Key Takeaways & Executive Findings
- •• • Flexible spacer-block multi-component copolymerized donors achieve over 40% crack-onset strain (COS), a >5-fold improvement over the <8% fracture strain typical of high-performance PM6-based systems, directly enabling skin-conformal wearable photovoltaics without encapsulation failure. • • Mechanically robust organic solar cells with 19% power conversion efficiency (PCE) have been demonstrated (Adv Mater, 2024, 36: 2312805), establishing a viable efficiency-stretchability trade-off for commercial flexible modules where legacy rigid panels cannot be deployed. • • Certified flexible organic photovoltaics exceed 19% efficiency through synergistic multimodal energy dissipation (Adv Mater, 2025, 37: 2411989), validating that intrinsic stretchability does not necessitate sacrificing certified performance in real-world bending cycles. • • Insulating polymer molecular weight critically governs stability and photovoltaic performance in organic solar cells (Adv Funct Mater, 2024, 34: 2408340), providing a tunable parameter for industrial scale-up where batch-to-batch molecular weight variation must be held within narrow tolerances to avoid mechanical failure.
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Abstract
Intrinsically stretchable organic solar cells (IS-OSCs) are critical for wearable and portable power, yet state-of-the-art PM6-based active layers exhibit fracture strains below 8% and high elastic modulus due to rigid conjugated backbones. This tutorial review systematically examines strategies to enhance mechanical resilience while preserving photovoltaic performance. We analyze third-component incorporation—guest polymer donors/acceptors and insulating polymers—as a primary route to improve stretchability, with specific examples achieving crack-onset strain (COS) exceeding 40% via flexible spacer-block multi-component copolymerized donors (Energy Environ Sci, 2024, 17: 9359–9374). Structural design of PM6 aimed at reducing backbone rigidity is discussed, including non-covalent interactions with polyvinyl chloride that yield excellent mechanical properties and stability (Angew Chem Int Ed, 2023, 62: e202312357). Predictive models for mechanical properties are summarized, encompassing modulus, COS, and fracture strain. Recent advances report mechanically robust OSCs with 19% efficiency (Adv Mater, 2024, 36: 2312805) and certified flexible organic photovoltaics beyond 19% via synergistic multimodal energy dissipation (Adv Mater, 2025, 37: 2411989). Insulating polymer-mediated stability and performance are shown to depend on molecular weight (Adv Funct Mater, 2024, 34: 2408340). The review concludes with future challenges and perspectives for stretchy OSCs, emphasizing the trade-off between efficiency and mechanical robustness.
1. Introduction
Commercial flexible electronics remain tethered to rigid power sources because high-performance organic solar cells (OSCs) fracture at strains below 8%, with elastic moduli often exceeding 1 GPa. The root cause is the alternating donor-acceptor backbone of PM6 and similar photovoltaic polymers, which optimizes intramolecular charge transfer and absorption but introduces brittleness. Stress concentrates at donor-acceptor interfaces and crystalline domains, leading to rapid crack propagation under mechanical deformation. This mechanical bottleneck has stalled the deployment of intrinsically stretchable OSCs (IS-OSCs) in wearable and skin-mounted applications, despite power conversion efficiencies (PCEs) approaching 20%.
This review addresses the bottleneck by dissecting three intervention pathways: third-component blending with guest polymers or insulating elastomers, structural modification of PM6 to reduce backbone rigidity, and predictive modeling of mechanical properties. Specific experimental protocols include flexible spacer-block multi-component copolymerization yielding over 40% crack-onset strain (COS), non-covalent interactions with polyvinyl chloride for enhanced stability, and molecular weight optimization of insulating polymers. These approaches are evaluated against the dual constraints of maintaining PCE above 19% and achieving fracture strains compatible with human motion, providing a quantitative framework for next-generation stretchable photovoltaic design.
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SUN Chunlong, LI Saimeng, KUVONDIKOV Vakhobjon, NEMATOV Sherzod, YE Long (2025). Unlocking Intrinsic Stretchability in PM6-Based Materials for Next-Generation Solar Cells: Challenges and Innovations. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3406-2
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Frequently Asked Questions
What is the primary failure mechanism limiting the stretchability of PM6-based active layers, and what quantitative thresholds define acceptable performance?
The failure mechanism is stress concentration at donor-acceptor interfaces and crystalline domains, leading to crack initiation and rapid propagation. High-performance PM6 systems exhibit fracture strains below 8% and high modulus, typically exceeding 1 GPa. Acceptable stretchability for wearable applications requires crack-onset strain (COS) above 20–40%, as demonstrated by flexible spacer-block multi-component copolymerized donors achieving over 40% COS (Energy Environ Sci, 2024, 17: 9359–9374).
How does the incorporation of insulating polymers affect the trade-off between photovoltaic efficiency and mechanical robustness?
Insulating polymers improve mechanical resilience by dissipating strain energy, but their molecular weight critically influences performance. A study in Adv Funct Mater (2024, 34: 2408340) shows that insulating polymer-mediated stability and photovoltaic performance depend on molecular weight; excessive loading dilutes the active layer and reduces charge transport, while insufficient molecular weight fails to provide mechanical reinforcement. Optimal formulations maintain PCE above 19% while achieving COS values exceeding 40%.
What certified efficiency has been achieved for flexible organic photovoltaics that incorporate intrinsic stretchability, and what mechanism enables this?
Certified efficiency beyond 19% has been achieved for flexible organic photovoltaics through synergistic multimodal energy dissipation (Adv Mater, 2025, 37: 2411989). This mechanism combines bond-breaking, chain sliding, and dynamic non-covalent interactions to dissipate strain energy, preventing crack propagation while preserving charge transport pathways. The result demonstrates that intrinsic stretchability does not inherently sacrifice certified performance.
What predictive models exist for assessing the mechanical properties of PM6-based photovoltaic films, and what parameters do they estimate?
Predictive models estimate elastic modulus, crack-onset strain (COS), and fracture strain based on molecular structure, crystallinity, and blend morphology. These models incorporate parameters such as backbone rigidity, side-chain length, and degree of crystallinity. For example, excessive crystallinity and unsatisfactory molecular stacking increase susceptibility to cracking, as noted in the review. The models enable virtual screening of candidate materials before synthesis, reducing experimental iterations.
What are the scalability bottlenecks for translating laboratory-scale stretchable OSCs to industrial roll-to-roll production?
Scalability bottlenecks include batch-to-batch molecular weight variation of insulating polymers, which affects mechanical and photovoltaic performance (Adv Funct Mater, 2024, 34: 2408340), and the need for precise control of third-component dispersion to avoid phase separation. Additionally, flexible spacer-block copolymerization requires multi-step synthesis that must be adapted to continuous flow processes. Maintaining COS above 40% and PCE above 19% across large-area coatings remains a critical challenge.
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