High-Performance Intrinsically Stretchable Polymer Solar Cell with Record Efficiency and Stretchability Enabled by Thymine-Functionalized Terpolymer

Chlorinated Bithiophene Imide-Based n-Type Polymers: Synthesis, Structure-Property Correlations, and Applications in Organic Electronic Devices

Developing electron-deficient (hetero)arenes with optimized geometries and electronic properties is imperative for advancing n-type polymers and organic electronic devices. We report here the design and synthesis of two chlorinated imide-functionalized electron-deficient heteroarenes, namely chlorine-substituted bithiophene imide (ClBTI) and its fused dimer (ClBTI2). The corresponding polymers show a near-planar framework, appropriate frontier molecular orbital levels, and good solubility. When integrated into organic thin-film transistors, ClBTI2-based n-type polymer afforded unipolar electron mobility of up to 0.48 cm2 V-1 s-1. The binary all-PSCs based on PM6 and new polymers show a power conversion efficiency (PCE) exceeding 1%. Interestingly, by introducing these polymers with ordered structure, high crystallinity, and sizable electron mobility as the third component into the host system PM6:PY-IT, continuous interpenetrating networks with large fibrillar structures can be formed. Investigations of charge transfer kinetics and energy loss analyses unveiled that ClBTI2-based n-type polymer P(ClBTI2-BTI) enables optimized charge transport, reduced charge recombination, and minimized non-radiative loss within the all-polymer ternary blends, yielding a remarkable PCE of 19.35% (certified: 19.20%) through optimizing the state-of-the-art PM6:PY-IT blend. The structure-property-performance relationships provide valuable insights into the design of electron-deficient (hetero)arenes and n-type polymers, marking a great progress in the development of high-performance n-type polymers for organic electronic devices.

Fluorine-, Nitrogen-, and Boron-Functionalized Polymer Electrolytes for Advanced Lithium Metal Batteries

Polymer electrolytes (PEs) have emerged as alternatives to conventional liquid electrolytes in lithium metal batteries (LMBs) by addressing critical safety and performance challenges, including flame hazards, dendrite growth, and interfacial instability. While oxygen-based PEs, such as poly(ethylene oxide), have been widely investigated, their limited ionic conductivity and susceptibility to electrochemical degradation under high-voltage operation have prompted the exploration of heteroatom-functionalized PEs. Incorporating heteroatoms significantly enhances ion transport, electrochemical stability, and mechanical properties─all critical factors for robust and reliable LMB performance. This review focuses on fluorine-, nitrogen-, and boron-functionalized PEs, highlighting their distinctive features and design strategies for LMB applications. Recent developments and key design principles are summarized in the context of high-performance PEs for safer and more reliable LMBs for advanced energy storage applications.

Bioinspired Deformable Antireflective Materials by Block Copolymer Self-Assembly

Antireflective surface is a crucial component for high-performance photonic systems but has been principally focused on hard, flat device geometry. We present an antireflective strategy for deformable device geometry that combines superior optical performance with mechanical robustness. Bioinspired nanohole arrays are embedded into a transparent polymer layer by exploiting block copolymer self-assembly. The resultant nanoengineered surface reduces light reflection by over 70% across the visible spectrum compared to a nonpatterned surface, owing to gradual refractive index along nanohole geometry that mediates optical impedance mismatch with the air interface, as supported by simulation studies. Adoption of interconnected nanostructures facilitates efficient dissipation of external mechanical stress, ensuring high mechanical resilience, even under repeated nonlinear deformation cycles. Furthermore, multifunctionality with self-cleaning capabilities is demonstrated, attributed to genuine hydrophobicity of nanostructured geometry. Our straightforward strategy delivers a promising solution for next-generation optical and optoelectronic systems commonly involved in complex and deformable design configurations.

