Alkoxy substitution on IDT-Series and Y-Series non-fullerene acceptors yielding highly efficient organic solar cells

In this work, we attempt to figure out alkoxy-substitution effects on two kinds of well-known non-fullerene acceptors (NFAs), IDT-series and Y-series acceptors, by placing alkoxy side chains on the β-positions of the outer thiophene units. The resulting molecules, namedIDTN-OandY6-O, exhibit different properties compared to the original acceptors namedIDTNandY6. The HOMO and LUMO levels ofIDTN-Oare slightly upshifted at the same time, which causes a slightly higher open-circuit voltage (V_oc) without sacrificing the short-circuit current density (J_sc) of the devices.J71:IDTN-Oblend films can also achieve a better blend morphology due to the conformational locking effect and higher dipole moment induced by the alkoxy groups, which helps achieve a higher fill factor (FF). In addition,Y6-Oexhibits significantly upshifted LUMO levels compared toY6, leading to a highV_ocof 0.95 V.PM6:Y6-Oblend films can also maintain an optimal blend morphology through side-chain engineering, which leads to an excellent FF of 78.0%. As a result of alkoxy substitution, bothIDTN-OandY6-O-based devices can achieve better performances of 12.1% and 16.6% thanIDTNandY6-based devices (10.9% and 15.7%), which indicates that this is an effective method to optimize these two types of NFAs.