Synergistic strategy of rigid-bridge and flexible-bridge achieving high-performance and mechanical robustness all-Polymer solar cells

As the great potential of the all-polymer solar cells (all-PSCs) for wearable devices, both excellent photoelectric conversion efficiency (PCE) and mechanical robustness are essential for commercial application. Unfortunately, the current photoelectric conversion efficiency and mechanical robustness of all-PSCs are always trade-off parameters. Here, a synergistic strategy of rigid-bridge and flexible-bridge in polymerized small molecular acceptors (PSMAs) affords four polymerized acceptors PY-IT, PY-IF1, PYF1-A and PYF1-B to simultaneously improve the PCE and mechanical property of the organic solar cells (OSCs). The different molecular structures from different bridges results in different molecular stacking, energy disorder, and mechanical robustness. The rigid-bridge PY-IT-based device yields a moderate PCE of 15.07% and flexible-bridge PY-IF1-based one shows a PCE of 11.73%. The terpolymer PYF1-A with the flexible-bridges partly replacing Y units also shows unsatisfactory PCE of 13.60%. Interestingly, PYF1-B with the flexible-bridges partly replacing the rigid-bridges presents ordered molecular stacking, inducing the all-PSCs with PCE of 16.27%, which is the highest values in the flexible non-conjugated PSMAs-based devices. Besides, PM6:PYF1-B achieves an outstanding crack onset strain (COS) of 16.08% which is much better than 8.67% for PM6:PY-IT counterpart. Intrinsically flexibility enables the flexible device based on PYF1-B with preeminent bending tolerance. Besides, PM6:PYF1-B based blend shows better comprehensive performance with an efficiency stretchability factor (ESF) of 2.16%, which is almost twice than that of PM6:PY-IT counterpart. Our work provides a clear recognition about the rigid-bridges and flexible-bridges in the PSCs and promotes the development of all-PSCs in wearable electronic devices.