Dynamically Switching the Electronic and Electrostatic Properties of Indium-Tin Oxide Electrodes with Photochromic Monolayers: Toward Photoswitchable Optoelectronic Devices

The chemical modification of electrodes with organic materials is a common approach to tuning the electronic and electrostatic landscapes between interlayers in optoelectronic devices, thus facilitating charge injection at the electrode/semiconductor interfaces and improving their performance. The use of photochromic molecules for surface modification allows a 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 to ITO, the packing density of molecules, their orientation, and work function modification of the ITO surface due to SAM deposition. Upon illumination with UV 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 upon modification with a monolayer of photochromic molecules, which could be used to fabricate ITO-based photoswitchable optoelectronic devices.