Phosphorescent Organic Light-emitting Devices to Sense Contact Stresses

Abstract

ABSTRACTWe studied the electrical and optical responses of organic light-emitting devices (OLEDs) with green and red phosphorescent dyes doped in a polymer matrix to compressive stresses. The green OLED converted stresses as low as 6.8 kPa into measurable and reversible changes in both current density and electroluminescence (EL) intensity. The current showed a nearly linear characteristic response with sensitivity up to 205 μA kPa-1, whereas the EL intensity decreased by over three orders of magnitude at 107 kPa. In contrast, stress-induced modulations in current and light intensity were noticeable in the red OLED only above 160 kPa. The discrepancy has been attributed to different rates of stress-enhanced back exciton energy transfer between guest and host molecules, which quenches the EL of the green OLED, but has a much smaller impact on the performance of the red OLED. It is expected that similar green phosphorescent OLEDs built on large curved surfaces may directly image stress distributions and sense touch on a par with a human finger.