An in situ crosslinked matrix enables efficient and mechanically robust organic solar cells with frozen nano-morphology and superior deformability

Abstract

Flexible organic solar cells (F-OSCs) with excellent mechanical robustness and high performance are in high demand for their applications in wearable devices. However, considering their high-power conversion efficiency, achieving mechanical deformation stability is a significant challenge. In this study, we developed a crosslinking monomer, thioctic acid (TA) constituting dynamic covalent disulfide and H-bonds, which induces in situ cross-linking in the active layer to precisely control the molecular packing, phase separation, and the nano-morphology of the resultant film. The dynamic covalent bond exchange in the interpenetrating network dissipates the mechanical stress even under large deformations, resulting in robust blend films. The hydrogen bonding interactions freeze the nano-morphology, limiting the formation and spreading of cracks. The crack-onset strain of the optimal TA-doped PM6 : D18-2F:BTP-eC9 film was 76.58% higher than that of the PM6 : BTP-eC9 binary film. Moreover, we observed a stabilized PCE of 19.84% (certified value = 19.5%) in a rigid device and an excellent PCE of 18.32% in F-OSCs, which is the highest reported value for a flexible device to date. The optimal F-OSC exhibited excellent mechanical tolerance with 96% PCE retention after 5000 bending cycles. These results highlight the potential of our in situ crosslinking matrix strategy for realizing high-performance F-OSCs with ultrahigh mechanical robustness.