Promoting efficiency, deformability, and life expectancy of stretchable organic solar cells (OSCs) have always been key concerns that researchers are committed to solving. However, how to improve them simultaneously remains challenging, as morphology parameters, such as ordered molecular arrangement, beneficial for highly efficient devices actually limits mechanical stability and deformability. In this study, the unfavorable trade‐off among these properties has been reconciled in an all‐polymer model system utilizing a mechanically deformable guest component. The success of this strategy stems from introducing a highly ductile component without compromising the pristine optimized morphology. Preferable interaction between two donors can maintain the fiber‐like structure while enhancing the photocurrent to improve efficiency. Morphology evolution detected via grazing incidence X‐ray scattering and in situ UV–vis absorption spectra during stretching have verified the critical role of strengthened interaction on stabilizing morphology against external forces. The strengthened interaction also benefits thermal stability, enabling the ternary films with small efficiency degradation after heating 1500 h under 80 °C. This work highlights the effect of morphology evolution on mechanical stability and provides new insights from the view of intermolecular interaction to fabricate highly efficient, stable, and stretchable/wearable OSCs. The intermolecular interaction in an all‐polymer system is well modulated through incorporating a third component, resulting simultaneous enhancement of efficiency, deformability, and mechanical stability. Better mechanical stability against multiple forces in optimized ternary system is achieved through strengthening intermolecular interaction between two donors to inhibit the morphology evolution under strain.