Controlling Rigidity of The Conjugated Backbone Using Plasticizing Molecular Additives to Enhance Deformability in Organic Semiconductors

Plastic electronics, featuring deformable polymer layers, have emerged as a promising technology in recent decades. Researchers have been focused on enhancing the deformability of conjugated polymers by fine-tuning both the intrinsic molecular structure, such as the conjugation length of the polymer backbone, and the characteristics of functional side chains, including their length, branching points, and hydrogen bonding capabilities. However, it has become evident that chemical tuning alone has its limitations in overcoming the inherent trade-off relationship between electrical performance retention and mechanical deformability. To address this trade-off phenomenon, recent studies have introduced extrinsic aids into conjugated polymers, which encompass elastomeric polymers, crosslinkers, dopants, and various molecular additives. This research explores the impact of the chemical structures of plasticizing molecular additives (PMAs) on the mechanical, thermal, morphological, and electrical properties of films containing PMAs under deformation. For the purpose of a comprehensive comparison, our study employs a solution-based rheology and small-angle neutron scattering (SANS) technique to elucidate the adjusted persistence length of conjugated polymer, Poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (PDPP2T-TT-OD) interacting with various species of PMAs. Our findings reveal a significant influence of the modified persistence length of PDPP2T-TT-OD on the thin films’ mechanical deformability, as determined through pseudo-free standing tensile testing. Based on our systematic analyses, we propose that the uniform distribution of PMAs within a conjugated polymer substantially enhances the deformability of thin films. These results are anticipated to offer valuable insights into the establishment of design principles for plasticizing molecular additives in the realm of plastic electronics.