Conjugated donor-acceptor star molecules: A new concept for substantial dielectric breakdown strength improvement in PVDF films

The formation of interfacial deep-level traps in the polymer matrix presents an opportunity to enhance the dielectric breakdown strength (BDS) of high dielectric constant in electrically insulative PVDF films. In this work, star-shaped donor-acceptor (D-A) molecules (S1, S2 and S3) with three electron-donating arms surrounding an electron-accepting core are incorporated into PVDF-t films using a facile solution casting process. It is found that the DC electrical insulation of the fabricated films is remarkably improved with the additive introduction. An outstanding BDS enhancement of 27% is achieved by PVDF/S3 films with 0.1 wt% of adding content. Analysis using displacement-electric (D-E) field hysteresis loops reveals that there is notable reduction of carrier density in polymer films under a high electric field. It is believed that D-A molecules serve as effective traps to capture highly energetic carriers, resulting in the dielectric breakdown occurring at a higher level. Our findings present that D-A molecules can be a new family of additive candidates for PVDF-t dielectrics to achieve improved electrical insulation.