Iridium (III) device emits red light efficiently

Flexible displays have proven inefficient compared to other types of displays and, so far, expensive to fabricate. A new solution processing technique holds promise for fabricating high-efficiency vacuum-deposited small-molecule organic light-emitting diodes (OLEDs) at low cost. Researchers at the Samsung Advanced Institute of Technology (Gyeonggi-do, Korea) and Sookmyung Women’s University (Seoul, Korea) used a zwitterionic cyclometalated iridium (III) complex structure, (pic)₂Ir⁺[BP(O^-)(OH)]-a unique red phosphorescent material that is soluble in organic solvents-to achieve a luminous efficiency of 12.62 cd/A with fast response time. Using (pic)₂Ir⁺[BP(O^-)(OH)] as a dopant in a polymeric host of poly (N-vinyl carbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD), the group achieved ultraviolet and visible emission spectra at 360 nm, between 380 to 450 nm, at 492 nm, and with peak emission at 606 nm. Unlike previous devices, this one did not undergo a drastic change of luminous efficiency at high current densities. In the near future, devices using this material may be fabricated and applied to standard flat-panel OLED displays and solid-state lighting. Eventually, says lead researcher Tae-Woo Lee, solution-processing of low-cost, flexible flat-panels OLED displays may be realized. Contact Tae-Woo Lee at [email protected].