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Materials Science Professor Unveils Friendlier OLED Lighting

OLED's blanketing light is better for households than LED's spot pattern

2013/03/08 | By Ken Liu

Preliminary results of an ambitious OLED project led by materials scientist Prof. Jwo-huei Jou of the National Tsing-Hua University of Taiwan has been achieved: A small organic light emitting diode (OLED) panel emitting much friendlier correlated color temperature (CCT) than candle's 1,914 Kelvin with color rendering index (CRI) of 93, narrowly lagging the benchmark of 100 for a candle.

Jou compares his candlelight-like OLED (in right hand) with candle light. (Photo courtesy of Prof. Jou)
Jou compares his candlelight-like OLED (in right hand) with candle light. (Photo courtesy of Prof. Jou)

A U.S.-trained Ph.D., Jou is working to develop advanced OLED-lighting technologies with friendly features that do not exist in any available lamps in cooperation with the government-backed Industrial Technology Research Institute (ITRI) and several private organizations with funding from the Ministry of Economic Affairs (MOEA).

The OLED project team has three objectives: develop a lighting technology with dusk-to-dawn wavelengths as natural light, extraordinarily high CRI and low Kelvin.

Higher CRI means colors of objects look more natural under a light relative to those under sunlight.

The team introduced the natural-light-simulating wavelength technology around two years ago and the other two in January this year.

The natural light wavelengths are achieved by varying the voltage through the OLED panel from three to nine volts. “Truly there is genius in simplicity as this plain driver-IC can automatically modulate the voltage to render any desired color temperature between 2,200 and 8,000 K anytime,” says Jou, who is also credited with reportedly introducing the world's first OLED rated at 51 lumen-per-watt in 2002.

High CRI
The extraordinarily high CRI and the extraordinarily low K, Jou stresses, are two killer applications that the team has developed for OLED lighting. “OLED's CRI can be sorted into four grades: low (below 40), middle (between 40 and 75), high (between 75 and 90) and ultra high (above 90). Most European and Japanese OLED manufacturers have to discount product prices as they can't introduce ultra-high OLEDs,” he comments.

Jou estimates the revenue worldwide from ultra-high CRI applications equals the other three applications combined. “Product differentiation can't be achieved in the OLED market without developing high CRI lighting,” he stresses, adding that the team aims to improve the index towards the optimal 100.

Lighting color temperature, Jou notes, is closely related to human health, which is enhanced with lower K lighting. “Medical findings show that high Kelvin lighting is carcinogenic than low K lighting: higher K or whiter light impedes melatonin activity in human body quicker than low K light. So, people who work night shifts and are exposed to whiter light as nurses, telephone operators and fight attendants have higher risk of cancers. Candle light is 1,914K and five times lower than fluorescent light's 6,000K at the same lux. Our low K technology delivers as low as 1,400K,” he reports.

The candle-like OLED, Jou says, has 200 higher efficacy than candlelight. However, he concedes, producing low K and high CRI at once is not without hurdles. “The hardest is achieving seamlessly wavelengths similar to sunlight's,” Jou stresses.

Manufacturing cost is another challenge Jou's team is working to improve so that makers can eventually commercialize the OLED technologies. “Current manufacturing processes, whether spot or linear vacuum evaporation method, are material intensive, delivering only 5% to 20% of organic materials to desired areas of a substrate,” the professor says.

Area Type
Jou's team is developing a method which he calls “area type”, another “killer application,” for OLED lighting manufacturing. “In the laboratory, we've achieved 75% success rate,” he reports.

Illumination effects of candlelight (left) and the candlelight-like OLED (Photo courtesy of Prof. Jou)
Illumination effects of candlelight (left) and the candlelight-like OLED (Photo courtesy of Prof. Jou)
The concept of the unique method is quite simple: Blend materials and spread mixture on substrate with undisclosed approach and put it into vacuum evaporation chamber. But how many substances to mix and how to assure evenness of the spread? “That's our secret recipe which we'll apply for patents,” Jou says.

Usually, OLED manufacturers using spot or linear evaporation approach require red, green and blue organic luminous substances as well as one high-energy chemical element as agent for amplifying the intensity, according to Jou. “Ultra high CRI demands more chemical elements,” he notes.

The professor points out that OLED manufacturing equipment accounts for around 40% of manufacturing cost, materials 30% and OLED substances 15%. His team will introduce the “area type” manufacturing equipment in two years. “It is an integrated production equipment capable of finishing the products at application stage. LED production lines can not achieve this because the production is divided into several stages from epitaxy process and die slicing to packaging and assembly on dedicated machines. So, our process will bring down OLED production cost to below LED's,” Jou analyzes.

Jou's optimism about OLED over LED is due to not just cost but inherent advantages. “LED is a spot light source that tends to glare; while OLED light blankets comfortably, which is more suitable for households,” he stresses.

The team has mastered at least 10 crucial technologies for OLED in the government-funded project and applied for patents, some still pending. The paper on the candlelight-like technology has been published in the journals Advanced Functional Materials and MaterialsView. Jou's laboratory at the university has won at least 40 patents on OLEDs and been approached by several suppliers at home and abroad over patent licensing deals.

Upbeat about the market outlook for OLED, Jou estimates the new light source to snatch up a good share of the lighting market and flat-panel display market. Worldwide, the lighting market is projected to generate revenue of US$113 billion by the end of this year, with the display market forecast to achieve the same by 2018, he estimates.