A Dual‐Function Elastomer Enables Highly Efficient and Stretchable Layer‐by‐Layer Organic Solar Cells

ABSTRACT The mechanical stability of organic solar cells (OSCs) remains insufficient for emerging applications such as flexible electronics, and conventional approaches for enhancing flexibility are still limited. This study proposes an innovative strategy that incorporates thermoplastic polyurethane (TPU) into the small‐molecule active layer via a layer‐by‐layer processing technique. On one hand, the nano‐confinement effect between TPU and L8‐BO enhances their interaction, leading to optimized molecular packing. This leads to outstanding power conversion efficiencies (PCEs) of 20.04% and 14.53% for rigid and stretchable devices with 1% TPU. Further, the D18/L8‐BO:BTP‐eC9 device achieves a notably higher efficiency of 20.37%. On the other hand, TPU effectively mitigates the brittleness of the small‐molecule material, thereby significantly improving the mechanical properties of the film. The crack‐onset strain of the active layer increased from 5.3% for the pristine film to 7.6% with 1% TPU, and further to 12.1% with 5% TPU. This work opens a new avenue for advancing the application of OSCs in wearable electronics.