Enhanced quantum efficiency in polymer electroluminescence devices by inserting an ultrathin PMMA layer

We report an increase of electroluminescence (EL) efficiency by about two times for poly(2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) based polymer light-emitting diodes (PLED) while employing an ultrathin layer of poly(methyl methacrylate) (PMMA) between a hole injection layer, polyethylenedioxythiophenne:polystyrenesulfonate (PEDOT:PSS) and an emitting layer, MEH-PPV. The peak power efficiency of the control device (ITO/MEH-PPV/LiF/Al) was 0.42 lm/W with a current efficiency of 0.66 cd/A. The device with the optimized thickness of PMMA interface layer shows the highest power efficiency of 1.15 lm/W at a current efficiency exceeding 1.83 cd/A. The significant improvement in the device performance is attributed to the decrease of holes injection and the promotion of electrons injection, which cause the balance of the carriers within the emitting layer.