A large improvement in performance of MEH-PPV-based light-emitting diodes has been demonstrated with a new n-type, regio-regular, conjugated copolymer containing 3,3'- dialkylbithiophene and bis(phenylquinoline) moieties in the main chain (see Figure). The good solubility of the copolymer in both aprotic organic solvents and protonic acid solvents has enabled the ready fabrication of multilayer light-emitting devices.