Organometallic dimers: application to work-function reduction of conducting oxides

Area of Science:

• Organometallic Chemistry
• Materials Science
• Surface Science

Background:

• Modifying electrode work functions is crucial for efficient organic electronic devices.
• Ethoxylated poly(ethylenimine) (PEIE) is a common material for work function reduction.
• Exploring alternative, solution-processable reagents is of significant interest.

Purpose of the Study:

• To investigate the efficacy of pentamethyliridocene and ruthenium pentamethylcyclopentadienyl mesitylene dimers as solution-processable work function lowering reagents.
• To compare the performance of these organometallic dimers with PEIE.
• To elucidate the mechanism behind the work function reduction induced by the organometallic dimers.

Main Methods:

• Solution processing of (IrCp*Cp)2 and (RuCp*mes)2 dimers in toluene.
• Work function measurements of modified indium tin oxide (ITO), zinc oxide, and gold electrodes using photoelectron spectroscopy.
• Fabrication and characterization of C60 organic diodes with dimer-modified cathodes.

Main Results:

• Both (IrCp*Cp)2 and (RuCp*mes)2 effectively reduced the work functions of ITO, zinc oxide, and gold electrodes to 3.3-3.4 eV.
• The work function reduction is comparable to that achieved with spin-coated PEIE films.
• Reductions are attributed to interface dipoles formed by redox reactions between the dimer and negatively charged substrates, leading to submonolayers of IrCp*Cp(+) cations.
• C60 diodes with dimer-modified ITO cathodes exhibited similar electrical properties to those with PEIE-modified cathodes.

Conclusions:

• Organometallic dimers like (IrCp*Cp)2 are effective, solution-processable alternatives to PEIE for reducing electrode work functions.
• The mechanism involves the formation of interface dipoles via redox-induced cation formation.
• These findings offer a new strategy for optimizing electrode interfaces in organic electronic devices.