Important Progress in White OLED with Adjustable Color Temperature Made by Prof. Zhang Zhaoyu's Group

After two years’ day and night, a significant progress has been achieved in the area of single emissive layer white organic light-emitting diode devices with adjustable color temperature by Prof. Zhaoyu Zhang’s group in School of Science and Engineering at CUHK-Shenzhen. His group has developed a single organic molecule, tris(4-(phenylethynyl)phenyl)amine (TPEPA), with temperature-sensitive photoluminescence. 
 

By applying this molecule as the only emissive layer which is provided by Prof. Hsing-linWang’s group from Southern University of Science and Technology, a simplified white OLED device with a 3.5% EQE has been successfully fabricated. The goal  is to let people have the feeling of natural lighting indoors. This work has been published in peer-reviewed journal, Advanced Materials (IF=21.9), entitled “Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light-Emitting Diodes Based on a Single Emissive Layer.”

Figure 1. OLED light source with different color temperature can achieve different daylight illumination effects. Our goal is to let people have the feeling of natural lighting indoors.

In recent years, full-color OLED technology has been widely used in flat panel display. White light OLED technology is also expected to become the next generation of solid-state lighting source due to its advantages of human eye friendliness, low energy consumption, large-area fabrication, and tunability of its color temperature. Our goal is to allow people to have a real lighting experience in the natural world. However, white OLEDs still have the disadvantages of high preparation cost and complicated preparation process, which largely limit the commercialization of white OLED technology. With the increasing demand of people's life quality, a single color temperature light source can not meet people's living needs. To meet the psychological and physiological needs in different light environments and high optical indicators for specific lighting occasions, the light source is required to adjust the brightness as well as change the color temperature to achieve different lighting conditions which will improve the display index of the illumination source.
 

This new type of single emissive layer white OLED device. The device utilizes a novel temperature-sensitive organic fluorescent small-molecule  material with adjustable emission peaks in the temperature range from room temperature to 300℃. By controlling the substrate heating temperature and time precisely, a full-spectrum luminescence based on a single material is obtained (Fig. 2). The external quantum efficiency of the white light-emitting device reaches 3.4%, and the maximum brightness reaches 2000 cd/m2, which is the highest efficiency achieved by the single emitting layer white OLED device and is an important breakthrough in the field of organic photovoltaic materials. Compared with the prior works, this novel route greatly saves material cost and manufacturing process cost. In addition, it will provide new ideas and strategies for the commercialization of white light OLED panel.  

Figure 2. OLED device with organic small molecule TPEPA as emissive layer that produces light covering nearly whole visible spectra controlled by different temperatures.

Article link: https://doi.org/10.1002/adma.201900613

Profile of  Prof. Zhaoyu Zhang

Education Background：

PhD of Caltech 

MS and BS of University of Science and Technology of China

Research Field：

Organic Light Emitting Devices; Thin Film Solar Cells; Nanolasers; Perovskite optoelectronics