High-Molecular-Weight Electroactive Polymer Additives for Simultaneous Enhancement of Photovoltaic Efficiency and Mechanical Robustness in High-Performance Polymer Solar Cells.

The development of small-molecule acceptors (SMAs) has significantly enhanced the power conversion efficiency (PCE) of polymer solar cells (PSCs); however, the inferior mechanical properties of SMA-based PSCs often limit their long-term stability and application in wearable power generators. Herein, we demonstrate a simple and effective strategy for enhancing the mechanical robustness and PCE of PSCs by incorporating a high-molecular-weight (MW) polymer acceptor (P A, P(NDI2OD-T2)). The addition of 10-20 wt % P A leads to a more than 4-fold increase in the mechanical ductility of the SMA-based PSCs in terms of the crack onset strain (COS). At the same time, the incorporation of P A into the active layer improves the charge transport and recombination properties, increasing the PCE of the PSC from 14.6 to 15.4%. The added P As act as tie molecules, providing mechanical and electrical bridges between adjacent domains of SMAs. Thus, for the first time, we produce highly efficient and mechanically robust PSCs with a 15% PCE and 10% COS at the same time, thereby demonstrating their great potential as stretchable or wearable power generators. To understand the origin of the dual enhancements realized by P A, we investigate the influence of the P A content on electrical, structural, and morphological properties of the PSCs.