1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) panel having organic EL elements arranged in a matrix on a substrate, and more particularly to such an organic EL panel which can effectively prevent moisture from entering the organic EL elements.
2. Description of Related Art
Organic EL display panels have conventionally been known as one example of flat display panels. Because, unlike liquid crystal display (LCD) panels, organic EL display panels are self emissive and because organic EL display panels are bright and clear flat display panels, their widespread use is highly expected.
An organic EL display comprises a great number of organic EL elements arranged in a matrix, and employs these organic EL elements as pixels of a display. Such organic EL displays can be driven passively or actively, similar to LCDs, and, also as is the case with LCDS, active matrix displays are more preferable. More specifically, in active matrix displays, switching elements (typically two elements including a switching element and a driving element) are provided for each pixel and display of each pixel is controlled by controlling the switching elements, whereas in passive driving, a switching element is not provided for each pixel. Of these two types of displays, the active matrix is more preferable because much more precise displays can be achieved.
The organic EL element emits light when current flows through an organic emissive layer. In many cases, a hole transport layer and an electron transport layer formed of an organic material are provided adjacent to the organic emissive layer so as to assist light emission. These organic layers are apt to degrade when exposed to moisture.
Accordingly, in organic EL displays, in order to remove moisture from the organic layers, a cathode formed of a metal is provided for covering the upper portion of the organic EL element while a space above the display region (a region where pixels are provided) in which the organic EL element is disposed is made air proof and a drying agent is provided in this space.
However, there remains a demand for more reliable prevention of diffusion of moisture into the organic layers of the organic EL element. Although it is possible to increase the thickness of the cathode as a solution, for example, when the thickness is too large, the cathode would be deformed and peeled due to the resulting stress.