High-Performance Intrinsically-Stretchable Organic Solar Cells Enabled by Electron Acceptors with Flexible Linkers

Intrinsically stretchable organic solar cells (IS-OSCs) are emerging as promising candidates for powering next-generation wearable electronics. However, developing molecular design strategies to achieve both high efficiency and mechanical robustness in IS-OSCs remains a significant challenge. In this work, we present a novel approach by synthesizing a dimerized electron acceptor (DY-FBrL) that enables rigid OSCs with a high power conversion efficiency (PCE) of 18.75 % and a crack-onset strain (COS) of 18.54 %. The enhanced PCE and stretchability of DY-FBrL-based devices are attributed to its extended π-conjugated backbone and elongated side chains. Furthermore, we introduce an innovative polymerized acceptor (PDY-FL), synthesized via the polymerization of DY-FBrL. While PDY-FL-based devices exhibit a slightly lower PCE of 14.13 %, they achieve a significantly higher COS of 23.45 %, representing one of the highest PCEs reported for polymerized acceptors containing only flexible linkers. Consequently, IS-OSCs fabricated using DY-FBrL and PDY-FL achieve notable PCEs of 14.31 % and 11.61 %, respectively. Additionally, the device stretchability improves progressively from Y6 (strain at PCE80%=11 %), to DY-FBrL (strain at PCE80%=23 %), and PDY-FL (strain at PCE80%=31 %). This study presents a promising molecular design strategy for tailoring electron acceptor structures, offering a new pathway to develop high-performance IS-OSCs with enhanced mechanical properties.

Tuning Charge Transport Behavior of Isoindigo-Based Polymers from Balanced Ambipolar to n-Type Preferred via Hydrogen Bond Formation

Hydrogen bond, as a type of high-strength non-covalent interaction, is adopted in the construction of highly planar polymer frameworks. In this context, a new type of conjugated polymer, P(5MeOII-Pyr) is synthesized by copolymerizing 5,5'-dimethoxy isoindigo (5MeOII) with pyrazine (Pyr). By demethylation, P(5OHII-Pyr) is obtained, in which the hydrogen bond between the hydroxyl group on the isoindigo core and the nitrogen atom on the pyrazine core is formed. Compared to P(5MeOII-Pyr), P(5OHII-Pyr) exhibits a red shift of ∼20 nm in UV-vis absorption, which is related to the planarization of the polymeric backbone due to the hydrogen bond formation. Both materials demonstrate high thermal stability, with thermal decomposition temperatures around 400 °C. Organic field-effect transistor devices (OFETs) with a top-gate bottom-contact configuration are fabricated using these two materials and their charge transport behaviors are compared. Notably, the electron mobility of P(5OHII-Pyr) increases more than tenfold compared to P(5MeOII-Pyr), while its hole mobility is greatly suppressed, making it a n-type-transport preferred material. This improvement is primarily due to the introduction of hydroxyl groups, which makes the polymer more planar, allowing better delocalization of LUMO, thereby facilitating electron transport along the polymer backbone.

Fine-Tuning Intra/Inter-Molecular Interaction via Ternary Copolymerization Strategy to Obtain Efficient Polymer Donors

Incorporating a third component through ternary copolymerization strategy has proven to be a promising and effective approach for further improving the device performance of polymer donors. However, terpolymer donors typically exhibit negative effects on molecular stacking and weaken charge transport due to the irregular distribution of the polymer skeleton. Herein, two terpolymers PBBQ-5 (5% ff-Qx) and PBBQ-10 (10% ff-Qx) are developed by introducing the difluoro-2-(3-hexyldecyloxy) quinoxaline (ff-Qx) to the main chain of PM6. The introduction of ff-Qx unit not only enables the terpolymers to possess N···S noncovalent intramolecular interactions that contribute to enlarge molecular planarity and enhance intramolecular interaction but also can fine-tuning electrostatic potential (ESP) values of the related polymers, thereby regulate intermolecular interactions with acceptor by electrostatic force. After blending with L8-BO, the PBBQ-5:L8-BO-based blend film exhibits appreciated miscibility, desirable phase separation sizes, and more ordered molecular packing than the analogs. Consequently, an impressive power conversion efficiency (PCE) as high as 19.54% is realized in PBBQ-5-based devices, which set a new record for Qx-based polymer solar cells. The work emphasizes the drawbacks of terpolymers and provides a new pathway for developing high-performance polymer donors by optimizing intra/inter-molecular interaction.

