Flexible-Spacer Embedded Polymer Donors Afford Superior Blend Miscibility for High-Performance and Mechanically-Robust Organic Solar Cells

Developing organic solar cells (OSCs) with high photovoltaic performance and mechanical robustness is one of the most urgent tasks to ensure their operational reliability in wearable devices. However, it remains challenging to enhance their mechanical properties without compromising the electrical properties of high-performance active materials. Here, we develop a series of polymer donors (P_Ds), with which highly efficient OSCs having remarkable mechanical reliability are demonstrated. By interposing a controlled amount of 1,10-di(thiophen-2-yl)decane flexible spacer (FS) into a PM6 backbone, we are able to significantly enhance the intermixing of the new P_Ds with a small molecule acceptor (Y7), affording sufficient pathways for efficient charge percolation and mechanical stress dissipation. As a result, OSCs based on the P_D containing 5 mol% FS units and Y7 exhibit a high power conversion efficiency (PCE) of 17% with a crack onset strain (COS) of 12% and a cohesive fracture energy (G_c) of 2.1 J m−2, significantly outperforming reference PM6-based devices (PCE = 15%, COS = 2% and G_c = 1.0 J m−2).