Transport mechanism and electrical properties of LECs based on mLPPP active material

The paper discusses the carrier transport mechanism and the electrical characteristics of light-emitting electrochemical cells (LECs) based on a methyl substituted laddertype poly(para phenylene) (m-LPPP). An intensive set of measurements, such as Current-Voltage (I-V), Capacitance- Voltage (C-V) and temperature investigations are used to track the formation of the highly conductive contacts, the initial diffusive carrier transport regime, the onset of a net voltage drop across the polymeric bulk and the final resistive behavior of the device in which carriers are driven by drift. In particular, the strong increase of the capacitance is shown to be a signature of the large carrier injection through the contacts and their diffusion through the active layer. Clearly visible hysterisis behavior in the I-V and C-V plots are also discussed to suggest polymer electrochemical doping at the interfaces.