Optical and Charge Transport Properties of Water/Alcohol-Soluble Quinacridone Derivatives for Application in Polymer Light Emitting Diodes

Sodium N,N′-bis(3-sulfonylpropyl)quinacridone (Na+QPSO3–), tetraphenylphosphonium N,N′-bis(3-sulfonylpropyl)quinacridone (Ph4P+QPSO3–), sodium N,N′-bis(6-sulfonylhexyl)quinacridone (Na+QHSO3–), and tetraphenylphosphonium N,N′-bis(6-sulfonylhexyl)quinacridone (Ph4P+QHSO3–) are employed as solution-processable electron injection layers (EILs) in multilayer polymer light emitting diodes utilizing poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) as the emissive layer. The electron mobilities of these oligoelectrolytes are comparable with conjugated polyelectrolytes, but the synthesis is much simpler. The choice of counterion can be used to tune electron mobilities and optical properties. Increased aggregation in solution positively influences device performance, yielding devices that outperform those that use a barium cathode with no barrier for electron injection. These oligoelectrolyte EILs were also tested in devices utilizing a blue emissive small molecule. The ease of synthesis of th...