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 (MoO(3)), vanadium oxide (V(2)O(5)), tungsten oxide (WO(3)) 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, MoO(3) appears to be the most effective p-type dopant. It generates the largest free carrier concentration (1.4 x 10(17) cm (3)) and has the least activation energy (similar to 138 meV) for modest doping concentration of similar to 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. (C) 2011 Elsevier B.V. All rights reserved.