We report a novel solution-processible polymer, poly(2-dimethyloctylsilyl-1,4-phenylenevinylene) (DMOS-PPV) which shows a very high photoluminescence efficiency (60% for thin solid films). With the use of aluminium as cathode, an internal quantum efficiency as high as 2% has been obtained from bilayer diodes. The photoluminescence excitation measurement on a pristine film suggests constant efficiency for singlet intrachain exciton generation.