Improved Stretchability of Sequential‐Deposited Elastomer‐Based Ternary Active Layers via Photo Crosslinking

ABSTRACT Stretchable organic solar cells (OSCs) hold significant promise as light‐harvesting power sources in wearable electronics. Physical blending highly‐deformable elastomer into rigid photovoltaic components represents a simple and effective approach to enhance film stretchability. However, the mechanical and photovoltaic performance of elastomer‐based active layers are generally inferior to those achieved through chemical approaches. Herein, we report a high‐performance stretchable active layer that combines photo crosslinking with sequential deposition of an elastomer‐based ternary system poly[2,6‐(4,8‐bis(5‐(2‐ethylhexyl‐3‐fluoro)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b']dithiophene))‐alt‐5,5'‐(5,8‐bis(4‐(2‐butyloctyl)thiophen‐2‐yl)dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2‐c][1,2,5]thiadiazole)] (D18)/2,2'‐((2Z,2'Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2‐g]thieno[2',3':4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene)bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalonitrile) (Y6): polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS), achieving a power conversion efficiency of 15.38% and a crack‐onset strain of 35.91%. Crosslinking D18 with an azide compound ethane‐1,2‐diyl bis(4‐azido‐2,3,5,6‐tetrafluorobenzoate) (2BX) in the bottom layer not only produces a 3D covalent network, but also results in a low‐crystallinity film with a reduced glass transition temperature. These structure changes contribute to delayed large‐scale chain slippage and enhanced strain energy dissipation, leading to approximately 100% and 40% improvements in the stretchability of D18 film and full active layer. Moreover, the charge generation and transport behaviors are just slightly affected with moderate microstructure change, enabling the device to retain 94% of initial efficiency. Ultimately, the optimal active layer achieves an efficiency‐stretchability factor of 5.52%, ranking among the highest reported values for stretchable active layer systems.