Modification of Work Function of Au(111) Upon Adsorption of PEG(thiol)
Jongmin Kim a, Andris Gulans a, Claudia Draxl a
a Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany
Proceedings of Interfaces in Organic and Hybrid Thin-Film Optoelectronics (INFORM)
València, Spain, 2019 March 5th - 7th
Organizers: Natalie Stingelin, Henk Bolink and Michele Sessolo
Poster, Jongmin Kim, 088
Publication date: 8th January 2019

Poor charge injection/extraction at an organic-electrode interface is a crucial issue for organic electronics as this severely limits the device performance. A work-function modification of the electrodes is the most efficient way to overcome this shortcoming. In recent years, experimental studies have revealed that polyethylene glycol(PEG) used as an interlayer between the electrodes and the organic materials improves the performance of devices by reducing the work-function of the cathode [1]. In this computational work, we investigate thiol-terminated polyethylene glycol(PEG(thiol)) adsorbed on the Au(111) surface. In order to consider van der Waals interactions, we employ the DFT-D2 [2] as well as the many-body dispersion (MBD@rsSCS) [3] methods. In both cases, we find that a monolayer of PEG(thiol) molecules reduces the work-function of the metal. This effect is smaller for odd numbers of repeat units of the PEG backbone and larger for even numbers. The screening effects included in MBD@rsSCS, but disregarded in DFT-D2, noticeably impact the adsorption geometry. This, in turn, determines the amount of the work-function change, where the values range from -0.39 eV to -1.11 eV in case of the former method and from -0.24 eV to -0.95 eV in case of the latter one.

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