Patterned microlens array for efficiency improvement of small-pixelated organic light-emitting devices.
In this paper, we experimentally and theoretically investigated the optical characteristics of organic light-emitting devices (OLEDs), having different pixel sizes and attached with patterned microlens array films. For a regular microlens array, though it can extract the waveguiding light and increase luminous current efficiency for a large-pixelated OLED, we observed that it decreases the luminance to an even lower level than that of the planar OLED as its pixel size is close to the microlens dimension. Although a microlens can effectively outcouple the light rays originally at incident angles larger than the critical angle, it also can impede the outcoupling for the light rays originally at incident angles smaller than the critical angle. Enhancement or reduction of the light extraction depends on the relative positions of the light emitting point and the microlens. Therefore, we proposed a center-hollowed microlens array, of which the microlenses directly upon the pixel are removed, and proved that it can increase the luminous current efficiency and luminous power efficiency of a small-pixelated OLED. By attaching this patterned microlens array, 87% of luminance enhancement in the normal direction was observed for a 0.1x0.1 mm2 OLED pixel. On the other hand, a regular microlens array resulted in 4% decrease under the same condition.
Lin
Hoang-Yan
HY
Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National TaiwanUniversity, Taipei, Taiwan, Republic of China.
Ho
Yu-Hsuan
YH
Lee
Juin-Haw
JH
Chen
Kuan-Yu
KY
Fang
Jheng-Hao
JH
Hsu
Sheng-Chih
SC
Wei
Mao-Kuo
MK
Lin
Hung-Yi
HY
Tsai
Jen-Hui
JH
Wu
Tung-Chuan
TC
D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007909:Lenses; D008029:Lighting / Q000295:instrumentation*; D008904:Miniaturization; D009930:Organic Chemicals / Q000737:chemistry*; D012666:Semiconductors
D009930:Organic Chemicals