Developed a super wide band nonreflection nanostructure
• Posted as the front page article in the world renowned nano science magazine “Small”

 
• Professor Yong Tak LEE(left), and Mr. Young Min SONG  (PhD student)

□  A GIST research team has succeeded in developing a technology that maximizes photo element efficiency.
• The team led by professor Yong Tak LEE of the Department of Information and Communications (best pupil: PhD student Mr. Yong Min SONG) succeeded in developing a “super wide band nonreflection nanostructure” having a parabolic structure that minimizes the light reflection rate of a photo element surface.
• This research result was posted as the front cover picture article in “Small (Small, IF: 6.525l)” magazine on May 7th, 2010, a prominent academic journal in the nanoscience field. This research was supported by the “World Class University” project promoted by the Ministry of Education, Science and Technology and the National Research Foundation of Korea. 

□  This research result is meaningful in that it produced a nanostructure that could perform nonreflection characteristics in a much wider wavelength band compared to previous research results, opening opportunities to significantly increase the efficiency of a photo element.
• In order to increase the efficiency of a photo element such as solar cells and light emitting diodes, it is important to minimize the reflection of light generated from the surface of the element. In particular, semiconductor materials such as silicon and gallium arsenic have very high refractive rates compared to air, and thus have been the main reason for reducing the efficiency of photo elements, as 30–50% of light reflection occurred in the element surface. This has been the main factor inhibiting the increase in performance of photo elements.
• In order to solve this problem, a nonreflection coating method that reduces reflection by depositing multilayered thin layers on an element surface was previously used, but this could only be applied in very narrow wavelength regions and angles. In conjunction with this method, research on a method to reduce light reflection in a wide wavelength band by producing a cone shaped nanostructure, such that the reflection rate can change slowly, was conducted, and the team reported the relevant research result in “Optics Letters” last June.

 <Photo: Image of a parabolic type nonreflection nanostructure. Mimetic diagram of light reflection on a flat surface (top of the photo) and light reflection on the surface where the nonreflection nanostructure is applied (bottom of the photo). It can be seen that light reflection does not occur on the surface where nanostructure is applied.>

• In this research, the team led by Professor LEE developed an innovative method to show nonreflection characteristics in a wavelength band that is much wider than the existing cone type method by producing a parabolic type nanostructure. Although it had already been revealed that a parabolic structure can reduce the reflection rate in a wide band compared to a cone type, this research is the first to actually prove the above through practical tests.

□ The team led by Professor LEE used a process wherein a laser intervened lithography  process, reflow, and pattern replication were combined, in order to produce a parabolic type nanostructure.

 <Photo: Mimetic diagram of the method for producing a parabolic type nonreflection nanostructure. The image on the left shows laser intervened lithography, reflow, and the pattern replication method. The picture inside the box is a scanning electron microscope photo of a nanostructure according to pattern replication time.>
• This method costs less to produce nanostructures compared to the existing E-beam lithography, and also has the merit of simplifying the production technology since the parabolic type structure is produced via a simple heating process called reflow. Furthermore, it can be applied to various materials such as glass and sapphire, not only silicon and gallium arsenic, which are widely used in semiconductor photo elements including solar cells.

□  Professor Yong Tak LEE said, “This research is a meaningful research since we were able to produce a parabolic nanostructure via a very simple method that was not realizable until now, and it can be applied in wide band. Thus, if it is used in solar cells that accept much more light energy and convert it to electric energy, we could significantly reduce the amount of energy required.”
• The team actually reported the theoretical results in the February edition of the world renowned science magazine “Optic Letters,” where they stated that if the nanostructure is applied to a thin silicon solar cell, the cell efficiency could be increased by about 25% compared to the existing nonreflection coating method.
• Professor LEE also said that, “This method can be applied to not only solar cells but also to the surface of light emitting diodes and photon detectors, thereby maximizing light efficiency. And if it is applied to transparent glass, the penetration rate could be raised to 100%.”