Film Formation Kinetics of Polymer Donor and Nonfullerene Acceptor Active Layers During Printing Out of 1,2,4‐Trimethylbenzene in Ambient Conditions

Abstract

Slot‐die coating is a promising upscaling fabrication method to promote commercialization in the field of organic solar cells. Herein, the nonfullerene active layer blend of a conjugated polymer PffBT4T‐2OD and a small molecule acceptor EH‐IDTBR, which is printed out of the nonhalogenated solvent 1,2,4‐trimethylbenzene, is studied. The film formation kinetics of the active layer PffBT4T‐2OD:EH‐IDTBR is probed in terms of the temporal evolutions in morphology as well as molecular conformation and aggregation as revealed by in situ grazing‐incidence small angle X‐ray scattering and UV–vis spectroscopy during the film printing process. A five‐regime mesoscale domain growth process is observed in the active layer from the liquid state to the final dry state. The solvent evaporation‐induced domain growth is accompanied with molecular stacking in a distinct J‐type aggregation of the acceptor and a slight H‐type aggregation of the donor molecules. The printed active layers exhibit an edge‐on dominated PffBT4T‐2OD and a face‐on dominated EH‐IDTBR crystallite structure. Compared to the neat PffBT4T‐2OD and EH‐IDTBR films, in the active layer, the crystallite structure deviates slightly in lattice spacing.