Flexible OLED

One of the attractive advantages of OLED is the possibility of depositing organic films on flexible substrates. The use of thin flexible substrates will significantly reduce the weight of flat panel displays and provide the ability to conform, bend or roll a display into shapes. Moreover, it will open the possibility of fabricating displays by continuous roll processing, thus providing the basis for low-cost mass production. To date, some FOLEDs have been fabricated on flexible plastic substrates, but their performance is far from the requirement of display applications. Several problems must be solved before FOLEDs can become a reality. The extreme sensitivity of OLEDs to water and oxygen requires an extremely low gas permeability of the substrates that is far from what any known transparent polymeric substrate can achieve. Unlike OLED on rigid glass, the encapsulation for flexible OLED is neither rigid metal sheet or glass caps. Therefore, an advanced thin film encapsulation technique has to be developed. It generally consists of single layer or multi-layers of nano-scale organic and inorganic thin films, which act as a barrier to protect the electrode and active region from water and oxygen permeation. 

CityU's Flexible OLED Shown in the Program of "Technofrontier" (Feb 2006) Produced by Radio Television Hong Kong (RTHK)

The CityU’s OLED research team started the work in flexible OLED in 2001. The university also participated in an ITF project (2001) and 863 program (2003) to work on flexible OLED. In the ITF project, we succeeded in demonstrating a monochrome 7-segment flexible OLED, with a power efficiency and current efficiency of 1.5 lm/W and 4.1 cd/A, respectively. The device can be bended to 180° without notable structural and functional failure. In the 863 project, we succeeded in fabricating a monochrome 128x64 dot-matrix flexible OLED on PET substrate with a luminance and current efficiency of 150 cd/m² and 1.0 cd/A, respectively, at a driving voltage of 9 V. The pixel size of the device is 0.2 mm x 0.2 mm in which no pillar separator was constructed on the substrate. We also demonstrated another top-emitting flexible OLED on a steel foil. The turn-on voltage (at 1 cd/m²) of such a FOLED was 3 V, and the light-emitting efficiency reached 0.56 cd/A. The FOLED was shown to bend substantially without incurring detectable degradation. Using different materials and/or device structures, CityU team has done some unique work and acquired proprietary expertise in the area of flexible OLEDs in reference to other teams reported above.