U ‐Shaped Dimeric Acceptors for Balancing Efficiency and Stability in Organic Solar Cells

Abstract Despite significant improvements in power conversion efficiencies (PCEs) of organic solar cells (OSCs), achieving excellent stability remains a great challenge to their commercial feasibility. Here, U ‐shaped dimeric acceptors (5‐IDT and 6‐IDT) with different molecular lengths are introduced into the binary OSCs as a third component, respectively. The introduction of the third component effectively reduces the energetic disorder and non‐radiative voltage losses and improves the exciton dissociation and charge transport of the devices. Consequently, the PCEs of the 6‐IDT‐ and 5‐IDT‐treated OSCs are significantly improved to 19.32% and 19.96%, respectively, which is the highest PCE for oligomeric acceptors‐based ternary OSCs to date. Meanwhile, the thermal stability of the treated devices is dramatically improved, with the initial efficiency retention of the 6‐IDT‐ and 5‐IDT‐treated devices increasing from 18% to 32% and 75%, respectively, after 1000 h of thermal stress. This is mainly attributed to the ability of the smaller molecular length of 5‐IDT to stabilize the phase‐separated morphology of the polymeric donor and small molecular acceptor, rather than the high glass transition temperature and low diffusion coefficient.