Ultrahigh current output performance in piezoelectric energy harvesters enabled by phase boundary-bandgap synergistic engineering.

With the rapid expansion of the Internet of Things, piezoelectric energy harvesting has become essential for sustainable self-powered microsystems. However, achieving sufficient output current under operating conditions remains a persistent challenge. Herein, a phase-boundary and bandgap co-engineering strategy is implemented for potassium sodium niobate-based ceramics by incorporating BiFeO3 into 0.97(K0.5Na0.5)(Nb0.96Sb0.04)O3-0.03(Bi0.5Na0.5)0.85(Li0.5Nd0.5)0.15ZrO3. This induces a rhombohedral-tetragonal phase boundary that establishes nanoscale multiphase coexistence alongside an elevated average polarization displacement, enabling an exceptional piezoelectric coefficient. Simultaneously, ultralow resistivity is achieved through the lower bandgap resulting from BiFeO3 incorporation. This design achieves ultrahigh current density (50 μA/cm2) and power density (860 μW/cm3). Atomic-resolution structural analyses reveal that continuous rotation of the polarization vector, promoted by multi-directional polar states and high-density multiscale nanodomains, suppresses polarization anisotropy and domain-wall pinning, thereby synergistically amplifying piezoelectric responses. Concurrently, narrow-bandgap BiFeO3 doping elevates oxygen-vacancy concentration, lowering the conduction-band minimum and narrowing the bandgap, further reducing resistivity.