From Solution to Stretched Film: Probing and Controlling Microstructure in Conjugated Polymer Systems for Emerging Stretchable Organic Photovoltaics

The advancement of stretchable organic photovoltaics is hindered by a fundamental trade-off between high optoelectronic performance and mechanical durability, in particular, a challenge rooted in the complex microstructure of conjugated polymers and their blends. This review addresses a critical literature gap on the microstructure of various conjugated polymer systems by systematically examining how multiscale microstructural evolution, from solution-state aggregation to solid-state morphology and dynamic response under strain, can be characterized, understood, and rationally controlled. Analysis begins with how advanced X-ray and neutron scattering techniques elucidate the formative solution-aggregation structures that dictate the final solid-state morphology. Subsequently, multiscale characterization methods for thin films are reviewed, alongside material design strategies, such as elastomeric modifiers, engineered to optimize phase-separated morphologies for simultaneous conductivity and mechanical flexibility. A key focus is the transition beyond static X-ray scattering analysis to explore the dynamic evolution of microstructure under mechanical stretching, thereby underscoring the pivotal role of in situ and operando characterization in revealing deformation and failure mechanisms. By integrating insights across these scales, this review aims to distill rational design principles, offer a coherent processing-structure-performance framework, and provide a complete picture for the predictive design of next-generation intrinsically robust stretchable photovoltaics and related electronics.