Charge transport study in bis{2-(2-hydroxyphenyl) benzoxazolate} zinc [Zn(hpb)2]

The nature of the electrical transport mechanism for carrier transport in pure bis {2-(2-hydroxyphenyl) benzoxazolate} zinc [Zn(hpb)2] has been studied by current-voltage measurements of samples at different thicknesses and at different temperatures. Hole-only devices show ohmic conduction at low voltages and space charge conduction at high voltages. The space charge conduction is clearly identifiable with a square law dependence of current on voltage as well as the scaling of current inversely with the cube of thickness. With a further increase in voltage, the current increases with a Vm dependence with m varying with temperature typical of trap limited conduction with an exponential distribution of trap states. From the square law region the effective charge carrier mobility of holes has been evaluated as 2.5 x 10-11 m2 V-1 s-1. Electron-only devices however show electrode limited conduction, which was found to obey the Scott-Malliaras model of charge injection.