Which is better as a buffer layer for organic light‐emitting devices, CsF or LiF?

Abstract

AbstractThe device characteristics of organic light‐emitting devices (OLEDs) based on tris‐(8‐hydroxyquinoline) aluminum (Alq3) with a thin layer of cesium fluoride (CsF) or lithium fluoride (LiF) inserted at the organic layer and the Mg:Ag cathode or the indium tin oxide (ITO) anode and organic layer were investigated. One‐nm thick CsF or LiF can enhance the electron injection when it was inserted only between the emitting layer and the Mg:Ag alloy cathode. When 1‐nm thick CsF or LiF was inserted between the ITO anode and the organic hole‐transport layer, LiF can block hole injection and the corresponding device exhibited a high current efficiency of 2.95 cd/A; however, the current efficiency of the device inserting CsF is as low as 0.93 cd/A. Compared to the performances of the five types of devices, CsF is a better buffer layer than LiF between Mg:Ag and Alq3 in OLEDs. One‐nm thick LiF can also improve OLED performance as an anode buffer layer. But 1‐nm thick CsF is harmful to OLED performance when acting as an anode buffer layer.