Electron injection and electroluminescence investigation of organic light-emitting devices based on a Sn/Al cathode

Organic light-emitting devices (OLEDs) with the Sn/Al cathode have been fabricated. The structure of the devices is ITO/CuPc(12 nm)/NPB(60 nm)/Alq3(60 nm)/Sn(2.8 nm)/Al(120 nm). It is found that the presence of a thin tin (Sn) layer at the organic–aluminum (Al) interface can enhance both electron injection efficiency and electroluminescence when compared to OLEDs with only Al cathode. An Ag/Al bilayer cathode structure is also tested, and the similar results can be obtained. The improvement is believed to be due to two factors: (1) the enhancement of the electron density of the Sn or Ag layer; (2) the Sn or Ag layer in part prevents the Al atoms from diffusing into the organic layer. Al/Sn–Alq3–Sn/Al and Al–Alq3–Al devices have also been fabricated. It is shown that the nature of the interface is not equivalent for metal-on-Alq3 and Alq3-on-metal.