Halogen-Free Wide Band Gap Polymer Donors Based on Dicyanobithiophene for Efficient Organic Solar Cells

Conjugated polymer donors have always been one of the important components of organic solar cells (OSCs), particularly those featuring simple synthetic routes, proper energy levels, and appropriate aggregation behavior. In this work, we employed a nonfused electron-deficient building block, dicyanobithiophene (2CT), for constructing high-performance donors. Combining this with side-chain engineering, two novel halogen-free polymer donors, PB2CT-BO and PB2CT-HD, were reported. PB2CT-BO with shorter alkyl chains on the thiophene π bridges exhibited enhanced packing ordering and improved polymer crystallinity. When paired with BTP-CN-HD as the electron acceptor, the PB2CT-BO-based OSC attained an impressive power conversion efficiency (PCE) of 14.2% within a bulk-heterojunction (BHJ) configuration. Additionally, the active layers were refined through a layer-by-layer (LbL) approach, leading to a more organized molecular packing and an improved fibrillar network. Consequently, the OSC employing PB2CT-BO processed with the LbL approach achieved a notable PCE of 15.3%. This enhancement is credited to a reduced energy loss (Eloss) of 0.514 eV and the formation of a favorable morphology. This study highlights the considerable promise of the 2CT unit in the progression of high-efficiency polymer donors with a reduced Eloss.

Mechanically robust and stretchable organic solar cells plasticized by small-molecule acceptors

Emerging wearable devices would benefit from integrating ductile photovoltaic light-harvesting power sources. In this work, we report a small-molecule acceptor (SMA), also known as a non-fullerene acceptor (NFA), designed for stretchable organic solar cell (s-OSC) blends with large mechanical compliance and performance. Blends of the organosilane-functionalized SMA BTP-Si4 with the polymer donor PNTB6-Cl achieved a power conversion efficiency (PCE) of >16% and ultimate strain (εu) of >95%. Typical SMAs suppress OSC blend ductility, but the addition of BTP-Si4 enhances it. Although BTP-Si4 is less crystalline than other SMAs, it retains considerable electron mobility and is highly miscible with PNTB6-Cl and is essential for enhancing εu. Thus, s-OSCs with PCE > 14% and operating normally under various deformations (>80% PCE retention under an 80% strain) were demonstrated. Analysis of several SMA-polymer blends revealed general molecular structure-miscibility-stretchability relationships for designing ductile blends.

Dynamic hydrogen-bonding enables high-performance and mechanically robust organic solar cells processed with non-halogenated solvent

Developing active-layer systems with both high performance and mechanical robustness is a crucial step towards achieving future commercialization of flexible and stretchable organic solar cells (OSCs). Herein, we design and synthesize a series of acceptors BTA-C6, BTA-E3, BTA-E6, and BTA-E9, featuring the side chains of hexyl, and 3, 6, and 9 carbon-chain with ethyl ester end groups respectively. Benefiting from suitable phase separation and vertical phase distribution, the PM6:BTA-E3-based OSCs processed by o-xylene exhibit lower energy loss and improved charge transport characteristic and achieve a power conversion efficiency of 19.92% (certified 19.57%), which stands as the highest recorded value in binary OSCs processed by green solvents. Moreover, due to the additional hydrogen-bonding provided by ethyl ester side chain, the PM6:BTA-E3-based active-layer systems achieve enhanced stretchability and thermal stability. Our work reveals the significance of dynamic hydrogen-bonding in improving the photovoltaic performance, mechanical robustness, and morphological stability of OSCs.

An n-Doping Cross-Linkable Quinoidal Compound as an Electron Transport Material for Fully Stretchable Inverted Organic Solar Cells

The photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, an intrinsically stretchable ETL for inverted OSCs through a side-chain cross-linking strategy has been developed. Specifically, cross-linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr-PEI-50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack-onset strain>45 %). When used as the ETL in inverted OSCs, QBr-PEI-50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27 % and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr-PEI-50 in fully stretchable inverted OSCs yielded a PCE of 14.01 %, and 80 % of the initial PCE was maintained after 21 % strain, showcasing its potential for wearable electronics.

