the steric hindrance of the bulk side-chain groups, which is favorable to enhance the molecular ordering capability at low temperatures and improve the organic thin-film transistors (OTFT) performances. This work demonstrates that PDPP5T is a promising material that can be applied to the cost-effective and large-scale production of OTFTs.

The exploration of novel molecular architectures is crucial for the design of high-performance ambipolar polymer semiconductors. Here, a "triple-acceptors architecture" strategy to design the ambipolar polymer DPP-2T-DPP-TBT is introduced. The utilization of this architecture enables DPP-2T-DPP-TBT to achieve deep-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of -5.38/-4.19 eV, and strong intermolecular interactions, which are favorable for hole/electron injection and intermolecular hopping through π-stacking. All these factors result in excellent ambipolar transport characteristics and promising applications in complementary-like circuits for DPP-2T-DPP-TBT under ambient conditions with high hole/electron mobilities and a gain value of up to 3.01/3.84 cm2 V-1 s-1 and 171, respectively, which are among the best performances in ambipolar polymer organic thin-film transistors and associated complementary-like circuits, especially in top-gate device configuration with low-cost glass as substrates. These results demonstrate that the "triple-acceptors architecture" strategy is an effective way for designing high-performance ambipolar polymer semiconductors.

Since the report of the first diketopyrrolopyrrole (DPP)-based polymer semi-conductor, such polymers have received considerable attention as a promising candidate for high-performance polymer semiconductors in organic thin-film transistors (OTFTs). This Progress Report summarizes the advances in the molecular design of high-mobility DPP-based polymers reported in the last few years, especially focusing on the molecular design of these polymers in respect of tuning the backbone and side chains, and discussing the influences of structural modification of the backbone and side chains on the properties and device performance of corresponding DPP-based polymers. This provides insights for the development of new and high-mobility polymer semiconductors.