Unfolding the Correlation between Solution Aggregation and Solid-State Crystal Orientation in Donor-Acceptor Copolymers via Solvent Additive Processing.

Tailoring the crystal orientation of donor-acceptor (D-A) copolymers is vital for boosting the performance of optoelectronic devices. Despite recent advances in controlling the crystal orientation of D-A copolymers in thin films, the investigation into their aggregates in solution and the correlation between the solution aggregates and crystal orientation in the solid-state has been limited. Herein, we report an effective solvent additive strategy for tuning solution aggregates and the consequent solid-state structures of poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)). Specifically, the addition of 1-decanethiol (10-thiol) to the P(NDI2OD-T2) chloroform solution promoted the aggregation of P(NDI2OD-T2) chains because of the improved planarization of the main backbones, which changed their crystal orientation in the thin film from coexisting edge-on and face-on to dominant edge-on when produced by drop-casting. The mechanism of this crystal orientation transformation was elucidated based on the interaction between the 10-thiol and the alkyl side chains of P(NDI2OD-T2). The optical properties of P(NDI2OD-T2) thin films with different crystalline structures are closely correlated. Notably, the 10-thiol-enabled facile tailoring of the crystal orientation in P(NDI2OD-T2) can be readily applied to other D-A copolymers of interest. The findings of this study highlight a robust solvent additive strategy for regulating solution aggregates and crystal orientation in D-A copolymer thin films, which have applications in many optoelectronic devices. This article is protected by copyright. All rights reserved.