Correlating Aggregation Ability of Polymer Donors with Film Formation Kinetics for Organic Solar Cells with Improved Efficiency and Processability

Film formation kinetics significantly impact molecular processability and power conversion efficiency (PCE) of organic solar cells. Here, two ternary random copolymerization polymers are reported, D18─N‐p and D18─N‐m, to modulate the aggregation ability of D18 by introducing trifluoromethyl‐substituted pyridine unit at para‐ and meta‐positions, respectively. The introduction of pyridine unit significantly reduces material aggregation ability and adjusts the interactions with acceptor L8‐BO, thereby leading to largely changed film formation kinetics with earlier phase separation and longer film formation times, which enlarge fiber sizes in blend films and improve carrier generation and transport. As a result, D18─N‐p with moderate aggregation ability delivers a high PCE of 18.82% with L8‐BO, which is further improved to 19.45% via interface engineering. Despite the slightly inferior small area device performances, D18─N‐m shows improved solubility, which inspires to adjust the ratio of meta‐trifluoromethyl pyridine carefully and obtain a polymer donor D18─N‐m‐10 with good solubility in nonhalogenated solvent o‐xylene. High PCEs of 13.07% and 12.43% in 1 cm2 device and 43 cm2 module fabricated with slot‐die coating method are achieved based on D18─N‐m‐10:L8‐BO blends. This work emphasizes film formation kinetics optimization in device fabrication via aggregation ability modulation of polymer donors for efficient devices. Two trifluoromethyl‐substituted pyridine units are introduced into D18 to synthesize two terpolymers with modulated aggregation abilities. Earlier phase separation and longer film formation times are achieved and lead to superior blend film morphology, resulting in efficiencies of 19.45%, 13.07%, and 12.43% in small area organic solar cell device, 1 cm2 flexible device, and 43 cm2 module fabricated by slot‐die coating.