Molecular Design of Active Layer for High-Performance Stretchable Organic Solar Cells

Stretchable organic solar cells (SOSCs) have advanced rapidly in the last few years as power sources required to realize portable and wearable electronics become available. Through rational material and device engineering, SOSCs are now able to retain their photovoltaic performance even when subjected to repeated mechanical deformations. However, reconciling a high efficiency and an excellent stretchability is still a huge challenge, and the development of SOSCs has lagged far behind that of flexible OSCs. In this perspective article, recent strategies for imparting mechanical robustness to SOSCs while maintaining high power conversion efficiency are reviewed, with emphasis on the molecular design of active layers. Initially, an overview of molecular design approaches and recent research advances is provided in improving the stretchability of active layers, including donors, acceptors, and single-component materials. Subsequently, another common strategy for regulating photovoltaic and mechanical properties of SOSCs, namely multi-component system, is summarized and analyzed. Lastly, considering that SOSCs research is in its infancy, the current challenges and future directions are pointed out.

Spatial Conformation Engineering of Aromatic Ketones for Highly Efficient and Stable Perovskite Solar Cells

Carbonyl-containing materials employed in state-of-the-art hybrid lead halide perovskite solar cells (PSCs) exhibit a strong structure-dependent electron donor effect that predominates in defect passivation. However, the impact of the molecular spatial conformation on the efficacy of carbonyl-containing passivators remains ambiguous, hindering the advancement of molecular design for passivating materials. Herein, we show that altering the spatial torsion angle of aromatic ketones from twisted to planar configurations, as seen in benzophenone (BP, 27.2°), anthrone (AR, 15.3°), and 9-fluorenone (FO, 0°), leads to a notable increment of the electron cloud density around the carbonyl group, thus improving the passivation ability for lead-based defects. Consequently, the PSC performance also relies on the torsion angle of the aromatic ketones, with the coplanar FO-based PSC achieving a highest power conversion efficiency (PCE) of 25.13% and retaining 92% of its initial efficiency after 1000 h of operation at the maximum power point under continuous 1-sun illumination (ISOS-L-1I). Moreover, a perovskite mini-module (14.0 cm2) containing FO exhibits a PCE of 20.19%. Our findings highlight the influence of molecular conformation on the passivation effect of the carbonyl group, offering deeper insight into the design and development of aromatic ketones as passivators for highly efficient and stable PSCs.

Molecular-Scale Geometric Design: Zigzag-Structured Intrinsically Stretchable Polymer Semiconductors

Orienting intelligence and multifunction, stretchable semiconductors are of great significance in constructing next-generation human-friendly wearable electronic devices. Nevertheless, rendering semiconducting polymers mechanical stretchability without compromising intrinsic electrical performance remains a major challenge. Combining geometry-innovated inorganic systems and structure-tailored organic semiconductors, a molecular-scale geometric design strategy is proposed to obtain high-performance intrinsically stretchable polymer semiconductors. Originating from the linear regioregular conjugated polymer and corresponding para-modified near-linear counterpart, a series of zigzag-structured semiconducting polymers are developed with diverse ortho-type and meta-type kinking units quantitatively incorporated. They showcase huge edges in realizing stretchability enhancement for conformational transition, likewise with long-range π-aggregation and short-range torsion disorder taking effect. Assisted by additional heteroatom embedment and flexible alkyl-chain attachment, mechanical stretchability and carrier mobility could afford a two-way promotion. Among zigzag-structured species, o-OC8-5% with the initial field-effect mobility up to 1.92 cm2 V-1 s-1 still delivers 1.43 and 1.37 cm2 V-1 s-1 under 100% strain with charge transport parallel and perpendicular to the stretching direction, respectively, accompanied by outstanding performance retention and cyclic stability. This molecular design strategy contributes to an in-depth exploration of prospective intrinsically stretchable semiconductors for cutting-edge electronic devices.

