High-k Lead-Free Ferroelectric KNN as an Electron Blocking Layer toward Efficient Hybrid Piezoelectric–Triboelectric Nanogenerators

Lead-free ferroelectric one-dimensional nanostructures exhibit great potential in building micro/nanoenergy harvesters owing to their high dielectric constant and piezoelectric properties. Herein, potassium sodium niobate (KNN) nanostructures are embedded into a poly(dimethylsiloxane) (PDMS) film to develop a hybrid piezoelectric–triboelectric nanogenerator (PTENG) that scavenges mechanical energy efficiently. By comparing different structures with and w/o the functional KNN layer, the spontaneous polarized electric field produced by the KNN-Mn film is systematically investigated, and its function as an electron blocking layer to hinder electron transfer is also well illustrated. Furthermore, after embedding KNN-Ca nanorods into PDMS to enhance relative permittivity, we find that the induced polarized electric field initiated by KNN-Ca nanorods binds free electrons and acts as a charge retention transition layer to further boost surface charge density. This work brings ideas to prepare high-performance PTENGs by applying ferroelectric materials with high permittivity.