Novaled and Colnatec hope to control film thickness with novel sensing technology on OLED roll-to-roll production lines, while researchers at the University of Utah have tuned a plastic polymer that could yield true white OLEDs.
While OLEDs cost more than LEDs and trail in efficacy, researchers and commercial companies continue to pursue OLED technology for solid-state lighting (SSL) applications because of the inherent diffuse, surface-emission lighting properties. OLED manufacturer Novaled hopes to reduce manufacturing cost by using temperature-controlled sensors developed by Colnatec to accurately control the thickness of films. Meanwhile, at the University of Utah, researchers have been able to generate true white light from a polymer that could enable cheaper white OLEDs within two years.
Continuously-run OLED production
One production angle that promises to cut the cost of OLED manufacturing is roll-to-roll, or continuously-run production lines. Today, most OLED panels for SSL applications are made one small panel at a time. A continuous system deposits the films and organic materials as a continuous sheet of flexible substrate moves from a supply roll, passes through the production line, and is captured on a take-up roll.
One challenge of continuous processing is accurate control of deposition layers that can be on the order of nanometers in thickness. Accurate measurement is also dependent on the temperature of the sensor used for the measurement and the substrate material.
Colnatec has developed a technique to heat the sensor with accurate control to a known temperature that also reduces stress and relaxes the film on the production line. The partners will now test the heated quartz crystal microbalance (QCM) sensor system that Colnatec calls Tempe.
"Our film thickness monitoring system, Tempe, was developed to stabilize OLED device performances, for its material characterization capabilities, and for in-situ, self-regeneration properties," said Scott Grimshaw, CTO and co-founder of Colnatec. "At the same time, Tempe has the potential to increase runtime, decrease downtime, and significantly reduce overall costs. We are confident of outstanding results of our system in the continuous OLED production at Novaled."
"OLEDs absolutely need accurate layer sizes, since without temperature compensation, the device performance is directly affected," said Kai Gilge, head of Novaled's engineering division. "After positive pre-tests we are now about to implement Tempe in our continuously-run OLED production. The new sensor system of Colnatec will help to speed up our development time for OLED prime materials for our OLED display and lighting customers."
White OLED emission
While the Novaled work could pay dividends in the coming months, the work at the University of Utah is much further from commercial deployment. But university research could solve a fundamental challenge that pervades all of SSL technology: direct production of white light.
LEDs either mix emitter colors to produce white light or rely on phosphor. Likewise, OLEDs generally mix red, green, and blue (RGB) pixels to create white light. The implementation can mean additional layers in an OLED manufacturing process.
The Utah team was able to develop a single plastic-like polymer that can emit the needed RGB light. The team, led by University of Utah physicist Z. Valy Vardeny, inserted platinum metal atoms at varying intervals along the polymer to tune the color emitted along the polymer. Presumably, such a polymer could produce white light from the multiple colors.
Vardeny stressed that the team had not built such an OLED yet. The lab results used light to stimulate the colors on the polymer. An OLED would require electrical stimulation. But Vardeny believes that the work could lead to white OLEDs within two years.
"This polymer emits light in the blue and red spectral range, and can be tuned to cover the whole visible spectrum," said Vardeny. "As such, it can serve as the active layer in white OLEDs that are predicted to replace regular light bulbs."
The Utah research was in part funded by one of the US Department of Energy (DOE) research grants. The university worked with the DOE's Los Alamos National Laboratory on the project. Additional funding came from the National Science Foundation, the National Natural Science Foundation of China, and China's Fundamental Research Funds for the Central Universities.
About the Author Maury Wright is Editor of LEDs Magazine and Illumination in Focus.
