Energy Level Alignment of Organic Semiconductor/Metal Interfaces: Effect of Polar Self-Assembled Monolayers at the Interface

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2832306· OSTI ID:959870

Demirkan, K; Mathew, A; Weiland, C; Yao, Y; Rawlett, A; Tour, J; Opila, R

We determined the shifts in the energy levels of {approx} 15 nm thick poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] films deposited on various substrates including self-assembled monolayer (SAM) modified Au surfaces using photoelectron spectroscopy. As the unmodified substrates included Au, indium tin oxide, Si (with native oxide), and Al (with native oxide), a systematic shift in the detected energy levels of the organic semiconductor was observed to follow the work function values of the substrates. Furthermore, we used polar SAMs to alter the work function of the Au substrates. This suggests the opportunity to control the energy level positions of the organic semiconductor with respect to the electrode Fermi level. Photoelectron spectroscopy results showed that, by introducing SAMs on the Au surface, we successfully increased and decreased the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. Our study showed that when a substrate is modified by SAMs (or similarly by any adsorbed molecules), a new effective work function value is achieved; however, it does not necessarily imply that the new modified surface will behave similar to a different metal where the work function is equal to the effective work function of the modified surface. Various models and their possible contribution to this result are discussed.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 959870
• Report Number(s): BNL--82856-2009-JA
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Vol. 128; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALIGNMENT
ELECTRODES
ENERGY LEVELS
FERMI LEVEL
INDIUM
ORGANIC SEMICONDUCTORS
PHOTOELECTRON SPECTROSCOPY
SUBSTRATES
TIN OXIDES
WORK FUNCTIONS
national synchrotron light source