Quantitative Fracture Analysis of All‐Polymer Active Layers for Intrinsically Stretchable Organic Solar Cells

Comprehensive Summary

Stretchy organic solar cells require active layers that can not only tolerate large tensile deformation but also resist crack propagation after damage initiation. However, conventional mechanical descriptors such as crack‐onset strain and fracture strain provide limited information on how cracks evolve and dissipate energy in deformable photovoltaic films. Here, we provide a quantitative fracture‐analysis framework for elastomer‐toughened all‐polymer photovoltaic active layers by combining optical crack tracking, crack‐aspect‐ratio analysis, film‐on‐water fracture testing, crack‐tip atomic force microscopy, and finite‐element analysis. Using PM6:PYF‐T‐o:SEBS films as a model system, we show that increasing SEBS content transforms fracture from rapid propagation of a few dominant cracks into distributed microcracking. The crack‐growth slope decreases markedly with increasing SEBS loading and film thickness, while the steady‐state fracture energy rises by a factor of ~5 across the investigated composition and thickness range. Crack‐tip microscopy and numerical simulations further reveal progressively enhanced crack blunting, tortuous crack paths, distributed deformation, and stress redistribution. These results demonstrate that crack initiation and crack propagation should be evaluated separately in stretchable photovoltaic films. Crack‐growth slope, steady‐state fracture energy, crack‐tip morphology, and stress redistribution provide complementary descriptors for assessing damage tolerance and for guiding the design of mechanically reliable stretchable organic photovoltaic materials.