Polymer White-Light-Emitting Diodes with High Work Function Cathode Based on a Novel Phosphorescent Chelating Copolymer

Polymer white-light-emitting diodes are fabricated based on the blend of poly[9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl]-end capped with polysilsesquioxane (PFO) and a chelating copolymer ofpoly[(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene-alt-2,7-(9,9-dioctylfluorene))-co- [2,7-(9,9-dioctlyfluorene)-alt-5,5-bis(2-(4-methyl-1-naphtha-lene) pyridine-C 2 ,N) iridium (III) acethylacetonate]] (PFN-NaIr). The device with the sole aluminium cathode is able to produce a comparably white electroluminescence efficiency of 1.31 cd/A to that of the device using low work function cathodes (such as Ba, Ca, etc.). The CIE coordinates of the white light emission consisting of red, green and blue three components are nearly at (0.34, 0.35). The mechanism of the white light emission from the device with the Al cathode is investigated, which is related to the efficient injection of electrons through the interface of PFN-NaIr/Al.