Flexible SpacerUnits Enhance 3D Terpolymer Acceptors’Optoelectronic Performance in Rigid and Flexible Devices

Designing high-performance, mechanically stable, all-polymer solar cells (all-PSCs) is crucial for their effective use in flexible and stretchable electronic devices. In this work, we developed three-dimensional polymer acceptors H6, H7, and H8 by introducing a nonconjugated flexible alkyl chain strategy to achieve efficiency and mechanical robustness in all-PSCs. Thanks to an appropriate amount of flexible space unit [flexible spacer (FS)] incorporation, improved solubility, and suppression of the excessive aggregation of the blend film, the PM:H7 device based on 5% FS acquired a remarkable 16.25% power conversion efficiency (PCE), higher than the PM6:H6 device (PCE = 15.10%) without FS units and the PM6:H8 device (PCE = 16.17%) with 10% FS units. Furthermore, we fabricated the intrinsically stretchable all-PSCs to evaluate the device’s mechanical stability and ductility. As a consequence, the H7-based all-PSCs exhibited an encouraging PCE up to 15.22% and excellent mechanical stretchability with a crack-onset strain = 12.31%. Our findings suggest that incorporating FS is an effective strategy for enhancing the mechanical robustness of conjugated polymer films, highlighting significant potential for applications in wearable devices.