  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.
