Achieving stable organic solar cells with 19.2 % efficiency via fine interpenetrating network with fused-ring aromatic lactone donor

Abstract

The ternary strategy has enhanced the power conversion efficiency (PCE) of organic solar cells. However, long-term stability remains a challenge due to heat-induced molecular interactions and excessive self-aggregation. The fused-ring aromatic lactone (FAL) unit, with its extended molecular plane and electron-withdrawing ability, acts as an ideal building block in our newly designed donor P35. By introducing P35 into PM6:L8-BO systems, it optimizes film morphology and enhances π-π stacking, facilitating phase separation and balancing charge transport channels. The electron-withdrawing capability of P35 lowers the HOMO levels, thereby decreasing non-radiative recombination. Additionally, the extended molecular plane of P35 provides structural support to prevent the collapse of fiber-like PM6 and crosslinks with PM6 to form a thermodynamically stable interpenetrating network. This effectively limits the formation of isolated SMA islands, thereby minimizing the degeneration of the active layer. Consequently, an optimized PCE of 19.2 % (certified 18.55 %) is achieved in the PM6:P35:L8-BO devices, which still retains 80 % initial PCE under 600 h of AM 1.5 G illumination and 90 % PCE after 950 h storage in darkness. This research emphasizes the importance of electron-withdrawing capabilities and extended molecular planes in achieving long-term stability and high efficiency.