Synthesis and device performance of new efficient blue copolymers containing biphenylenevinylene and triphenyldiamine

Abstract

A series of light-emitting copolymers, poly(N (4),N (4)-bis-(4-phenyl)-N (4),N (4')-bis-[4-(2-ethylhexyloxy)phenyl]-biphenyl-4,4'-diamine-co-1,2-bis(4'-phenyl)-1-(9aEuro(3),9aEuro(3)-dihexyl-3-fluorenyl)ethane), P(BPBEPA-co-BPHFE) with different ratios (5%, 12.5%, 30%) of BPBEPA was synthesized using a Yamamoto coupling reaction. The structures of the copolymers were examined using various spectroscopic methods. The obtained copolymers showed blue fluorescence in 487-496 nm. The introduction of arylamine gave the copolymers good hole injection ability as well as good solubility and thermal stability with high T (g) . The EL performance of these copolymers were investigated from the devices structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT), doped with poly(styrenesulfonic acid) (PEDOT:PSS) (40 nm)/polymer (60 nm)/Ca (50 nm)/Li (100 nm). The copolymers exhibited maximum EL peaks in a range from 484 to 489 nm. The maximum current efficiency of 2.17 cd/A, maximum power efficiency of 1.24 lm/W and lower turn-on voltage of 3.5 V for P(BPBEPA(12.5)-co-BPHFE87.5) were observed. The enhanced EL performance of P(BPBEPA(12.5)-co-BPHFE87.5) can be explained by charge balance due to the introduced hole transporting BPBEPA.