Use of ionomer as an electron injecting and hole blocking material for polymer light-emitting diode

Abstract

Light-emitting diodes of $\mathrm{poly[2-methoxy-5-(}{2}^{\prime }\mathrm{-ethyl-hexyloxy)-1,4-phenylene\; vinylene}$ ] (MEHPPV) are fabricated using sodium sulfonated polystyrene (SSPS) ionomer containing 10 mol % ionic groups as an electron injecting and hole blocking material. When an electric field stronger than ${\text{2.7×10}}^7\hspace{0.17em}\mathrm{V/m}$ is applied, SSPS in the indium–tin oxide ITO/MEH-PPV/SSPS/Al system causes a bridging effect between sodium ions and the Al cathode at the SSPS/Al interface, leading to excellent electron injection. Furthermore, the ionomer has a high band gap energy of $\text{∼5\hspace{0.17em}}\mathrm{eV},$ resulting in hole blocking. The operating voltage for the ITO/MEH-PPV/SSPS/Al is reduced by $\text{∼60\%}$ and the relative quantum efficiency is enhanced by three orders of magnitude compared with those of the corresponding single-layer MEH-PPV device.