Stress‐Dissipative Network Design Unlocks Stretchy All‐Polymer Photovoltaics with Record Mechanical Robustness

Abstract Intrinsically stretchy all‐polymer solar cells (IS‐APSCs) offer potential for wearable and conformable energy‐harvesting devices but remain considerable distant from commercial adoption. Recently, thermoplastic elastomers have emerged as effective additives to enhance the intrinsic stretchability and mechanical resilience of organic photovoltaics. However, the underlying mechanisms by which elastomers influence the physical characteristics of stretchy photovoltaics remain underexplored. Here, this dilemma is uncovered through leveraging advanced Infrared Nanospectroscopy analysis and X‐ray scattering characterizations, revealing crucial insights that significantly retain the photovoltaic performance of IS‐APSCs. Medium molecular weight elastomeric additives are identified to form stress‐dissipative networks at relatively low concentrations, providing the most effective mechanical reinforcement and enabling the highest efficiency in IS‐APSCs. They possess high performance retention after hundreds of stretching cycles, significantly outperforming lower/higher molecular weight analogs. For the first time, finite element analysis are shown to accurately capture the tensile behavior of these blend films, in excellent agreement with experimental observations. Furthermore, the elastic modulus of the blend films, comprising elastomeric additives of varying molecular weights and conjugated polymers, closely follows theoretical predictions from the Coran‐Patel model. By bridging polymer physics, mechanical modeling, and device engineering, this work will aid in designing high‐efficiency stretchy photovoltaic devices.