Piezo-enhanced Thermoelectric Properties of Highly Preferred c‑Axis ZnO Nanocrystal Films: Implications for Energy Harvesting

We propose a highly preferred c-axis-oriented but random in-plane-oriented nanocrystal to enhance the conversion of thermal to electrical energy for future energy harvesting. A highly preferred c-axis-oriented but random in-plane-oriented ZnO nanocrystal film is successfully fabricated by a homemade precursor flow rate-interrupted atomic layer deposition (ALD) system. X-ray diffraction (XRD) results identify only a (002) peak in the ZnO nanocrystal films, and azimuthal ϕ scans reveal no folded symmetry in the films, indicating a highly preferred c-axis-oriented but random in-plane structure. The Seebeck coefficient is −0.345 mV/K, and the power factor is 3.66 × 10–4 W/(m K2) at 399.65 K as the D-spacing of the (002) orientation expands to 0.421%. These observations suggest that additional electrical conductivity can be induced by the piezoelectric effect in the c-axis lattice plane of the ZnO nanocrystal film and that phonon penetration is blocked by in-plane grain boundaries.