We studied the n-type doping effect of K deposited on tris(8- hydroxyquinoline) aluminum (Alq 3), which has been used for efficient organic semiconducting devices for the last decade. The K doped or inserted at the interface region of the Alq 3/cathode has shown highly enhanced device characteristics and yet, peculiarly, extra doping of K has always deteriorated the device properties. We study the interfacial electronic structures of the Alq 3-K system using in situ photoemission spectroscopy and a theoretical model to understand the origin of such deterioration. As the K doping progresses, the lowest unoccupied molecular orbital (LUMO) of pristine Alq 3 is gradually filled and it becomes an occupied gap state. This reduction of LUMO density of states makes the electron injection diminished, which is the origin of the device deterioration.
|Journal||Journal of Applied Physics|
|Publication status||Published - 2012 Feb 15|
Bibliographical noteFunding Information:
This work was supported by Brain Korea 21 (BK21) project of the ministry of Education, Science and Technology and by a research project of the National Research Foundation of Korea (Grant No. 2011-0004748).
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)