Multiscale X-Ray Measurements Reveal How Stretchable Polymer Semiconductors Dissipate Stress

by Brooke Kuei

SCIENTIFIC ACHIEVEMENT

With the help of the Advanced Light Source (ALS), researchers revealed a two-stage structural evolution that enables stretchable conjugated polymers to dissipate stress while maintaining charge transport.

SIGNIFICANCE AND IMPACT

This work establishes a design framework for next-generation intrinsically stretchable organic photovoltaics and other deformable electronic devices.

Large diagram showing all techniques used in separate squares. Top left corner shows graph of NEXAFS technique, next to it are shapes that show orientation and torsion. The right side of shows circular color patterns. Bottom left shows spread out red shape for beam. — Researchers used a suite of in situ X-ray techniques across multiple length scales to reveal a gradual, two-stage structural adaptation in stretchable conjugated polymers that enables stress dissipation while preserving charge transport pathways. Top left: NEXAFS revealed initial polymer chain alignment followed by intrachain conformational changes during stretching. Top right: TReXS tracked crystallite deformation and orientation in situ, revealing rapid crystallite fragmentation, while GIWAXS on stretched films captured changes in π–π stacking and crystallite orientation. Bottom right: RSoXS characterized mesoscale morphology, showing strain-induced fibril reorganization and progressive alignment along the stretch direction.

The tradeoff between performance and stretchability

Conjugated polymers combine tunable optoelectronic properties with mechanical flexibility, making them attractive materials for deformable electronics like stretchable organic photovoltaics (OPVs) and wearable sensors. Efficient charge transport in these materials depends on strong π–π stacking, but this face-to-face alignment of conjugated backbones also makes materials more rigid, creating a fundamental trade-off between stretchability and electronic performance.

Intrinsically stretchable conjugated polymers have demonstrated the ability to maintain electronic functionality under strain, but how multiscale structural changes evolve in real time during stretching has not been directly observed. In a study published recently in Nature Communications, an international research team used X-ray techniques at the ALS and National Synchrotron Light Source II (NSLS-II) to track how stretchable conjugated polymers reorganize during deformation, revealing mechanisms that enable both mechanical resilience and efficient charge transport.

Multimodal, in situ X-ray techniques for understanding stretching

The researchers studied a model stretchable conjugated polymer, P(NDI2OD-TD), and employed a multimodal approach across complementary scattering and spectroscopy techniques to observe molecular rearrangements, nanoscale crystalline domain behavior, and larger mesoscale morphology evolution during deformation. To monitor structural changes under strain in real time, they used a custom in situ stage designed by the ALS.

At the molecular scale, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the ALS Beamline 11.0.1.2, combined with simulations by the Molecular Foundry uncovered changes in polymer backbone orientation and intrachain torsion—how the polymer chains align and twist—during stretching. At larger length scales, tender resonant X-ray scattering (TReXS) at NSLS-II tracked crystallite deformation, fragmentation, and orientation during stretching, while grazing-incidence wide-angle X-ray scattering (GIWAXS) of stretched films at ALS Beamline 7.3.3 revealed changes in π–π stacking and crystallite orientation. Resonant soft X-ray scattering (RSoXS) at ALS Beamline 11.0.1.2 further probed mesoscale morphology, tracking the alignment and reorganization of fibrillar domains during stretching.

Three charts with lines of data points and labels of the three techniquest NEXAFS, TReXS, and RSoXS. — In situ NEXAFS, TReXS, and RSoXS provided complementary information on multiscale structural evolution in conjugated polymer films during stretching. Top left: NEXAFS results combined with simulations showed changes in chain alignment and dihedral angle between molecular units (intrachain torsion) with strain. Top right: TReXS tracked crystallite evolution, revealing loss of order in parallel and perpendicular crystallites. Bottom: RSoXS captures mesoscale morphological reorganization, in which isotropic domains evolve into an oriented, X-shaped scattering pattern reflecting progressive fibrillar alignment with increasing strain.

Two-stage structural evolution during stretching

This multimodal approach revealed a previously unreported two-stage evolution, an initial phase of chain alignment and crystallite fragmentation followed by intrachain torsion, with structural changes occurring across molecular to mesoscale length scales throughout deformation. Coupled with device measurements showing that electronic performance is partially maintained under strain, these sequential adaptations explain how deformation is distributed across multiple length scales, enabling the material to dissipate stress while sustaining charge transport pathways.

These insights, which would not have been possible with ex situ or single-technique approaches, establish design principles for intrinsically stretchable polymer semiconductors that combine mechanical resilience with high optoelectronic performance for next-generation stretchable organic photovoltaics and other flexible electronics.

Contacts: Cheng Wang

Researchers: W. Zhong (South China University of Technology and Shanghai Jiao Tong University); G. Freychet (NSLS-II and Univ. Grenoble Alpes); G. M. Su (ALS and Berkeley Lab); S. Wang, X. Luo, X. Liu, W. Yang, L. Yu, Y. Li, L. Ying, and F. Huang (South China University of Technology); X. Wu (Berkeley Lab); T. J. Ferron and C. Wang (ALS); T. P. Russell (Berkeley Lab and University of Massachusetts Amherst); Y. Zhang and F. Liu (Shanghai Jiao Tong University).

Funding: The National Key R&D Program of China, National Natural Science Foundation of China, China Postdoctoral Science Foundation, and State Key Lab of Luminescent Materials and Devices, South China University of Technology. Operation of the Lawrencium computational cluster is supported by Berkeley Lab. Operation of the ALS, Molecular Foundry, and NSLS-II are supported by the US Department of Energy, Office of Science, Basic Energy Sciences program.

Publication: W. Zhong, G. Freychet, G.M. Su, S. Wang, X. Luo, X. Liu, W. Yang, L. Yu, X. Wu, Y. Li, T.J. Ferron, T.P. Russell, L. Ying, F. Huang, Y. Zhang, C. Wang, and F. Liu, “Correlative molecular-to-mesoscale evolution in conjugated polymers for intrinsically stretchable organic photovoltaics,” Nat. Commun. 17, 2980 (2026), doi:10.1038/s41467-025-68265-4.