Flexible Spacer-block Multi-component Copolymerized Donors Enable Resilient Organic Solar Cells with over 40% Crack-onset Strain

Multi-component copolymerized donors (MCDs) represent an advantageous electron-donating material for optimizing the efficiency of flexible organic solar cells (f-OSCs). However, the inherent randomness in typical MCD structures often leads to non-uniform structures, thereby compromising intermolecular assembly and molecular organization. Consequently, achieving a balance between high efficiency and adequate stretchability poses a significant challenge. In this study, a novel series of sequentially-block MCDs with high molecular weight has been developed. The regular polymer skeleton and ideal molecular stacking resulting from the sequential block arrangement in the PM6-Cl_0.8-b-D18-Cl_0.2-TCl donor material led to a stabilized power conversion efficiency (PCE) of 18.55% for rigid and 17.21% for flexible binary OSCs. Additionally, promising crack-onset strain (COS) values of 32.02% and 22.58% have been observed in pristine and blend films, respectively, striking a balance between photovoltaic and mechanical properties. Notably, the PCE of the optimal ternary device based on PM6-Cl_0.8-b-D18-Cl_0.2-TCl also achieved 19.57%. Furthermore, the incorporation of the flexible functional group 1, 4-bis (thiophen-2-ylthio) butane (BTB) further enhanced the mechanical stretchability. The COS values of 40.29% and 25.38% have been obtained in flexible spacer-block MCD PM6-Cl_0.8-b-D18-Cl_0.2-BTB pristine film and corresponding blended film, respectively, marking some of the highest values achieved by MCD-based binary OSCs. This study showcases the innovative potential of sequentially-block MCDs incorporating flexible spacers in the development of high-performance and mechanically robust f-OSCs for the first time.