High-performance polymer light-emitting diodes utilizing modified Al cathode

We report an increase of electroluminescence (EL) efficiency by two orders of magnitude for poly(2-methoxy-5-($2^{\prime }$ -ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) based polymer light-emitting diodes (PLED) while employing Al as the cathode with an ultrathin layer of poly(ethylene oxide) (PEO). EL efficiencies of MEH-PPV PLEDs biased at 10 mA were found to be $0.017\mathrm{cd}∕\mathrm{A}$ at $31\mathrm{cd}∕{\mathrm{m}}^2$ , $1.50\mathrm{cd}∕\mathrm{A}$ at $2515\mathrm{cd}∕{\mathrm{m}}^2$ , and $4.96\mathrm{cd}∕\mathrm{A}$ at $8416\mathrm{cd}∕{\mathrm{m}}^2$ for applying Al, $\mathrm{PEO}∕\mathrm{Al}$ , and $\mathrm{PEO}∕\mathrm{LiF}∕\mathrm{Al}$ as the device cathodes, respectively. The significant improvement in the device performance is attributed to the promotion of minority carrier injection (electrons), where the threshold of the injection can be characterized through the deviation of Fowler–Nordhiem tunneling prediction.