Spin-cast thin semiconducting polymer interlayer for improving device efficiency of polymer light-emitting diodes

We report that adding a thin (similar to 10 nm) semiconducting polymer interlayer between apoly(styrenesulphonate)-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSS) hole transporter and an emissive semiconductor significantly improves the device efficiency of polymer light-emitting diodes (LEDs). With the interlayer, the external quantum efficiency (EQE) increases from 0.7%(0.4 cd/A at 3.7 V) to 1.9% (1.0 cd/A at 3.3 V) at 100 cd/m(2) for red LEDs and from 1.9%(6.2 cd/A at 3.4 V) to 3.0% (10.1 cd/A at 3.0 V) at 1000 cd/m(2) for green LEDs. An EQE of 4.0% is also observed in blue LEDs (35% increase). The interlayer is spin-coated directly on top of the PEDT:PSS layer from a poly(2,7-(9,9-di-n-octylfluorene)-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB) solution. This interlayer prevents significant quenching of radiative excitons at the PEDT:PSS interface by acting as an efficient exciton blocking layer. (c) 2005 American Institute of Physics.