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

Film formation kinetics significantly impact the molecular processability and power conversion efficiency (PCE) of organic solar cells (OSCs). In this article, we report two kinds of ternary random copolymerization polymers, D18-N-p and D18-N-m, to modulate the aggregation ability of the conventional polymer donor D18 by introducing trifluoromethyl substituted pyridine unit at para- and meta-position, respectively. The introduction of the pyridine unit significantly reduced material aggregation ability and adjusted the interactions with acceptor L8-BO, thereby leading to largely changed film formation kinetics with earlier phase separation and longer film formation times, which enlarged fiber sizes in blend films and improved carrier generation and transport. As a result, D18-N-p with moderate aggregation ability delivered a high PCE of 18.82% by pairing with L8-BO, which was further improved to 19.45% via interface engineering. Despite the slightly inferior small area device performances, D18-N-m showed improved solubility, which inspired us to adjust the ratio of meta-trifluoromethyl pyridine carefully and obtain a polymer donor D18-N-m-10 with good solubility in non-halogenated 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 were achieved based on D18-N-m-10: L8-BO blends. Our work emphasizes film formation kinetics optimization in device fabrication via aggregation ability modulation of polymer donors for efficient devices. This article is protected by copyright. All rights reserved.