Dense co-deposited glasses of organic semiconductors have enhanced thermal stability

Physical Vapor Deposition (PVD) is utilized for production of organic semiconductor devices due to their favorable properties which cannot be accessible by other methods. Although layers in the device are usually composed of two or more components, the fundamental characteristics of co-vapor deposited glasses are elusive yet. Here, spectroscopic ellipsometry (SE) is employed to characterize optical properties, thermal stabilities and densities of co-deposited NPD&TPD glasses with varied compositions and deposition temperatures. We find that, regardless of the composition, highly stable glasses can be prepared. A strong correlation between thermal stability and density is observed, as expected from the surface equilibration mechanism. In addition, the transformation of the stable glass into the liquid occurs via a growth front that initiated at the free surface.