Yeongseon Kim

Characteristics of piezoelectric ZnO/AlN−stacked flexible nanogenerators for energy harvesting applications

Flexible piezoelectric zinc oxide (ZnO)-based nanogenerators (NGs) using an aluminum nitride (AlN) interlayer are proposed for high-efficiency energy harvesting applications. The effects of the AlN interlayer on device performance are studied. Use of the AlN interlayer in ZnO-based vertically integrated NGs (VINGs) results in a significant improvement in terms of the magnitude of the output voltages of up to 200 times when compared with a ZnO-based VING without any AlN interlayer. The improved device energy conversion efficiency is mainly attributed to a high contact potential barrier that the AlN interlayer provides in VINGs, along with the relatively high dielectric constant and large Youngs modulus of the AlN material. In addition, the effects of AlN thickness on the electric potential and device performance of the VINGs are investigated through observation of the output voltages of ZnO-based VINGs with thickness/position-controlled AlN interlayers. Our findings in this work are expected to provide effective and useful approaches for realizing highly energy-efficient ZnO-based NGs and their extended applications, including self-power sources and sensor devices.

Oxidation and sublimation suppression of PbTe thermoelectric legs by plasma coated ceramic layers

Plasma sprayed ceramic coating layers were investigated for use in suppressing the oxidation and sublimation of intermediate temperature PbTe thermoelectric legs (usually operated in the temperature range of 300–700 °C). The authors used two different oxides for the comparison of their antioxidation characteristics. One is yttria (Y2O3) and the other is 8 mol. % yttria-stabilized zirconia [(Y2O3)0.08(ZrO2)0.92, YSZ]. Both oxides were coated by plasma spray method on the surfaces of the PbTe thermoelectric legs, respectively. As a result, the Y2O3 coating layers could not prevent the progression of oxidation in the thermoelectric PbTe surfaces at 500 °C, but the YSZ coating layers showed a relatively high resistance enough to prevent the progression of oxidation, which is promising for intermediate-temperature thermoelectric modules. The x-ray diffraction and x-ray photoelectron spectroscopy investigations revealed that the YSZ-coating of PbTe thermoelectric legs led to the formation of the secondary oxide...

Flexible piezoelectric ZnO nanogenerator with silver-based electrode

As a possible solution for the cost-effective electrode formation of flexible piezoelectric ZnO nanogenerators, silver-based electrodes are chosen and investigated. The four types of silver-based top-electrodes are fabricated on ZnO thin films by different process conditions or techniques. Results show that the local oxidation of silver-based electrodes in the flexible piezoelectric ZnO nonogenerators can lead to a significant improvement of the device performance in terms of the output voltages. In addition, the ZnO nanogenerators with silver-paste printed top-electrodes, which can be fabricated in a simple and cost-effective way, show a considerably high output performance.