All-polymer solar cells (all-PSCs) still exhibit lower power conversion efficiency (PCE) compared to fullerene-based polymer solar cells (PSCs) due to the large-scale phase separation leading to inefficient charge dissociation at donor/acceptor (D/A) interfaces. We controlled the (D/A) interfacial morphology in all-polymer blend film using a pentafluorobenzene-based additive (FPE) with quadrupolar electrostatic interactions between polymer donor and polymer acceptor. The FPE processed blend film exhibited a bicontinuous interpenetrating morphology without large-scale phase separation and an enhanced π–π stacking with face-on orientation. The morphology changes improved the charge carrier extraction and charge transport between D/A interfaces, resulted in an increase of short-circuit current (JSC) and fill factor (FF) yielding a PCE of 4.5%. The photovoltaic result using FPE additive represents a 55.2% improvement over the control device (2.9% → 4.5%).