Sanghwa Yoon

Spalling of a Thin Si Layer by Electrodeposit-Assisted Stripping

A major goal in solar cell research is to reduce the cost of the final module. Reducing the thickness of the crystalline silicon substrate to several tens of micrometers can reduce material costs. In this work, we describe the electrodeposition of a Ni–P alloy, which induces high stress in the silicon substrate at room temperature. The induced stress enables lift-off of the thin-film silicon substrate. After lift-off of the thin Si film, the mother substrate can be reused, reducing material costs. Moreover, the low-temperature process expected to be improved Si substrate quality.

Manipulation of cuprous oxide surfaces for improving their photocatalytic activity

Manipulating the surface characteristics of metal oxide electrodes allows the properties of the interface between electrodes and the electrolyte to be controlled and can lead to improvements in both efficiency and reliability of the electrodes. In this study, the facets exposed on the surfaces of Cu2O photoelectrodes were manipulated by controlling the pH of the bath during Cu2O film electrodeposition. The Cu2O film with (100)-type facets, deposited at a bath pH of 12, produced a photocurrent 19 times higher than that of the film deposited at pH 8.3 and possessing (111) facets. In addition, inverse-opal-structured Cu2O films were electrodeposited in alkali solutions using templates of polystyrene beads; these films exhibited even higher photocatalytic activities than the planar ones. The templated, three-dimensional (3D) Cu2O film deposited at pH 12 produced a photocurrent 2.14 times higher than that generated by the planar Cu2O film deposited at the same pH; this was a result of the greater surface area and higher light absorption of the 3D film.

Oxygen Re-adsorption of a Single ZnO Nanobridge by Joule Heating under Ultraviolet Illumination

Joule heating in ZnO nanowires is known to enhance surface reactions, including oxidation and reduction. The UV sensing behaviors of ZnO nanobridges were investigated in air and Ar ambient to study the effects of Joule heating caused by the absorption of oxygen molecules. When placed under UV illumination in air ambient, the conductance of the ZnO nanobridge decreased over a specific voltage range, while the conductance increased under similar conditions when placed in Ar ambient. Our results suggest a model of oxygen molecule absorption behaviors that is facilitated through the incorporation of Joule heating.

The influence of polarity of electrodeposited Cu2O thin films on the photoelectrochemical performance

Both polar and non-polar Cu2O thin films were electrodeposited in electrolytes of different pH, and their photoelectrochemical activities in water were analyzed. The surface morphology of these tailored-polarity Cu2O films was analyzed by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), and their photoactivity was characterized through photoluminescence and Mott–Schottky measurement of the defect structure, diffusion length, carrier concentration, and charge separation. Through this, the tetrahedral surface morphology of a polar Cu2O thin film was found to exhibit a higher photocurrent in the visible spectrum than the pyramidal surface morphology of a non-polar Cu2O film. Furthermore, the higher flat-band potential and carrier concentration identified in the polar Cu2O by Mott–Schottky analysis was found to result in a higher charge separation.