Advances in Stretchable Organic Photovoltaics: Flexible Transparent Electrodes and Deformable Active Layer Design

Stretchable organic photovoltaics (OPVs) have attracted significant attention as promising power sources for wearable electronic systems owing to their superior robustness under repetitive tensile strains and their good compatibility. However, reconciling a high power-conversion efficiency and a reasonable flexibility is a tremendous challenge. In addition, the development of stretchable OPVs must be accelerated to satisfy the increasing requirements of niche markets for mechanical robustness. Stretchable OPV devices can be classified as either structurally or intrinsically stretchable. This work reviews recent advances in stretchable OPVs, including the design of mechanically robust transparent electrodes, photovoltaic materials, and devices. Initially, an overview of the characteristics and recent research progress in the areas of structurally and intrinsically stretchable OPVs is provided. Subsequently, research into flexible and stretchable transparent electrodes that directly affect the performances of stretchable OPVs is summarized and analyzed. Overall, this review aims to provide an in-depth understanding of the intrinsic properties of highly efficient and deformable active materials, while also emphasizing advanced strategies for simultaneously improving the photovoltaic performance and mechanical flexibility of the active layer, including material design, multi-component settings, and structural optimization.

A Three-in-One Hybrid Strategy for High-Performance Semiconducting Polymers Processed from Anisole

The development of semiconducting polymers with good processability in green solvents and competitive electrical performance is essential for realizing sustainable large-scale manufacturing and commercialization of organic electronics. A major obstacle is the processability-performance dichotomy that is dictated by the lack of ideal building blocks with balanced polarity, solubility, electronic structures, and molecular conformation. Herein, through the integration of donor, quinoid and acceptor units, an unprecedented building block, namely TQBT, is introduced for constructing a serial of conjugated polymers. The TQBT, distinct in non-symmetric structure and high dipole moment, imparts enhanced solubility in anisole-a green solvent-to the polymer TQBT-T. Furthermore, PTQBT-T possess a highly rigid and planar backbone owing to the nearly coplanar geometry and quinoidal nature of TQBT, resulting in strong aggregation in solution and localized aggregates in film. Remarkably, PTQBT-T films spuncast from anisole exhibit a hole mobility of 2.30 cm2 V-1 s-1, which is record high for green solvent-processable semiconducting polymers via spin-coating, together with commendable operational and storage stability. The hybrid building block emerges as a pioneering electroactive unit, shedding light on future design strategies in high-performance semiconducting polymers compatible with green processing and marking a significant stride towards ecofriendly organic electronics.

Intrinsically stretchable organic photovoltaics by redistributing strain to PEDOT:PSS with enhanced stretchability and interfacial adhesion

Intrinsically stretchable organic photovoltaics have emerged as a prominent candidate for the next-generation wearable power generators regarding their structural design flexibility, omnidirectional stretchability, and in-plane deformability. However, formulating strategies to fabricate intrinsically stretchable organic photovoltaics that exhibit mechanical robustness under both repetitive strain cycles and high tensile strains remains challenging. Herein, we demonstrate high-performance intrinsically stretchable organic photovoltaics with an initial power conversion efficiency of 14.2%, exceptional stretchability (80% of the initial power conversion efficiency maintained at 52% tensile strain), and cyclic mechanical durability (95% of the initial power conversion efficiency retained after 100 strain cycles at 10%). The stretchability is primarily realised by delocalising and redistributing the strain in the active layer to a highly stretchable PEDOT:PSS electrode developed with a straightforward incorporation of ION E, which simultaneously enhances the stretchability of PEDOT:PSS itself and meanwhile reinforces the interfacial adhesion with the polyurethane substrate. Both enhancements are pivotal factors ensuring the excellent mechanical durability of the PEDOT:PSS electrode, which further effectively delays the crack initiation and propagation in the top active layer, and enables the limited performance degradation under high tensile strains and repetitive strain cycles.

