Improved polymer light-emitting diodes by the tuning of charge balance

We have prepared polymer-small molecule hybrid electroluminescence devices with improved brightness and efficiency by a doping method. The doping effect on the hole transporter N,N′-diphenyl-N,N′-bis(4′-[N,N-bis(naphth-1-yl)-amino]-biphenyl-4-yl)-benzidine has been investigated in bilayer devices with structure of ITO/MEH-PPV: TPTE/PBD/Al. It was found that the effective hole mobility increases with increasing TPTE content in the blend, which is directly determined by space charge limited current at high voltage. The brightness and EL efficiencies of the doped OLEDs were increased significantly over those obtained for devices based only on MEH-PPV, which is attributed to more balanced electron and hole recombination due to improved hole mobility.