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.
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)