Green light-emitting polyfluorenes were synthesized by Suzuki polycondensation via introducing dibenzothiophene-S,S-dioxide-(di-)tri-phenylamine (G(1) and G(2)) moieties and dibenzothiophene-S,S-dioxide (SO) unit into the polyfluorene backbone, respectively. PF-SO-G copolymers show a high thermal stability and a moderate photoluminescence quantum yield in the range of 20-40%. The lowest unoccupied molecular orbital (LUMO) levels reduce with increasing the content of SO unit in the polymers. The efficient energy transfer from fluorene segment to G(1) or G(2) unit occurred in the PL process, and the EL emission peaked at about 510 nm was exclusively from G(1) or G(2) unit. Incorporating SO unit into the polymer backbone makes the device performances improved. The maximal luminous efficiency of 9.0 cd A(-1) with the CIE coordinates of (0.27, 0.56) was obtained for PF-SO15-G(2)5 based on a single-layered device of ITO/PEDOT:PSS/polymer/CsF/Al. And the polymers (PF-SO15-G5)s exhibited a dramatic LE stability at high current densities, even though at the current density of 200 mA cm(-2), the luminous efficiencies only dropped 10%. SO unit lowers the LUMO level, balances the injection and transportation of both electron and hole in the polymers, and therefore improves the device performances. The hole- and electron-only devices show that the hole and electron flux are well balanced, which demonstrates that (PF-SO15-G5)s are bipolar polymers with a balanced charge carrier transport. (C) 2012 Elsevier Ltd. All rights reserved.