Molecular symmetry effect on the morphology and self-aggregation of semiconducting polymers

Abstract

Molecular self-aggregation and crystallization of the semiconducting polymer (SCP) are key features of organic electronic devices. In this study, we synthesized a new polymer with an asymmetrically incorporated fluorine atom in the TVT (asy-1FTVT) of a donor–acceptor type SCP (asy-PNDI1FTVT) and compared its optical and physical properties with those of two symmetric acceptor polymers (PNDITVT and PNDI2FTVT). The molecular aggregation and crystallization behavior of the newly synthesized asy-PNDI1FTVT, containing irregularities within the repeating unit, differed from those of the two symmetric polymers. Atomic force microscopy and grazing-incidence wide-angle X-ray scattering revealed much lower crystallinity of asy-PNDI1FTVT than that of the symmetric polymers. In performance tests of polymer solar cells with an inverted structure, PTB7-Th:asy-PNDI1FTVT exhibited a well-mixed morphology between the donor and acceptor polymers and efficiently facilitated the charge dissociation process, thereby enhancing the short-circuit current (J_SC) and the power conversion efficiency.