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The chemical modification of electrodes with organic materials is a common approach to tune the electronic and electrostatic landscape between interlayers in optoelectronic devices, thus facilitating charge injection at the electrode/semiconductor interfaces and improving their performance. The use of photochromic molecules for the surface modification allows dynamic control of the electronic and electrostatic properties of the electrode and thereby enables additional functionalities in such devices. Here, we show that the electronic properties of a transparent indium tin oxide (ITO) electrode are reversibly and dynamically modified by depositing organic photochromic switches (diarylethenes) in the form of self-assembled monolayers (SAMs). By combining a range of surface characterization and density functional theory calculations, we present a detailed picture of the SAM binding onto ITO, the packing density of molecules, their orientation, as well as the work function modification of the ITO surface due to the SAM deposition. Upon illumination with ultraviolet and green light, we observe a reversible shift of the frontier occupied levels by 0.7 eV, and concomitantly a reversible work function change of ca. 60 meV. Our results prove the viability of dynamic switching of the electronic properties of the electrode with external light stimuli, which could be used to fabricate ITO-based photo-switchable optoelectronic devices.
Publication date: 
30 Nov 2018

Qiankun Wang, Valentin Diez-Cabanes, Simone Dell'Elce, Andrea Liscio, Björn Kobin, Hong Li, Jean-Luc Brédas, Stefan Hecht, Vincenzo Palermo, Emil JW List-Kratochvil, Jérôme Cornil, Norbert Koch, Giovanni Ligorio

Biblio References: 
arXiv preprint arXiv:1811.12741