Using transistor technique to study the effects of transition metal oxide dopants on organic charge transporters

Organic thin-film transistor (OTFT) technique was used to investigate the effects of doping on N’-diphenyl-N,N’-bis(1-naphthyl)(1,1’-biphenyl)-4,4’diamine (NPB). Different transition metal oxides (TMOs) including molybdenum oxide (MoO3), vanadium oxide (V2O5), tungsten oxide (WO3) were employed as dopants. Using temperature dependent OTFT measurement, the carrier mobility and carrier concentration of the doping system can be extracted simultaneously. Generally, all TMOs form p-dopants and the conductivities increase drastically after doping. Among the TMOs, MoO3 appears to be the most effective p-type dopant. It generates the largest free carrier concentration (1.4 × 1017 cm−3) and has the least activation energy (∼138 meV) for modest doping concentration of ∼5 vol.%. Detailed carrier transport analysis indicates that the carrier mobilities were slightly reduced. It appears that the increase of free carrier concentration is the deciding factor in the conductivity enhancement in TMO-doped NPB.

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► Effects of doping transition metal oxides into organic hole transporter was examined by organic thin film transistor technique.
► The conductivity was improved after doped with TMOs.
► The improved conductivity was realized by the increased free carrier concentration after doping.
► MoO3 was found to be the best p-dopant among three TMOs candidates (MoO3, WO3 and V2O5).