Dimerized Acceptors with Conjugate-Break Linker Enable Highly Efficient and Mechanically Robust Organic Solar Cells

Designing new acceptors is critical for intrinsically stretchable organic solar cells (IS-OSCs) with high efficiency and mechanical robustness. However, nearly all stretchable polymer acceptors exhibit limited efficiency and high-performance small molecular acceptors are very brittle. In this regard, we select thienylene-alkane-thienylene (TAT) as the conjugate-break linker and synthesize four dimerized acceptors by the regulation of connecting sites and halogen substitutions. It is found that the connecting sites and halogen substitutions considerably impact the overall electronic structures, aggregation behaviors, and charge transport properties. Benefiting from the optimization of the molecular structure, the dimerized acceptor exhibits rational phase separation within the blend films, which significantly facilitates exciton dissociation while effectively suppressing charge recombination processes. Consequently, FDY-m-TAT-based rigid OSCs render the highest power conversion efficiency (PCE) of 18.07 % among reported acceptors containing conjugate-break linker. Most importantly, FDY-m-TAT-based IS-OSCs achieve high PCE (14.29 %) and remarkable stretchability (crack-onset strain [COS]=18.23 %), significantly surpassing Y6-based counterpart (PCE=12.80 % and COS=8.50 %). To sum up, these findings demonstrate that dimerized acceptors containing conjugate-break linkers have immense potential in developing highly efficient and mechanically robust OSCs.

Stability of organic solar cells: toward commercial applications

Organic solar cells (OSCs) have attracted a great deal of attention in the field of clean solar energy due to their advantages of transparency, flexibility, low cost and light weight. Introducing them to the market enables seamless integration into buildings and windows, while also supporting wearable, portable electronics and internet-of-things (IoT) devices. With the development of photovoltaic materials and the optimization of fabrication technology, the power conversion efficiencies (PCEs) of OSCs have rapidly improved and now exceed 20%. However, there is a significant lack of focus on material stability and device lifetime, causing a severe hindrance to commercial applications. In this review, we carefully review important strategies employed to improve the stability of OSCs over the past three years from the perspectives of material design and device engineering. Furthermore, we analyze and discuss the current important progress in terms of air, light, thermal and mechanical stability. Finally, we propose the future research directions to overcome the challenges in achieving highly stable OSCs. We expect that this review will contribute to solving the stability problem of OSCs, eventually paving the way for commercial applications in the near future.

Achieving Record-High Stretchability and Mechanical Stability in Organic Photovoltaic Blends with a Dilute-absorber Strategy

Organic solar cells (OSCs) have potential for applications in wearable electronics. Except for high power conversion efficiency (PCE), excellent tensile properties and mechanical stability are required for achieving high-performance wearable OSCs, while the present metrics barely meet the stretchable requirements. Herein, this work proposes a facile and low-cost strategy for constructing intrinsically stretchable OSCs by introducing a readily accessible polymer elastomer as a diluent for all-polymer photovoltaic blends. Remarkably, record-high stretchability with a fracture strain of up to 1000% and mechanical stability with elastic recovery >90% under cyclic tensile tests are realized in the OSCs active layers for the first time. Specifically, the tensile properties of best-performing all-polymer photovoltaic blends are increased by up to 250 times after blending. Previously unattainable performance metrics (fracture strain >50% and PCE >10%) are achieved simultaneously for the resulting photovoltaic films. Furthermore, an overall evaluation parameter y is proposed for the efficiency-cost- stretchability balance of photovoltaic blend films. The y value of dilute-absorber system is two orders of magnitude greater than those of prior state-of-the-art systems. Additionally, intrinsically stretchable devices are prepared to showcase the mechanical stability. Overall, this work offers a new avenue for constructing and comprehensively evaluating intrinsically stretchable organic electronic films.

Control of Properties through Hydrogen Bonding Interactions in Conjugated Polymers

Molecular design is crucial for endowing conjugated polymers (CPs) with unique properties and enhanced electronic performance. Introducing Hydrogen-bonding (H-bonding) into CPs has been a broadly exploited, yet still emerging strategy capable of tuning a range of properties encompassing solubility, crystallinity, electronic properties, solid-state morphology, and stability, as well as mechanical properties and self-healing properties. Different H-bonding groups can be utilized to tailor CPs properties based on the applications of interest. This review provides an overview of classes of H-bonding CPs (assorted by the different H-bond functional groups), the synthetic methods to introduce the corresponding H-bond functional groups and the impact of H-bonding in CPs on corresponding electronic and materials properties. Recent advances in addressing the trade-off between electronic performance and mechanical durability are also highlighted. Furthermore, insights into future directions and prospects for H-bonded CPs are discussed.

