Iridium has been generating light and color for organic LED (OLED) screens on smartphones and TVs, but it is the rarest metal on Earth; USC Dornsife scientists find a surprising, cheaper solution: Copper is the answer, according to their study, published Feb. 8 in the journal Science.

The current technology that is in every Samsung Galaxy phone, high-end Apple iPhone and LG TV relies on iridium compounds for the colors and light on OLED screens,” says Mark E. Thompson, a chemist at USC Dornsife College of Letters, Arts and Sciences and the Ray. R. Irani Chairman of the Occidental Petroleum Corporation Chair in Chemistry.

Iridium’s link to dinosaurs

Copper definitely solves the problem of availability since it is a plentiful metal worldwide. Iridium, on the other hand, is found in only a few places — mostly South Africa and parts of Asia.

The most widely-accepted hypothesis that explains iridium’s scarcity and its origins is that it traveled here on a meteor — the same one that wiped out the dinosaurs 65 million years ago.

Unless another meteor like that hits Earth, iridium will continue to dwindle in supply. Demand for it is only increasing as smartphones, TVs and other devices that feature OLED screens gain popularity. OLEDs have come to replace LED LCD screens. In an OLED screen, each pixel generates light, while in the LCD screens, pixels are illuminated by an LED backlight.

Blue chemistry

Besides its scarcity, iridium has another drawback for OLED technology that has perplexed chemists for more than two decades: weaker molecules for generating blue light.

When the molecules from the iridium compounds are excited, they generate two of the OLED screen’s primary colors — red and green — very efficiently, quickly and in devices that give very long operational lifetimes, says Thompson, whose lab engineered the iridium-based red and green molecules.

The third requisite color, blue, has been the bane of OLED technology because blue emissive OLEDs have a short lifetime. Thompson explained that the bonds within the blue molecules tend to break down. Blue molecules also require more electricity than the green and red molecules to energize them. Since blue is among the primary colors for OLED, its poor performance can affect a range of colors that you see on a screen that contain any blue.

Thompson’s team may have solved that, too, with their new copper complex — a more rigid molecular complex than the prior, failed types of copper compounds, which were weaker. The new compound’s rate of light emission also matches iridium’s, so the energy is converted efficiently into light and color, the chemists found.

 

 

(Releaed by: USC Dornsife)