High kinetic stability and high density of Ir(ppy)₃ doped organic semiconductor glasses

Glasses prepared by physical vapor deposition (PVD) can have advantageous material properties such as highly enhanced thermal stability and denser molecular packing, and thin glassy films prepared by PVD are utilized as the active layers in organic light emitting diodes (OLEDs). However, the stability and density of PVD glasses with compositions typical of OLED devices are not well studied. Here, we prepared Ir(ppy)₃ doped vapor-deposited glasses in 3 different organic semiconductor hosts; Ir(ppy)₃ in a dilute concentration is often used as a light emitter in phosphorescent OLEDs. We studied these glasses during temperature ramping using spectroscopic ellipsometry (SE) and found that the Ir(ppy)₃ doped PVD glasses have high kinetic stability and high density. Surprisingly, the observed kinetic stability exceeds that of single-component PVD glasses. This work allows further understanding of the material properties influencing OLED devices, thus facilitating the design of durable and stable devices.