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BASF researchers are taming blue light

Laboratory with two persons dressed in blue

Having the blues is not always a bad thing, at least not for BASF’s researchers. In 1897, they produced the first ever artificial indigo-colored pigment. This dye, which had previously been an expensive luxury imported from India, was suddenly affordable, and can today be found in virtually every pair of jeans. The company now wants to create another innovation involving the color blue, but this time on the lighting market.

Only the right mixture of red, green, and blue light produces the white light of an organic light-emitting diode (OLED). But until now, manufacturers have had to make do with a blue dye that is relatively inefficient. The fluorescent emitters currently on the market convert no more than a quarter of the energy into light, with the rest being converted into heat. “What we want, however, are lamps and not hotplates,” says Dr. Karl Hahn who is in charge of BASF’s research in the field of organic electronics. BASF chemists therefore started looking for a solution to the ‘blue problem’ a few years ago. They discovered molecules that shine blue and are able to convert the energy almost entirely into light. These molecules belong to the highly efficient phosphorescent emitters used in OLEDs. There was just one snag, however: they only lasted a few minutes.

While long-lasting red and green variants of the highly efficient OLEDs are already available, there is still no corresponding blue in the palette. The reason for this is that blue light is particularly aggressive. “It is very short-waved and thus highly charged with energy. Blue light is therefore able to destroy molecular bonds like no other light can,” Hahn explains. The challenge for BASF researchers is to find molecules able to withstand this strong energy over a long period. An OLED must be long-lasting in order to be suited to applications such as lamps, cell phone displays, and TV sets. However, finding the right dye is not the end of the story. The other materials in the blue OLED sandwich must be robust in order to enable OLEDs to shine brightly and over a long period. BASF is therefore working on the entire materials system for blue diodes and aims to be the leading supplier worldwide for these active components.

BASF has already managed to extend the few minutes of life of its early molecules to several thousands of hours. “But lamp manufacturers want several tens of thousands of hours,” says Hahn. BASF’s researchers are working to achieve this goal in the company’s chemistry laboratories. Day after day, lab assistants are using vapor deposition techniques to coat small glass plates with dye molecules and materials that make them shine. Countless diodes have been produced in this way. “We constantly test new combinations,” says chemist Dr.-Ing. Soichi Watanabe, originally from Japan.

Watanabe is completely covered in protective clothing. “The wafer-thin layers on the diode must not, under any circumstances, be contaminated with dust particles,” he explains. Even a single speck of dust would act like a mountain on the much smaller molecular layers and destroy the lamps. Steam and oxygen are also poison to the organic molecules. They would quickly spoil. “It’s like with sushi. I would prefer to eat it fresh rather than a couple of days later,” says Watanabe. The lab assistants must immediately seal each individual glass plate with another glass plate once all the molecules are in place.

The finished diodes are tested in two chambers. In the first, trials are run on light intensity and other parameters. In the second, which looks like a small recording studio, the durability test is carried out. A large number of switchboards are attached to electrical cabinets and computers. On the black cabinets, 360 diodes shine for days on end. The series of figures on the screens show which lamps are worth continuing to work on. Watanabe and his colleagues continually assess these data.

In 2014, BASF hopes that the blue dye and the associated system components will be ready for the mass lighting market. By 2016, the BASF blue should have the necessary depth of color for the display industry. The researchers are aware that they will have to fight hard for every inch of progress until then. “We are working on a pioneering development, and every day this rekindles the team’s spirit of discovery,” says Hahn.

(Article: October 2012)

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