Three approaches were performed to achieve the charge balance in normal structure QLEDs so as to improve their external quantum efficiency: by inserting an ultra-thin PMMA electronic barrier layer between the lighting emitting layer and electron transport layer of QLED with the structure of ITO/HIL/HTL/QD/ETL/EIL/metal cathode;by optimizing the hole injection layer in the hole side to improve the probability of hole injection and transport; replacing the long chain ligands of quantum dots with short chain ones to help the charge injection and transport into the emitting layer, so as to improve the device performance. Another benefit of the ligand exchange is the improved solubility of quantum dots in orthogonal solvents of charge transport layers, which is essential for full-solution processed QLEDs.