New technology: Jiaotong University develops flexible white LED sheet light source

Light-emitting diodes (LEDs) have gradually developed into the mainstream technology of solid-state lighting and are widely used in lighting, display backlighting, automotive lighting industries, etc., and advanced flexible LED technology has also attracted more and more people to invest in research and development. According to the latest publication in the international optical journal "OpticsExpress", a research team from the National Chiao Tung University has developed a high-efficiency flexible white LED sheet, which is expected to be used in large-area lighting fixtures, wearable devices, displays and other fields in the future.

Usually when referring to flexible sheet light sources, the more well-known ones are organic light-emitting diodes (OLEDs). Lin Jianzhong, an associate professor at the Institute of Optoelectronic Systems of Jiaotong University, said that compared with OLED, flexible LED not only has higher efficiency and longer life, but also has lower cost and is very competitive.

The size of the flexible white LED published in "OpticsExpress" this time is about 5x5cm. It uses a polyimide (PI) flexible substrate and is covered with a layer of copper foil. The electrode pattern is produced through a photolithography process and oxygen plasma etching. The research team used flip-chip bonding technology to adhere 81 blue LED chips of 1.143x1.143mm size to the substrate with anisotropic conductive film.

In order to generate white light, a layer of polydimethylsiloxane (PDMS) phosphor film needs to be added to the LED chip, containing yellow phosphor "Y3Al5O12: Ce3+" and red phosphor "CaAlSiN3: Eu2+". PDMS is non-toxic and non-flammable, and has the characteristics of high transmittance, high stability and high flexibility.

Flexible white LED sheet structure

Using flip-chip LED, PI substrate and PDMS phosphor film, a flexible white LED sheet with a thickness of about 6mm has been successfully created, which can emit warm white or cool white light. At color temperatures of 3,000K and 5,000K, the maximum luminous efficiency can reach 81lm/W and 120lm/W respectively. Not only is the luminous efficiency high, the light source distribution generated is also uniform, with a uniformity of 85%. As for the degree of flexibility, the radius of curvature can reach 15mm.

The luminous flux performance is not greatly affected by deflection changes, and is suitable for flexible displays and lighting fixtures

In addition, the flexible white light LED was tested for 1,000 hours of service life at an indoor temperature of 25 degrees Celsius. The actual measurement result was that the luminous efficiency lost 2.5%, and it is estimated that it will lose 22% after 10,000 hours. Although the service life is not as long as that of ordinary LED lighting, with the continuous improvement of the overall performance of flexible white LED, it is expected to further make breakthroughs in technology and actually introduce it into more applications in the future

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