Precise Control Over Crystallization Kinetics by Combining Nucleating Agents and Plasticizers for 20.1% Efficiency Organic Solar Cells

Abstract Obtaining controllable active layer morphology plays a significant role in boosting the device performance of organic solar cells (OSCs). Herein, a quaternary strategy, which incorporates polymer donor D18‐Cl and small molecule acceptor AITC into the host D18:N3, is employed to precisely modulate crystallization kinetics for favorable morphology evolution within the active layer. In situ spectroscopic measurements during film‐formation demonstrate that while D18‐Cl works as a nucleator to promote aggregation of D18 and foster donor/acceptor intermixing, AITC has exactly the opposite impact on aggregation of N3 and intermixing kinetics of donor and acceptor, working as a plasticizer. The mutually compensational effect of the dual‐guests, as a result, enables synergistic control over fibrillar networks, multi‐length scale morphology, and vertical phase distribution, leading to optimized 3D morphology for greatly enhanced exciton dissociation and charge transfer, suppressed charge recombination, and reduced energy loss. Consequently, the quaternary OSCs based on D18:D18‐Cl:N3:AITC achieved an excellent power conversion efficiency of 20.1%, which represents one of the highest efficiencies for single‐junction OSCs. This work presents an effective strategy to precisely regulate crystallization kinetics toward advanced morphology control for high‐performance OSCs.