Sequentially Deposited Elastomer‐Based Ternary Active Layer for High‐Performance Stretchable Organic Solar Cells

Abstract Stretchable organic solar cells (OSCs) with high power conversion efficiency and good mechanical deformation are promising as power sources for wearable electronics. However, synergistic improvement of both photovoltaic efficiency and mechanical ductility is challenging for state‐of‐the‐art polymer donor: non‐fullerene acceptor (NFA)‐based photovoltaic active layers. Here, a high‐performance stretchable OSC with a power conversion efficiency of 16.54% and a crack‐onset strain of 26.38% by synergetic optimization film microstructure of sequentially deposited ternary active layer consisting of a polymer donor 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), an NFA 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), and an elastomer polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) is reported. Adding a low‐content solvent additive para‐xylene into main solvent carbon disulfide induces high‐density fibers networks with low crystallinity in bottom D18 layer, and this further suppresses the large phase separation between Y6 and SEBS in top layer. Moreover, incorporating a solid additive 1,3‐dibromo‐5‐chlorobenzene with better compatibility with Y6 can promote Y6 dispersions to form smaller ordered domains in SEBS matrix. Finally, the optimal ternary active layer shows significantly higher efficiency and stretchability, resulting in a large efficiency‐stretchability factor of 4.36%, which is among the best values for stretchable OSCs.