Formation of Ohmic Carrier Injection at Anode/Organic Interfaces and Carrier Transport Mechanisms of Organic Thin Films

摘要

We have shown that hole mobilities of a wide variety of organic thin films can be estimated using a steady-state space-charge-limited current (SCLC) technique due to formation of Ohmic hole injection by introducing a very thin hole-injection layer of molybdenum oxide (MoO_3) between an indium tin oxide anode layer and an organic hole-transport layer. Organic hole-transport materials used to estimate hole mobilities are 4,4',4"-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA), 4,4',4"-tris(N-2-naphthyl-/V-phenyl-amino)triphenylamine (2-TNATA), rabrene, N,N'-di(m-tolyl)-N,N'-diphenylbenzidine (TPD), and N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD). These materials are found to have electric-field-dependent hole mobilities. While field dependence parameters (β) estimated from SCLCs are almost similar to those estimated using a widely used time-of-flight (TOF) technique, zero field SCLC mobilities (μ_0) are about one order of magnitude lower than zero field TOF mobilities.