Synergistic Enhancement of Hybrid Piezoelectric-Triboelectric Nanogenerator via Morphological and Polarization Engineering of NaNbO ₃ Nanostructures

Hybrid piezo/triboelectric nanogenerators (H-P/TENGs) are highly effective for mechanical energy harvesting; however, while existing literature heavily focuses on traditional piezoelectric polymers or bulk binary ceramics, the specific role of lead-free filler morphology remains largely unexplored. This study addresses this gap by systematically isolating the roles of morphology and polarization using lead-free sodium niobate (NaNbO 3; NNO) nanostructures within a polydimethylsiloxane (PDMS) matrix. We evaluated four distinct geometries; nanowires, nanocubes, and their sonicated counterparts. The cubic morphologies consistently outperform wire-like structures due to their superior crystallinity and higher dielectric and piezoelectric properties. Additionally, mechanical sonication resolved the typical trade-off between filler loading and surface roughness, maximizing the effective contact area for triboelectric electrification. Kelvin probe force microscopy (KPFM) and an overlapped electron cloud model reveal that forward polarization optimizes performance by lowering the composite work function, which enhances electron transfer during contact. Under the optimal configuration of 5 wt % sonicated nanocubes and forward polarization, the device achieved a peak power density of 5.25 W/m 2 (a six-fold improvement over the pristine matrix) and successfully powered a commercial scientific calculator. These findings establish filler geometry, morphology, or any other filler-related properties as clear design rules for high-performance, lead-free hybrid nanogenerators.