The Intrinsic Role of Molecular Mass and Polydispersity Index in High-Performance Non-Fullerene Polymer Solar Cells

The degree of polymerization can cause significant changes in the blend microstructure and physical mechanism of the active layer of non-fullerene polymer solar cells, resulting in a huge difference in device performance. However, the diversity of stability issues, including photobleaching stability, storage stability, photostability, thermal stability, and mechanical stability, and more, poses a challenge for the degree of polymerization to comprehensively address the trade-off between device efficiency and stability and reasonably evaluate the application potential of polymer materials. Herein, a series of PM6 polymers with different weight-average molecular weights (M_w) and polydispersity index (PDI) are synthesized. The effects of the degree of PM6 polymerization on the efficiency and degradation behaviors of the photovoltaic systems based on Y6 as acceptor are investigated systematically. The findings regarding stability issues, together with the trade-offs in the efficiency-stability gap, formulate a complete guideline for the material design and performance evaluation in a way that relies much less on trial-and-error efforts.