Efficient Dual Mechanisms Boost the Efficiency of Ternary Solar Cells with Two Compatible Polymer Donors to Exceed 19

Ternary strategyopens a simple avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The introduction of wide bandgap polymer donors (PDs) as third component canbetter utilize sunlight and improve the mechanical and thermal stability of active layer. However, efficient ternary OSCs (TOSCs) with two PDs are rarely reported due to inferior compatibility and shortage of efficient PDs match with acceptors. Herein, two PDs‐(PBB‐F and PBB‐Cl) are adopted in the dual‐PDs ternary systems to explore the underlying mechanisms and improve their photovoltaic performance. The findings demonstrate that the third components exhibit excellent miscibility with PM6 and are embedded in the host donor to form alloy‐like phase. A more profound mechanism for enhancing efficiency through dual mechanisms, that are the guest energy transfer to PM6 and charge transport at the donor/acceptor interface, has been proposed. Consequently, the PM6:PBB‐Cl:BTP‐eC9 TOSCs achieve PCE of over 19%. Furthermore, the TOSCs exhibit better thermal stability than that of binary OSCs due to the reduction in spatial site resistance resulting from a more tightly entangled long‐chain structure. This work not only provides an effective approach to fabricate high‐performance TOSCs, but also demonstrates the importance of developing dual compatible PD materials. The ternary strategy has attracted tremendous interest due to its versatile advantages for improving the performance of organic solar cells. In this work, two polymer donors based ternary organic solar cells are prepared to achieve both high power conversion efficiency (over 19%) and long thermal stability. This study proposes the collaborative regulation of two critical driving forces mechanisms for constructing high‐performance ternary organic solar cells.