Highly Efficient Near-Infrared OLED Created

Michael A. Greenwood

By using a different type of doping agent, researchers have significantly enhanced the efficiency of organic LEDs (OLEDs) that emit in the NIR region. Diodes with such capabilities have applications for night-vision displays and sensors.

An 11-member research team led by Mark E. Thompson, a professor in the department of chemistry at the University of Southern California, Los Angeles, found that, when a phosphorescent platinum porphyrin complex was used as a doping agent, the performance of the OLED improved noticeably.

Previously, the emission layers of OLEDS were doped with fluorescent dyes. The researchers replaced this with a phosphorescent Pt-metalloporphyrin dopant that harvests both the singlet and triplet excitons formed in electroluminescence. Wavelengths ranged from the NIR into the red, with peak emission from 380 to 650 nm. The investigators said that most research with OLEDs to date has focused on devices that emit in the visible range of the spectrum.

Test results showed that the device maintained >90 percent of its efficiency after 1000 hours of operation. They also showed that temperature variations affect the operating voltage. The researchers said that further study is necessary to determine the lifetime of the device at radiances suitable for night-vision goggles. Longer wavelength emissions also are possible if the conjugation length of the ligand is extended.

Angewandte Chemie International Edition, Feb. 5, 2007, pp. 1109-1112.