Switching the Electronic Properties of ZnO Surfaces with Negative T‐Type Photochromic Pyridyl‐dihydropyrene Layers and Impact of Fermi Level Pinning. Issue 10 (8th April 2019)

• Record Type: Journal Article
• Authors: Wang, Qiankun; Ligorio, Giovanni; Schlesinger, Raphael; Diez‐Cabanes, Valentin; Cornil, David; Garmshausen, Yves; Hecht, Stefan; Cornil, Jérôme; List‐Kratochvil, Emil J. W.; Koch, Norbert
• Is Part Of: Advanced materials interfaces. Volume 6:Issue 10(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-04-08
• Subjects: density functional theory -- dihydropyrene -- photochromism -- photoemission spectroscopy -- ZnO; Materials science -- Periodicals; 620.11
• DOI: 10.1002/admi.201900211
• Languages: English
• ISSNs: 2196-7350

Abstract

Abstract: Remote control of the electronic energy levels by external stimuli such as light will enable optoelectronic devices with improved or additional functionalities. Here, it is demonstrated that the electronic properties of ZnO interfaced with negative T‐type photoswitches, that is, pyridyl‐dihydropyrene (Py‐DHP), can indeed be photomodulated. The process of forward switching of Py‐DHP with green light from an isomer with a low energy gap to an isomer with a wider one is followed by a thermally activated backward transfer. Using photoemission spectroscopy and density functional theory modeling, it is shown that Py‐DHP ring closure/opening reactions result in a reversible shift of frontier occupied molecular levels by 0.7 eV with respect to the Fermi level. Notably, in both molecular configurations, the energy level alignment at ZnO/Py‐DHP interfaces is governed by a Fermi level pinning at the lowest unoccupied molecular level. Moreover, upon switching, an increase in the ionization energy for Py‐DHP multilayers compared to that of a monolayer is observed. This is attributed to a different preferred molecular orientation in monolayer versus multilayers. The results show that a dynamic tuning of the energy level alignment at inorganic/organic interfaces by external stimuli is feasible and will aid the development of photoprogrammable optoelectronic devices. Abstract : The electronic properties of a ZnO surface can be reversibly modulated by a layer of photochromic pyridyl‐dihydropyrene (Py‐DHP) molecules. The dynamic reversible switching is facilitated via light and heat stimuli, respectively. The energy level alignment at the hybrid ZnO/Py‐DHP interface is found to be governed by Fermi level pinning at the lowest unoccupied molecular level.