Intrinsically Stretchable and Healable Polymer Semiconductors

In recent decades, polymer semiconductors, extensively employed as charge transport layers in devices like organic field-effect transistors (OFETs), have undergone thorough investigation due to their capacity for large-area solution processing, making them promising for mass production. Research efforts have been twofold: enhancing the charge mobilities of polymer semiconductors and augmenting their mechanical properties to meet the demands of flexible devices. Significant progress has been made in both realms, propelling the practical application of polymer semiconductors in flexible electronics. However, integrating excellent semiconducting and mechanical properties into a single polymer still remains a significant challenge. This review intends to introduce the design strategies and discuss the properties of high-charge mobility stretchable conjugated polymers. In addition, another key challenge faced in this cutting-edge field is maintaining stable semiconducting performance during long-term mechanical deformations. Therefore, this review also discusses the development of healable polymer semiconductors as a promising avenue to improve the lifetime of stretchable device. In conclusion, challenges and outline future research perspectives in this interdisciplinary field are highlighted.

Regulating Phase Separation Kinetics for High-Efficiency and Mechanically Robust All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) possess excellent operation stability and mechanical robustness than other types of organic solar cells, thereby attracting considerable attention for wearable flexible electron devices. However, the power conversion efficiencies (PCEs) of all-PSCs are still lagging behind those of small-molecule-acceptor-based systems owing to the limitation of photoactive materials and unsatisfactory blend morphology. In this work, a novel terpolymer, denoted as PBDB-TFCl (poly4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b″]dithiophene-1,3-bis(2-ethylhexyl)-5,7-di(thiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c″]dithiophene-4,8-dione-4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene), is used as an electron donor coupled with a ternary strategy to optimize the performance of all-PSCs. The addition of PBDB-TCl unit deepens the highest occupied molecular orbital energy level, reducing voltage losses. Moreover, the introduction of the guest donor (D18-Cl) effectively regulates the phase-transition kinetics of PBDB-TFCl:D18-Cl:PY-IT during the film formation, leading to ideal size of aggregations and enhanced crystallinity. PBDB-TFCl:D18-Cl:PY-IT devices exhibit a PCE of 18.6% (certified as 18.3%), judged as the highest value so far obtained with all-PSCs. Besides, based on the ternary active layer, the manufactured 36 cm2 flexible modules exhibit a PCE of 15.1%. Meanwhile, the ternary PSCs exhibit superior photostability and mechanical stability. In summary, the proposed strategy, based on molecular design and the ternary strategy, allows optimization of the all-polymer blend morphology and improvement of the photovoltaic performance for stable large-scale flexible PSCs.

Thorough Optimization for Intrinsically Stretchable Organic Photovoltaics

The development of intrinsically stretchable organic photovoltaics (is-OPVs) with a high efficiency is of significance for practical application. However, their efficiencies lag far behind those of rigid or even flexible counterparts. To address this issue, an advanced top-illuminated OPV is designed and fabricated, which is intrinsically stretchable and has a high performance, through systematic optimizations from material to device. First, the stretchability of the active layer is largely increased by adding a low-elastic-modulus elastomer of styrene-ethylene-propylene-styrene tri-block copolymer (SEPS). Second, the stretchability and conductivity of the opaque electrode are enhanced by a conductive polymer/metal (denoted as M-PH1000@Ag) composite electrode strategy. Third, the optical and electrical properties of a sliver nanowire transparent electrode are improved by a solvent vapor annealing strategy. High-performance is-OPVs are successfully fabricated with a top-illuminated structure, which provides a record-high efficiency of 16.23%. Additionally, by incorporating 5-10% elastomer, a balance between the efficiency and stretchability of the is-OPVs is achieved. This study provides valuable insights into material and device optimizations for high-efficiency is-OPVs, with a low-cost production and excellent stretchability, which indicates a high potential for future applications of OPVs.