Improved efficiencies of light-emitting diodes through incorporation of charge transporting components in tri-block polymers

Abstract

9,9-Di-n-hexylfluorene-co-anthracene (DHF-ANT) random copolymer and triphenylamine (TPA)- and oxadiazole (OXA)-containing tri-block copolymers along with a crosslinked TPA polymer are used to fabricate single- and double-layer light emitting diodes (LEDs). In both single-layer and double-layer devices, TPA hole transporting components improve hole injection and transport, leading to improved device performance when low work function calcium (Ca) is used as the cathode, whereas OXA electron transporting components improve electron injection when high work function aluminum (Al) is used. This suggests that DHF-ANT copolymer and DHF-ANT blocks in the two tri-block polymers are hole-limited in devices with Ca cathodes, and electron-limited with Al cathodes. Furthermore, double-layer devices including a separate hole transporting crosslinked TPA layer increase device efficiencies by at least one order in magnitude over the corresponding single-layer devices, due to the improved charge injection, charge confinement and charge recombination.