Dielectric Properties of Nanostructured ZnO Using Impedance Spectroscopy*

Nanostructured ZnO has been investigated as an n-type semiconductor for third-generation photovoltaics. In this study, we focus on the dielectric, and in turn the optical properties of 21.9 nm spherical ZnO nanoparticles at room temperature, in both powder form and suspension in a liquid. The dielectric properties determined from this method can then be used to model a nanomaterial's optical absorption properties in photovoltaics or other electronic devices. Impedance spectra in the frequency range of 100Hz-5.1 MHz were used to investigate the frequency-dependent dielectric properties of ZnO nanoparticles. ZnO particles used in this study were suspended in variable volume fractions up to ~1% in deionized (DI) water and unrefined organic coconut oil and sonicated for variable durations before and during the experiment. Small volumes of the resulting suspension were injected sequentially into a dielectric cell for measuring frequency response. Dry particle tests were also conducted similarly. Impedance data suggests that the dielectric behavior of ZnO in a host fluid is highly dependent on sonication before and during the test, is a much stronger dipole in more polar fluids, and has a perceived dielectric constant much larger in a suspension than as a dry particle.