Piezoelectricity in two-dimensional covalent organic frameworks

First-principles calculations were used to investigate piezoelectricity in two-dimensional covalent organic frameworks, including those composed of C9H3N3 and C6H3B3O3 monolayers. We mainly studied the elastic stiffness constants and piezoelectric tensors of these networks using their clamped-ion and relaxed-ion components. Our results show that both of these organic materials are piezoelectric along the armchair direction because of their noncentrosymmetric structures. The strain effects on the bandgaps of these monolayers have almost no effect on their piezoelectric performance. Additionally, the dynamic stabilities of the C9H3N3 and C6H3B3O3 monolayers were examined. Despite their low piezoelectric coefficients, the piezoelectricity in these two-dimensional covalent organic frameworks is promising for applications such as biocompatible nanoelectromechanical systems because they offer potential for enhanced biocompatibility when compared with inorganic materials.