Tuning of metal work functions with self-assembled monolayers

Bert de Boer; Afshin Hadipour; Remko Foekema; Teunis van Woudenbergh; Magda M. Mandoc; Valentin D. Mihailetchi; Paul W. M. Blom

doi:10.1117/12.546046

8 September 2004 Tuning of metal work functions with self-assembled monolayers

Bert de Boer, Afshin Hadipour, Remko Foekema, Teunis van Woudenbergh, Magda M. Mandoc, Valentin D. Mihailetchi, Paul W. M. Blom

Author Affiliations +

Proceedings Volume 5464, Organic Optoelectronics and Photonics; (2004) https://doi.org/10.1117/12.546046
Event: Photonics Europe, 2004, Strasbourg, France

Abstract

Tuning the work functions of metals was demonstrated by chemically modifying the metal surface through the formation of chemisorbed self-assembled monolayers (SAMs) derived from 1H,1H,2H,2H-perfluorinated alkanethiols and hexadecanethiol. The ordering inherent in the SAMs creates an effective, molecular dipole at the metal/SAM interface, which increased the work function of Ag (Φ_Ag ~4.4 eV) to 5.5 eV (ΔΦ ~ 1.1 eV) for 1H,1H,2H,2H-perfluorinated alkanethiols. Hexadecanethiol on the other hand shifted Φ_Ag toward 3.8 eV (ΔΦ ~ 0.6 eV) and raised the energy barrier for hole injection. These SAMs on Au were less efficient. 1H,1H,2H,2H-perfluorodecanethiol raised ΦAu (4.9 eV) by 0.5 eV to 5.4 eV, whereas hexadecanethiol decreased Φ_Au by only 0.1 eV. These chemically modified electrodes were applied in the fabrication of pLEDs and the hole conduction of MEH-PPV was investigated. An ohmic contact for hole injection between a silver electrode functionalized with the perfluorinated SAMs, and MEH-PPV with a HOMO of 5.2 eV was established. Conversely, a silver electrode modified with a SAM of hexadecanethiol lowered Φ_Ag to 3.8 eV, creating an efficient energy barrier for hole injection. This method demonstrates a simple and attractive approach to modify and improve metal/organic contacts in organic electronic devices like LEDs and photovoltaic cells.

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Bert de Boer, Afshin Hadipour, Remko Foekema, Teunis van Woudenbergh, Magda M. Mandoc, Valentin D. Mihailetchi, and Paul W. M. Blom "Tuning of metal work functions with self-assembled monolayers", Proc. SPIE 5464, Organic Optoelectronics and Photonics, (8 September 2004); https://doi.org/10.1117/12.546046

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