Multilayer polymer light-emitting diodes are made using semiconducting polymers. An emissive polymer layer is cast from solution in an organic solvent, and a water-soluble (or methanol-soluble) conjugated copolymer is used for the electron transport layer (ETL) in the following device configuration: (indium tin oxide)/poly(3,4-ethylenedioxythiophene)/emissive polymer/ETL/Ba/Al. Devices with an ETL have significantly lower turn-on voltages, higher brightness values, and improved luminous efficiencies.