BK 사업단에서 알려드립니다 .

 

우리 사업단에서는 전자공학과 윤태훈 교수님의 초청으로 한밭대학교의 최윤석 교수님 , 한양대학교의 유창재 교수님을 모시고 세미나를 개최합니다 .

 

관심 있는 분들의 많은 참여 부탁 드립니다 .

 

- 일시 : 2016 년 6 월 9 일 ( 목 ) 오전 11 시

- 장소 : 기전관 9401 호

- 연사 : 최윤석 ( 한밭대학교 교수 )

- 주제 : Development of Functional Nano-particle Layer for Highly Efficient OLED

- Abstract : Organic light-emitting devices (OLEDs) recently has gathered much attraction for the display application as well as lighting system. However, since OLEDs is composed of many layers considerable loss occurs when passing through the he multi-layer thin film structure. The typical light loss is approximately 80% which means only 20% of light is going through the outside of the device. To solve this problem, optical out-coupling technology is necessary to derive a lot of light from the device. The light extraction technology can be categorized as an internal extraction or an external extraction technique by the position of light extraction structure. In this research, we focused internal extraction technology because it has more merits such as high luminous efficiency y, wide viewing angle and thinner structure.

In this research, we have studied the effect of a functional internal light extraction layer to increase the light extraction efficiency of OLEDs. Metal oxide nano-particle was mixed with polymer matrix to form the well-dispersed nano-particle layer on the glass substrate first. The light scattering effect of this nano-particle layer can increase the light efficiency of OLEDs by changing the optical path of light which normally go outside of the device due to wave guide effect or total internal reflection. Several nanoparticle and polymer matrix were adopted to make a functional nanoparticle layer and they showed good scattering properties which results in the high efficiency of OLED structure.

 

- 일시 : 2016 년 6 월 9 일 ( 목 ) 오후 2 시

- 장소 : 기전관 9401 호

- 연사 : 유창재 ( 한양대학교 교수 )- 주제 : Alignment of Uniform Lying Helix Mode : Effect of Pretilt and Anchoring Energy

- Abstract : The uniformly lying helix (ULH) structure in a short pitch cholesteric liquid crystal (CLC) has attracted much attention in display applications because of their fast switching speed and continuous in-plane rotation of the optic axis based on the flexoelectro-optic effect. However, the ULH texture is not a stable configuration of the CLC within the sandwiched substrates with planar alignment layer due to its energetically stable Grandjean (standing helix) configuration. To obtain the stable ULH texture, various approaches, such as the periodic alignment patterning on a length scale comparable to the CLC pitch, the unidirectional grooved surfaces, the polymer-stabilization of the ULH texture, and the twisted configuration, were introduced. However, most approaches are impractical on a large scale except for the twisted configuration. In addition, no quantitative investigation of the formation of the ULH configuration about various cell conditions has been explored yet.

In this seminar, we quantitatively investigate the effects of the pretilt angle and the anchoring energy on the formation of the ULH texture by introducing the spatial averaged reflectance. The reflectance of the short pitch CLC cell is mainly governed by the planar CLC texture (Grandjean configuration) due to their selective reflection. On the other hand, the incident light passes through the ULH regions without selective reflection. As a result, the spatial average of the reflectance directly represents the ratio of the ULH region to the planar CLC region. That is, the lower reflectance means that the ULH texture is formed in the larger area. Finally, we found that the higher pretilt angle and the weaker anchoring energy, the better the ULH texture obtained. Also, better uniformity of the optic axis in the ULH texture was achieved in the higher pretilt sample at the same anchoring energy.