Patterned microlens array for efficiency improvement of small-pixelated organic light-emitting devices

Abstract

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.

P‐44: Patterned Microlens‐Array Films Assisted with Auxiliary Electrodes for Luminance Improvement in Large‐Area OLEDs

“…The pixel-partition method which divides the large pixel into smaller series-connected ones can alleviate these problems and avoid the catastrophic short-circuit defects [5]. Furthermore, except for the electrical improvement shown by the literature [2][3][4], we also proved that the large-emitting-area OLED with the pixel-partition and patterned or center-hollowed microlens-array films (MAFs) [6] will be even more efficient in luminance and luminous power according to our simulation results [7].…”

Emission Characteristics of Organic Light-Emitting Diodes and Organic Thin-Films with Planar and Corrugated Structures

“…For coupling out the light smaller than the critical angle, the microlenses are partially removed, which is called “hollow structure” [89]. By removing the microlenses in the emitting layer region, the luminous efficiency can be greatly improved.…”

P‐152: Emitter‐Apodization‐Dependent Angular Luminance Enhancement of Microlens‐Array Film Attached OLED Devices

“…After MAF attachment, the normal direction luminous intensity of sample B even down to 64% of the device without the MAF due to the light trapping phenomenon by the microlens edge [14].…”

“…In addition, the microlenses of the MAF in ray-tracing program are 10 μm in diameter, 3.8 μm in height and rectangular-arranged with gaps of 2.5 μm and these parameters were confirmed by SEM measurements. The MAF was made of transparent PET (Polyethylene terephthalate) film covered with PMMA (Polymethyl methacrylate) microlenses [14]; the refractive index of PET and PMMA applied in the program were 1.5750 and 1.4893, respectively.…”