1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) is known to improve hole injection when inserted between the hole transport layer and the indium tin oxide (ITO) anode in organic light emitting devices. To clarify the origin of the improvement, the interfacial electronic structures between N,N′-diphenyl-N, N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′ diamine (NPB, typical hole transport layer) and ITO with a NTCDA insertion layer were explored. The NTCDA layer generates an interface state when it interacts with ITO and also induces large interface dipole. The interface state assists hole transport and the interface dipole pulls entire energy levels of NPB up, reducing the hole injection barrier.
Bibliographical noteFunding Information:
This work was supported by BK21 project of the ministry of Education, Science and Technology and a research project of NRF (Grant No. 2011-0004748).
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)