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

Abstract Ternary strategy, introducing a third component into binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). It is worth noting that the introduction of wide bandgap polymer donors (PDs) as the third component can not only better utilize sunlight but also has the potential to improve the mechanical and thermal stability of the active layer. However, efficient ternary OSCs (TOSCs) with two PDs are rarely reported due to the inferior compatibility of polymers and shortage of efficient PDs to match with non‐fullerene acceptors. Herein, two PDs with different end‐group elements (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, which plays a crucial role in optimizing film morphology. 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 impressive 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. This article is protected by copyright. All rights reserved