Overview of OLED device characterization

Editor : Papilio


Overview of OLED device characterization


 As OLED display is applied to mobile phones and TV products intensively, manufacturers are making efforts to develop technologies such as performance improvement, yield increase and cost reduction. Particularly, the performance of OLED displays varies greatly depending on the organic materials used, and it is also important to develop an inexpensive product because the organic materials are expensive. The companies that supply OLED materials are the most talked about improvement of the performance of organic materials, and OLED display manufacturers are also focusing on material research to study the properties of organic materials and to select them well. In other words, it is no exaggeration to say that it is good to develop and adopt good organic materials to make OLED displays. To develop and select good organic materials, various characterization is necessary. This section provides an overview of OLED device characterization.

First, when developing or selecting an organic material to produce high quality OLED display, the product is not made and evaluated the same as the OLED display. Organic materials are expensive and are not efficient in data analysis. Therefore, in the evaluation method of organic materials for OLED display, the OLED type is specially designed for research and development. Such a form is called a unit cell (also, called TEG Cell). The design of OLED unit devices has various forms per the manufacturers, and it also makes unique design considering the structure of production equipment and structure of evaluation method. Figure 1 shows an example.


(Figure 1) OLED unit device design example (Left: PinWheel structure, Right: Line Abreast structure)


As shown in the figure, it is intended to have several light emitting surfaces on one substrate, to obtain statistical data through repeated experiments and various experiments using one sample. In addition, it is necessary to improve the properties for application products used in the development of organic materials. Particularly, the OLED can be used not only as a display product but also as a lighting product, so that a characteristic evaluation optimized for a corresponding application field is required. For example, an OLED display can display a variety of colors using three colors of R, G, and B, while OLED lighting can produce a product with only white. In the case of OLEDs for illumination, the lifetime is longer than that of display OLEDs. Due to these detailed differences, the evaluation items should be well defined and the measurement system should be configured of the intended application field when evaluating the characteristics of OLED unit devices. Figure 2 shows the performance comparison of OLED display and OLED illumination.

(Figure 2) Display OLED vs. Illumination OLED performance comparison

 I am not an expert in organic materials, but I think that if you say good organic material, it means that a lot of light comes out by applying low electricity, that is, high efficiency. In addition, it can be said that it is good product to be able to use for such a long time with high efficiency. In fact, many OLED unit devices have been evaluated in terms of efficiency and lifetime. Figure 3 shows the roadmap data related to OLED lighting efficiency and lifetime development.

(Figure 3) OLED lighting efficiency and lifetime development roadmap
(reference: OLED Technology in Lighting Applications, LpR Article | Technologies | Sep 30, 2016)

 Considering that the luminous efficiency of a fluorescent lamp used indoor is 80 ~ 100lm/W, there is considerable progress in improving the efficiency of using an OLED as a quiet product. It is necessary to develop the production side to see if it can be produced with stable yield. If stable efficiency is achieved, long-lasting products will be more attractive. LED lighting, which is now rapidly replacing fluorescent lighting, is reported to have a life span of more than 50,000 hours. Therefore, to secure competitiveness of products, it is necessary to develop lifetime improvement technology.

 It is necessary to consider the electrical, optical, and mechanical aspects basically construct the evaluation environment when evaluating the characteristics using OLED unit devices. On the electrical side, there are methods of connecting electric signals to OLED unit devices, applying electric signals, and measuring electric signals. In the optical aspect, it is necessary to establish the evaluation environment of the definition of characteristic evaluation items such as luminance, color coordinates, spectrum, efficiency, etc., as consideration for quantification of measurement values. In terms of mechanism, there are factors such as fixing, moving, and automatic evaluation of OLED unit devices. Figure 4 is a categorization of the Mcsciecne inspection technology related to OLED characterization.

(Figure 4) Classification of OLED characteristics evaluation technology (provided technology by McScience)

 McScience offers a variety of OLED characterization equipment that combines these complex evaluation techniques and provides the basis for efficient data measurement, management, and analysis by performing software-based characterization.

(Figure 5) OLED Characteristic Evaluation System