A rare efficiency roller coaster phenomenon in ternary organic photovoltaic blends constructed from completely non-fused ring acceptors

Abstract

The ternary strategy has become one of the most effective and versatile approaches for improving the power conversion efficiency (PCE) of organic photovoltaics (OPVs). Although numerous studies have reported significant performance improvements, little attention has been paid to the unusual phenomenon of PCE loss observed at specific blend compositions during ternary optimization. Herein, we present a unique case of a “PCE roller coaster” behavior in a ternary OPV system composed of two completely non-fused ring acceptors by systematically varying their ratios. Comprehensive investigations combining device physics and morphological analyses reveal that the physical interaction between the two acceptors and the donor polymer critically governs energy alignment or misalignment, driven by the morphology-dependent variations in donor-acceptor contact types. The resulting morphology further dictates whether cascaded charge transfer or carrier trapping dominates in the ternary blend, thereby influencing charge collection efficiency. Beyond achieving improved PCE in the optimized ternary system, this study provides in-depth insight into the mechanisms underlying efficiency fluctuations, offering valuable guidance for the rational design and future development of ternary OPV systems.