Mesoscopic study of bipolar charge transport in polymer-based devices

We present generalised Monte-Carlo calculations of bipolar charge carrier transport in polydiacetylene (PDA) to assess effects of some key factors on the properties of polymer-based light-emitting diodes (PLEDs). Our mesoscopic model includes specific realisations of the polymer network and examines the effect of polymer structural order on current flow and charge recombination within the polymer layer. Specifically addressed are the issues concerning the fractions of polymer strands contributing to the charge injection processes at electrode interfaces and to electroluminescence (EL). Our results suggest that radiative recombination increases as short chain concentration increases, whereas current efficiency shows an opposite behaviour. Radiative recombination decreases as charge injection efficiency decreases and its internal efficiency seems to saturate for a luminescent chain concentration >30%. Our results also suggest that both current efficiency and space-charge increases as charge injection efficiency decreases. Polymer disorder due to inclusions in the network does seem to contribute to reduce both current and recombination efficiencies.