PMOLED is a kind of organic electroluminescent diode, its full name is Passive Matrix Organic Light-Emitting Diode, that is, passive matrix organic light-emitting diode. Compared with other types of OLEDs, PMOLED has the advantages of low power consumption, high contrast ratio, fast response and small pixel size, so it is suitable for small-size display applications, such as mobile phones, watches, MP3 and other electronic products.

The structure of PMOLED usually consists of four different layers, these layers include the bottom plate (Substrate) layer, the light emitting layer (Emissive) layer, the cathode and anode (Anode/Cathode) layer and the encapsulation (Encapsulation) layer. Below we will introduce the function and structure of each layer separately.

1. Bottom plate layer: The bottom plate layer is the lowest part of the PMOLED display, mainly made of metal or non-metallic materials (such as glass or plastic), and its main responsibility is to provide support, pressure balance and conductivity functions.

2. Light-emitting layer: The light-emitting layer is the key part of PMOLED, which is composed of a layer of organic material film with light-emitting function. These organic materials can be selected to emit in different colors, such as blue, green or red, enabling full-color displays. By applying an electric field, the organic material will undergo electroluminescence, so the light-emitting layer of the PMOLED is also called the Emissive layer.

3. Cathode and anode layers: The cathode and anode layers are another important part of PMOLED. Depending on the structure, it can be divided into two parts: cathode and anode. Cathodes are usually made of materials such as aluminum and calcium, while anodes are usually made of materials such as copper and silver. When current passes through the cathode and anode, the light-emitting layer of the organic material will be excited to emit light.

4. Encapsulation layer: The encapsulation layer of PMOLED is the outermost layer of the display, which is used to protect the internal structure from air and moisture, and provide proper thermal management and mechanical protection. It is usually made of hard materials such as polymethyl methacrylate (PMMA) or glass.

The working principle of PMOLED is based on the phenomenon of electroluminescence. When an electric current is passed through the cathode and anode, the light-emitting layer of the organic material emits light, a phenomenon commonly known as self-luminescence. Each pixel consists of a bottom plate, a cathode, a light emitting layer and an anode. In the pixel structure of PMOLED, each pixel only needs one ground wire and one control wire, which greatly simplifies the debugging and control of the pixel. By allowing electrons to travel between the cathode and anode, the brightness and color of the pixel can be controlled.

In summary, Passive Matrix Organic Light-Emitting Diode (PMOLED) is an organic electroluminescent diode whose structure includes a bottom plate, a light-emitting layer, anode and cathode layers, and an encapsulation layer. The working principle of PMOLED is based on the phenomenon of electroluminescence. By controlling the current between the cathode and the anode, the brightness and color control of the pixel can be realized.