Enhanced electron injection in polymer light-emitting diodes: polyhedral oligomeric silsesquioxanes as dilute additives
By blending monochlorocyclohexyl- polyhedral oligomeric silsesquioxanes (MCC-POSS) into poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1.4-phenylenevinylene (MEH-PPV), enhanced luminous efficiency (LE, cd A−1) and brightness were observed in polymer light-emitting diodes (PLEDs) using Al as the cathode. PLEDs made from MEH-PPV with 0.5 wt.% of MCC-POSS exhibit LE of 1 cd A−1, four times higher than that observed in simple MEH-PPV devices. x-ray diffraction studies, measurements of photovoltaic response and measurements of photoconductivity from the films of pure MEH-PPV and MEH-PPV with MCC-POSS demonstrated that the improved device performance results from mixing of MCC-POSS with MEH-PPV. The enhanced electron-injection into the emissive layer results from the effect of the ionic conductivity introduced by the addition of MCC-POSS.