n-Type doping of organic molecular electronic films

A. Kahn, Princeton University, USA

N-type Doping of Organic Molecular Films

N-type doping of organic materials is difficult because of the low electron affinity (~1.5 – 2.5 eV) of most electron transport materials (ETM) of interest. Dopants must have low ionization energy to transfer an electron to lowest unoccupied molecular orbital (LUMO) of the host, and are thus inherently unstable. Alkali cations are mobile and diffuses through the organic layer. Their small size leads to a fairly tightly bond cation-anion pair with the host molecule, resulting in strong electron localization. Larger, less mobile donors are therefore being pursued. We report here on the use of the strongly reducing molecule bis(cyclopentadienyl)-cobalt(II) (cobaltocene, CoCp2) (ionization energy = 4.0 eV) to n-dope an important ETM, a tris(thieno)hexaazaphenylylene derivative (THAP) [1]. UPS, inverse photoemission, ion scattering, X-ray photoemission and I-V measurements are used to characterize the energetics and transport properties of the doped system. We also describe on-going work using the even stronger reducing molecular agent decamethyl cobaltocene to n-dope phthalocyanines and pentacene.

Antoine Kahn received his Ph.D. in Electrical Engineering and Computer Science from Princeton University in 1978. He joined the Princeton faculty in 1979, and was promoted to the rank of Associate Professor in 1985 and Full Professor in 1991. His research is in the field of semiconductor surfaces and interfaces. Over the past twelve years, he and his group focused on the structural, electronic and chemical properties of surfaces and interfaces of organic molecular and polymer films, and the physics of molecular level alignment across interfaces. He has published over 260 regular and review articles. He is a Fellow of the AVS (1999) and APS (2002).