Electrode modification and interface engineering in organic light-emitting diodes

It is well known that the use of a cathode consisting of a thin LiF layer and a thick Al overlayer (∼100 nm) produces an excellent electron-injecting contact for organic light-emitting diodes (OLEDs). We report in this paper that the contact is formed as a result of the chemical reaction involving LiF, Al, and Alq, and the reacted layer is of the order of 1 nm or less. The shallow contact nature allows for a much greater flexibility in the design of cathode structures and extending its applications to various device configurations. By using the shallow contact, an ITO-free surface emitting OLED was prepared and shown to have superior electrical and optical characteristics.