Simultaneously Decreasing the Bandgap and Voc Loss in Efficient Ternary Organic Solar Cells

Abstract Ternary architecture is a promising strategy to further boost the performance of organic solar cells (OSCs). Reducing the bandgap of the active layer materials not only widens the absorption wavelength range and enhances the short‐circuit current ( J sc ) of the OSC, but also decreases the open‐circuit voltage ( V oc ) of the device, leading to a trade‐off situation for the optimization of the material system. Herein, a small‐molecule donor BTID‐2F, featuring a narrower bandgap than that of PM6, is introduced into a PM6:Y6 based system. The redshift in external quantum efficiency indicates the narrower bandgap and better aggregation in the ternary blends than those of binary ones. Interestingly, lower energy disorder and energy loss are also attained for the ternary devices, leading to higher V oc . Furthermore, owing to the suppressed recombination and morphological optimization, a simultaneous enhancement in the J sc and fill factor boosts the power conversion efficiency (PCE) of ternary OSC to 17.9% compared to 16.62% for the binary device. Likewise, replacing the acceptor with the L8‐BO molecule further improves the ternary PCE to 18.52%. This work indicates an emerging approach for fabricating high‐performance ternary OSCs with a decreased bandgap and increased V oc .