A highly efficient blue polymer light-emitting diode based on poly(9,9-di(2-(2-(2-methoxy-ethoxy)ethoxy)ethyl)fluorenyl-2,7-diyl) (PFOEO₃) by solvent vapour annealing the polymer emitting layer is fabricated in a bilayer device with Al cathode. High electroluminescent efficiency is achieved by balancing charge injection. Better contact interface between the polymer and the cathode was formed by making chain conformation reoriented with solvent vapour exposure. The effect of solvent vapour exposure on the potential barrier height of the interface is estimated using the Richardson–Schottky model. The maximum efficiency that was achieved was 2.3 cd A⁻¹ for the vapour exposed device compared with 0.9 cd A⁻¹ for the untreated pristine device.