Understanding the molecular mechanisms of the differences in the efficiency and stability of all-polymer solar cells

Abstract

In spite of the great success of all-polymer solar cells (all-PSCs) in terms of device efficiency mainly owing to the vigorous development of polymer donors (P_Ds) and polymer acceptors (P_As), the synergistic effects of the molecular structure and molecular weight (M_w) of P_D and P_A materials as well as P_D–P_A pair miscibility on device performance are still unclear and rarely reported. Herein, we introduced PBDB-T and its congener materials (PM6 and PM7) as P_Ds with comparable M_ws and two PYT batches as P_As with different M_ws (PYT-M and PYT-H) to deeply investigate the effects of molecular mechanisms on the device efficiency and stability in these six systems. Benefiting from proper P_D–P_A miscibility owing to the matched molecular structure and M_ws, both PBDB-T:PYT-H and PM6:PYT-M systems with suitable phase separation show comparable device efficiencies, which are much better than those of the other four all-polymer systems. Impressively, further investigation demonstrates that the PBDB-T:PYT-H active layer is more stable than the PM6:PYT-M one, resulting from the trade-offs between molecular miscibility and M_w. This work not only employs the synergetic effect of the molecular structure and molecular weight on device efficiency and stability but also provides a promising strategy to simultaneously improve the device performance of all-PSCs.