Alkoxy Substitution on Asymmetric Conjugated Molecule Enabling over 18% Efficiency in Ternary Organic Solar Cells by Reducing Nonradiative Voltage Loss

A ternary strategy is considered to be an efficient and simple way to further enhance the performance of organic photovoltaics (OPVs). However, the "structure–performance" correlation of the third component in the ternary device has rarely been clearly understood from the aspect of the material's eigenproperties. Herein, this relationship is investigated in depth by employing three asymmetric skeleton nonfullerene acceptors as the third component in the host system of PM6:BTP-eC9, respectively. Compared with TB-S and TB-S1, the alkoxy-substituted TB-S1-O possesses a more stable planar conformation, a higher surface energy, and a larger ordered stacking domain due to the existence of noncovalent conformational locking (O···H). Consequently, the PM6:BTP-eC9:TB-S1-O device exhibits the highest efficiency of 18.14% as compared with the devices based on PM6:BTP-eC9:TB-S (16.16%) and PM6:BTP-eC9:TB-S1 (16.18%). Most interestingly, only the PM6:BTP-eC9:TB-S1-O device can maintain the positive effect of VOC improvement, because a significant reduction in nonradiative voltage loss can be observed in this device. Our systematic study reveals that alkoxy substitution on an asymmetric backbone is an efficient method to construct the third component for high-performance ternary organic solar cells.