Abstract The interface between Al and tris-(8-hydroquinoline) aluminum (Alq 3) was studied using in situ medium energy ion scattering spectroscopy. We compared two interfaces of Al/LiF/Alq 3 and Al/Alq 3 with the elemental depth profile of each interface. The thin LiF changes the interfacial structures significantly; the excess Li in the LiF layer diffuses into Alq 3 while F does not. In addition, the Al diffusion into the Alq 3 layer during the initial stages of Al deposition is reduced significantly compared to the interface without the LiF interlayer. The LiF interlayer makes a more abrupt metal–organic interface, which would contribute to the efficiency and stability of the organic light-emitting device.