A structure for high performance light emitting electrochemical cells comprises at least two active layers of mixed ionic/electronic conducting materials, at least one of which is electroluminescent. The active layers are sandwiched between ion blocking electrodes, typically metal and/or transparent conducting oxide, that are electrically but not ionically conductive. Application of bias to the electrodes results in the polarization of ions at the electrodes thereby generating a field to drive the injection of electronic carriers into the active layer. The injected electron and holes recombine within the active layers to emit light. The ability to balance electron and hole injection in the design of such devices provides for optimal light emission efficiency.