Ultralow loading of carbon quantum dots leading to significantly improved breakdown strength and energy density of P(VDF-TrFE-CTFE)

Abstract

Relaxor ferroelectric polymer P(VDF-TrFE-CTFE) is attracting increasing attention for electronic applications due to its high dielectric constant and relaxation characteristic. However, the low breakdown strength and premature saturation of polarization of this polymer have hampered its practical application severely. In this work, carbon quantum dots (CQDs) with functional groups and size of about 5 nm have been incorporated to overcome these issues. The nanocomposite with 0.1 wt% CQDs presents significantly improved breakdown strength and discharge energy density. Its breakdown strength (E_b) has been increased by 30.7% up to 340 kV mm⁻¹. Due to the Coulomb blockade effect, the electrons can be restrained in the deep traps, which is favorable for the improvement of breakdown strength. Besides, the abundant functional groups around CQDs are beneficial to form adequate hydrogen bonds, resulting in increased crystallinity and breakdown strength as well. Additionally, the discharge energy density has been improved by 41.7% up to 6.8 J cm⁻³. The study demonstrates the effective enhancement of breakdown strength and energy density by ultralow loading of CQDs for P(VDF-TrFE-CTFE) polymer.