Rational molecular design of guest acceptor for organic solar cells with 20.2% efficiency

To achieve high-efficiency organic solar cells (OSCs), the introduction of guest molecules into binary blended films (D:A system) has become the most effective method. However, the molecular design rules for guest molecules that achieve the goals by reducing voltage losses have been rarely reported. Here, guided by the molecular electrostatic potential (ESP) derived from density functional theory (DFT) calculations, we present a rationally designed guest acceptor, ANF-4, featuring very weak electrostatic interactions compared to the benchmark acceptor BTP-eC9. The larger ESP difference promotes stronger intermolecular interactions and higher miscibility. The addition of ANF-4 significantly alters the morphology of the binary system by suppressing the excessive aggregation of BTP-eC9, which leads to improved charge separation, reduced trap-assisted recombination, and efficient carrier transport. Consequently, the PM6:BTP-eC9:ANF-4-controlled device exhibits an improved radiative limit open-circuit voltage ( V OC rad) while significantly reducing non-radiative voltage loss (ΔVnr), thus achieving a remarkable increase in open circuit voltage (VOC) of 33 mV. As a result, the device produces a new benchmark power conversion efficiency (PCE) of 20.23% (certified 20.0%) with a remarkably VOC of 0.876 V. This work provides a promising way to develop efficient guest molecules, thereby pushing the OSCs technology closer to commercial application.