Piezoelectric energy harvesters (PEHs) have attracted significant attention with the ability of converting mechanical energy into electrical energy and power the self-powered microelectronic components. Generally, material's superior energy harvesting performance is closely related to its high transduction coefficient (d₃₃×g₃₃), which is dependent on higher piezoelectric coefficient d₃₃ and lower dielectric constant ε_r of materials. However, the high d₃₃ and low ε_r are difficult to be simultaneously achieved in piezoelectric ceramics. Herein, lead zirconate titanate (PZT) based piezoelectric composites with vertically aligned microchannel structure are constructed by phase-inversion method. The polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) are mixed as fillers to fabricate PZT/PVDF&CNTs composites. The unique structure and uniformly distributed CNTs network enhance the polarization and thus improve the d₃₃. The PVDF filler effectively reduce the ε_r. As a consequence, the excellent piezoelectric coefficient (d₃₃ = 595 pC/N) and relatively low dielectric constant (ε_r = 1,603) were obtained in PZT/PVDF&CNTs composites, which generated an ultra-high d₃₃×g₃₃ of 24,942 × 10⁻¹⁵ m²/N. Therefore, the PZT/PVDF&CNTs piezoelectric composites achieve excellent energy harvesting performance (output voltage: 66 V, short current: 39.22 μA, and power density: 1.25 μW/mm²). Our strategy effectively boosts the performance of piezoelectric-polymer composites, which has certain guiding significance for design of energy harvesters.

Piezoelectric energy harvesters (PEHs) fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy. The high piezoelectric charge coefficient (d₃₃) and large piezoelectric voltage coefficient (g₃₃) are key factors for the high-performance PEHs. However, high d₃₃ and large g₃₃ are difficult to simultaneously achieve with respect to $g_{33}=d_{33}/({\epsilon }_0{\epsilon }_{\text{r}})$ and $d_{33}=2Q{\epsilon }_0{\epsilon }_{\text{r}}{P}_{\text{r}}$. Herein, the energy harvesting performance is optimized by tailoring the CaZrO₃ content in (0.964-x)(K_0.52Na_0.48)(Nb_0.96Sb_0.04)O₃ -0.036(Bi_0.5Na_0.5)ZrO₃-xCaZrO₃ ceramics. First, the doping CaZrO₃ could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering, and thus reduce the domain size to ~30 nm for x = 0.006 sample. The nanodomains switch easily to external electric field, resulting in large polarization. Second, the rhombohedral-orthorhombic-tetragonal phases coexist in x = 0.006 sample, which reduces the polarization anisotropy and thus improves the piezoelectric properties. The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d₃₃ (354 pC/N). Furthermore, the dielectric relative permittivity (ε_r) reduces monotonously as the CaZrO₃ content increases due to the relatively low ion polarizability of Ca²⁺ and Zr⁴⁺. As a result, the optimized energy conversion coefficient (d₃₃ × g₃₃, 5508 × 10^-15 m²/N) is achieved for x = 0.006 sample. Most importantly, the assembled PEH with the optimal specimen shows the excellent output power (~48 μW) and lights up 45 red commercial light-emitting diodes (LEDs). This work demonstrates that tailoring ferroelectric/relaxor behavior in (K,Na)NbO₃-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.