We have measured the electrical characteristics and the efficiencies of single-layer organic light-emitting diodes based on poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV), with Au anodes and Ca, Al, and Au cathodes. We show that proper accounting of the built-in potential leads to a consistent description of the current-voltage data. For the case of Au and Al cathodes, the current under forward bias is dominated by holes injected from the anode and is space-charge limited with a field-dependent hole mobility. The Ca cathode is capable of injecting a space-charge-limited electron current.

• Received 24 August 1998

DOI:https://doi.org/10.1103/PhysRevB.58.R13411