New prospects for OLED lighting automotive and wearable applications

Organic LEDs (OLEDs) are now commonly used in TV and cell phone screens, but they are expected to be the next big thing in solid-state lighting (SSL) technology, and may be suitable for many other applications. In terms of many applications, inorganic LEDs are still more economical and technically meaningful, but OLEDs have some interesting features that are lacking in inorganic LEDs. Together with new production technologies, it is expected to reduce the manufacturing cost of OLEDs. More cost competitive.

The OLED emits light by applying a current to an electroluminescent layer made of an organic small molecule or a polymer, and can be fabricated into a rigid or soft sheet. OLEDs are well suited for applications that require a uniform distribution of light, such as digital displays for screens and smartphones. The following figure shows a typical OLED structure - in addition to the electron and hole (hole) transport layers, there are also luminescent layers for emitting red, green and blue light.

When a voltage is applied such that the anode is positive with respect to the cathode, electrons flow through the OLED. The electrostatic force in the OLED causes electrons and holes to oppose each other and emit light when each electron is combined with a hole.

The efficiency of OLEDs lags significantly behind inorganic LEDs, and the luminous efficiency of mass production is about 60-90 lumens per watt (lm/W). The luminous efficiency of various commercial LED bulbs ranges from about 100 lm/W to over 200 lm/W. As in the case of inorganic LEDs, there is a trade-off between light efficiency and color rendering. Therefore, whether in current operation (similar to inorganic LEDs) or during storage (the culprit is oxygen and moisture infiltration), lumen loss of the OLED may result.

OLEDs are widely used in the display market to replace liquid crystal displays (LCDs). Although LCD displays have been around for more than 20 years, OLED commercials have been around for only five years. Both are flat display technologies and use a pixel matrix that is addressed through the backplane. In addition, red, blue, and green light sources are included in each of the two technologies, and can be manufactured in a variety of sizes. However, there are also important differences between the two.

Although OLEDs require more complex circuit structures, LCDs require more optical layers. LCD displays require backlighting, while OLED displays do not. Moreover, as described above, OLEDs are more advantageous when they are produced using a flexible substrate. Therefore, OLED is gradually becoming the preferred display technology.

The power consumption is a bit complicated. Although the power consumption of an LCD display depends on the backlight, the power consumption of the OLED display depends on the content of the screen; therefore, the OLED is not necessarily more advantageous than the LCD in this respect.

According to DSCC forecasts, by 2022, OLED will replace the LCD technology used in smartphones, mainly due to the advanced form factor of OLED technology, including foldable displays using OLEDs.

In addition to display applications, the European Union's (EU)-supported Horizon 2020 research has recently demonstrated innovations that will reduce manufacturing costs of OLEDs by 90%, making them cost equivalent to inorganic LED lighting products. These innovations include the use of planarized mild steel as a production substrate, transparent top contacts, and thin film packaging, making OLED production no longer dependent on glass substrates and packages. Although the industry has not yet seen products using this new production technology, its potential applications include general lighting, automotive lighting, and wearable devices.

Recently, under the industrial cooperation hosted by the European Lyteus project - the goal is to promote the commercialization of OLED technology, the Holst Centre in the Netherlands and the Fraunhofer FEP in Germany. The method has achieved innovation and is able to achieve what it claims to be “the longest OLED product in the world” (15 meters). This achievement demonstrates the “tailor-made” OLED custom lighting that makes it suitable for a wide range of applications, from transportation to interior design. But the main drawback of this technology is the luminous efficiency, which is only about 15 lm/W - which is really too low for OLED technology.

Finally, for general lighting, US supermarket chain Wegmans Food Markets announced last year that it would install OLEDs/LEDs in specific stores and hanging fixtures at its headquarters (Rochester, NY) in order to provide customers and employees with the best quality lighting. Lighting combination. The OLED components of such hybrid luminaires will be manufactured by OLED luminaire manufacturer OLEDWorks.

OLED-based lighting applications have been widely used in display products and are now entering other lighting markets. However, production costs and luminous efficiency are still the main obstacles to their wider adoption. As the relevant research continues, it is expected that these limitations will eventually be overcome. We look forward to seeing OLED lighting products in life soon.