Trap-free, space-charge-limited currents in a polyfluorene copolymer using pretreated indium tin oxide as a hole injecting contact

We report time-of-flight, transient dark injection (DI) and current density versus voltage measurements on polyfluorene copolymer diode structures using pretreated indium tin oxide: (ITO) as a hole injecting contact. For ITO exposed to an oxygen plasma, coated in poly(ethylenedioxythiophene)/polystyrenesulphonic acid, or with both treatments, all measurements were entirely consistent with positive carrier, trap-free, space-charge-limited current theory. For untreated ITO, the behaviour is instead injection limited. (C) 2001 Elsevier Science B.V. All rights reserved.