In this article, we demonstrated the OLED incorporating a transport layer composed of lithium carbonate (Li₂CO₃) doped into the 2-methyl-9, 10-di (2-naphthyl) anthracene (MADN) as electron injection material. In our devices, an OLED with n-doping structure ITO/NPB (40nm)/Alq₃ (40nm)/Li₂CO₃: MADN (5nm, 25%)/LiF (1nm)/Al (140nm) accomplished maximum luminance of 20760 cd/m² and current efficiency of 4.878 cd/A. By contrast, the device without doping Li₂CO₃ ITO/NPB(40nm)/Alq₃ (40nm)/ MADN (5nm)/LiF (1nm)/Al (140nm) achieved a maximum luminance of 15530 cd/m² and current efficiency of 3.922 cd/A. The device of the standard one ITO/NPB(40nm)/Alq₃ (40nm)/LiF (1nm)/Al (140nm) only achieved a maximum luminance of 18450 cd/m² and current efficiency of 3.134 cd/A.

The experiment results show that the transport layer with appropriate doping can efficiently enhance the electron injection, leading to more balanced concentration of electrons and holes. Compared with the standard sample, the maximum luminance and current efficiency are increased by12.5% and 55.6%, respectively.