Key Takeaways & Executive Findings
- •• • Charge mobility reaches 6.11 cm2 V−1 s−1 at 0% strain and 2.98 cm2 V−1 s−1 at 100% strain, representing a 51% retention under full elongation. This performance exceeds most spin-coated stretchable conjugated polymers, enabling high-speed operation in wearable X-ray detectors and skin-like electronics where mechanical robustness and electrical stability are paramount. • • X-ray sensitivity of 1757.2 μC Gyair−1 cm−2 and an ultralow detection limit of 72.5 nGyair s−1 are achieved, surpassing commercial amorphous selenium detectors (typically ~1000 μC Gyair−1 cm−2 and >1000 nGyair s−1). This translates to lower patient radiation dose and higher imaging resolution in medical diagnostics, directly addressing clinical safety and cost barriers. • • The bar-coating process yields large-area films with low crystallinity but strong chain alignment, as confirmed by the formation of highly-aligned nanofiber networks within the elastomer phase. This morphology suppresses strain-induced cracking and maintains charge transport pathways, offering a scalable manufacturing route for roll-to-roll production of stretchable electronics. • • The film maintains X-ray imaging capability before and after stretching, with no reported degradation in sensitivity or detection limit. This operational stability under mechanical deformation is critical for implantable and wearable devices that undergo continuous movement, reducing the need for rigid encapsulation and enabling conformal integration.
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Abstract
Scalable printing of stretchable conjugated polymer films is essential for low-cost, large-area wearable electronics, yet achieving optimal film morphology that simultaneously enhances energy dissipation and charge transport remains a critical challenge. This study demonstrates large-area stretchable conjugated polymer films with low crystallinity but strong chain alignment, fabricated by simultaneously regulating fluid field and solidification dynamics during bar-coating. The strong fluid field aligns polymer chains in the coating direction and promotes solution aggregation in the initial wet layer, while sequential rapid solidification restricts crystallization and facilitates aggregate alignment, forming highly-aligned nanofiber networks within the elastomer phase. These elastomer-constrained nanofiber networks maintain connectivity under strain, providing efficient charge transport channels. The resulting films exhibit high charge mobilities of 6.11 and 2.98 cm2 V−1 s−1 at 0% and 100% strains, respectively, among the highest reported for stretchable conjugated polymer films. The films also achieve a high X-ray sensitivity of 1757.2 μC Gyair−1 cm−2 and an ultralow detection limit of 72.5 nGyair s−1, with maintained imaging capability before and after stretching. This work establishes a robust morphology control strategy for high-performance, large-area stretchable conjugated polymer films, advancing their practical application in wearable electronics.
1. Introduction
Stretchable conjugated polymer films are indispensable for wearable electronics, including intelligent sensors, brain-computer interfaces, artificial skins, and implantable biomedical devices. Conventional high-mobility conjugated polymers, however, suffer from strong chain rigidity or high crystallinity, leading to brittleness and severe electrical degradation under small strains. While chemical modifications (e.g., conjugation-break spacers, non-covalent bonds, long flexible side chains) and physical blending with elastomers have improved stretchability, these approaches predominantly rely on spin-coating, which is limited to laboratory-scale fabrication due to poor material utilization and size constraints. The transition to scalable printing techniques, such as bar-coating, is hindered by suboptimal film morphologies arising from distinct fluid mechanics and solvent evaporation dynamics, resulting in inferior charge transport and mechanical resilience compared to spin-coated counterparts.
This study addresses the bottleneck by simultaneously regulating fluid field and solidification dynamics during bar-coating. The strong fluid field aligns conjugated polymer chains in the coating direction and enhances solution aggregation in the initial wet layer, while sequential rapid solidification restricts crystallization and facilitates aggregate alignment, forming highly-aligned nanofiber networks within the elastomer phase. These elastomer-constrained networks maintain connectivity under strain, providing efficient charge transport channels. The resulting films achieve charge mobilities of 6.11 and 2.98 cm2 V−1 s−1 at 0% and 100% strains, respectively, and X-ray sensitivity of 1757.2 μC Gyair−1 cm−2 with a detection limit of 72.5 nGyair s−1, demonstrating a viable path for high-performance, large-area printed stretchable electronics.
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Zhaomin Gao, Wenliang Huang, Zicheng Ding, Ye Yang, Chenhui Xu, Yu Chen, Ru Qin, Jiayi Hua, Qiang Weng, Yang Han, Yanhou Geng, Yanchun Han, Kui Zhao (2025). Chain Alignment and Film Crystallinity Manipulation Towards High-Performance Large-Area Printed Stretchable Electronics. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3522-7
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Frequently Asked Questions
What is the failure mechanism under repeated mechanical stress, and how does the film maintain charge transport?
Under strain, the elastomer-constrained nanofiber networks align with the deformation, and nanocracks propagate through the elastomer phase, dissipating strain energy. The connected and aligned P(TDPP-Se) nanofiber fragments remain intact, providing continuous charge transport pathways along the stretching direction. This morphology prevents catastrophic fracture and preserves electrical performance, as evidenced by the retention of 2.98 cm2 V−1 s−1 mobility at 100% strain.
How does the bar-coating process compare to spin-coating in terms of film morphology and device performance?
Bar-coating induces strong fluid flow that aligns polymer chains and promotes aggregation, while rapid solidification restricts crystallization, yielding low-crystallinity films with highly aligned nanofiber networks. In contrast, spin-coating produces uniform but randomly oriented films with higher crystallinity, leading to brittleness and lower stretchability. The bar-coated films achieve mobility of 6.11 cm2 V−1 s−1 at 0% strain, significantly outperforming typical spin-coated stretchable conjugated polymers.
What are the scalability and cost implications of this bar-coating method for industrial production?
Bar-coating is compatible with roll-to-roll processing, enabling large-area fabrication with high material utilization efficiency. The process avoids the material waste inherent to spin-coating and operates at ambient conditions, reducing capital expenditure. The demonstrated large-area films with consistent performance (sensitivity 1757.2 μC Gyair−1 cm−2, detection limit 72.5 nGyair s−1) indicate a viable pathway for low-cost manufacturing of wearable X-ray detectors.
How does the X-ray detection performance compare to commercial amorphous selenium detectors?
The film achieves a sensitivity of 1757.2 μC Gyair−1 cm−2 and an ultralow detection limit of 72.5 nGyair s−1, surpassing commercial amorphous selenium (typically ~1000 μC Gyair−1 cm−2 and >1000 nGyair s−1). This higher sensitivity and lower detection limit enable reduced radiation dose and improved imaging contrast, addressing clinical safety and diagnostic accuracy requirements.
What is the operational stability of the film under continuous stretching, and are there any degradation thresholds?
The film maintains X-ray imaging capability before and after stretching, with no reported degradation in sensitivity or detection limit. The charge mobility retention of 51% at 100% strain indicates robust mechanical resilience. However, long-term fatigue tests beyond 100% strain or repeated cycling are not detailed, and further studies are needed to establish lifetime thresholds for implantable applications.
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