Formation of MoO₃/Organic Interfaces

Abstract Molybdenum trioxide (MoO₃) has been extensively used in numerous organic semiconductor devices for hole injection and extraction. In this paper, photoelectron spectroscopy combined with cleavage and sputter depth profile has been used to probe the structures of buried MoO₃/organic semiconductor interfaces. Organics used in this work include: tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA), N,N′‐bis(naphthalene‐l‐yl)‐N,N′‐bis(phenyl)benzidine (NPB), 4,4′‐bis(carbazol‐9‐yl)‐2,2′‐biphenyl (CBP), and 1,3‐bis(N‐carbazolyl) benzene (mCP). It is found that there are two distinct types of interfaces: sharp interfaces (type‐I) where the oxide layer has limited or no diffusion when deposited on organics that have a high glass transition temperature such as TCTA and NPB; mixed interfaces (type‐II) where the formation of interfaces is followed by significant diffusion and reaction on organics having low glass transition temperatures such as CBP and mCP. The causes for these two types of interfaces are discussed.