Structure–Property Relationship of Phenylene-Based Self-Assembled Monolayers for Record Low Work Function of Indium Tin Oxide

Abstract

Studying the structure-property relations of tailored dipolar phenyl and biphenylphosphonic acids, we report self-assembled monolayers with a significant decrease in the work function (WF) of indium-tin oxide (ITO) electrodes. Whereas the strengths of the dipoles are varied through the different molecular lengths and the introduction of electron-withdrawing fluorine atoms, the surface energy is kept constant through the electron-donating N, N-dimethylamine head groups. The self-assembled monolayer formation and its modification of the electrodes are investigated via infrared reflection absorption spectroscopy, contact angle measurements, and photoelectron spectroscopy. The WF decrease in ITO correlates with increasing molecular dipoles. The lowest ever recorded WF of 3.7 eV is achieved with the fluorinated biphenylphosphonic acid.

Tetrapodal Diazatriptycene Enforces Orthogonal Orientation in Self-Assembled Monolayers

“…6,7 To achieve a maximum work function shift (WFS), the molecular dipole has to be perpendicular to the surface. [8][9][10] Additionally, spatial and lateral control of the SAM's functional group is crucial for many single-molecule devices such as molecular wires, switches, rotors, sensors or redox-active or photochromic moieties. [11][12][13][14][15][16][17][18][19][20][21] Multipods allow generally a reasonable control of molecular orientation.…”

Nano-films of carbo-benzene derivatives: Scanning probe microscopy analysis and prospects of use in organic solar cells

“…Indeed, all atoms are arranged in such a way that the unit-cell axes of the packing arrangement remain unchanged within the domain itself. Benneckendorf et al [47] reported the structure-property relationships of dipolar phenyl and biphenylphosphonic acid: the strengths of the dipoles are varied through the inclusion of electron-withdrawing fluorine atoms and the molecular length, however, the surface energy is kept constant through the electron-donating N,N-dimethylamine fragment, which were able to form self-assembled monolayers on indium-tin oxide (ITO) electrodes modifying its work function (∅). In addition, quantum mechanical calculations showed that the dipole vector of N,Ndimethylaniline derivatives is orientated towards the electrode interface, directly influencing changes of the ∅ value [47].…”

“…Benneckendorf et al [47] reported the structure-property relationships of dipolar phenyl and biphenylphosphonic acid: the strengths of the dipoles are varied through the inclusion of electron-withdrawing fluorine atoms and the molecular length, however, the surface energy is kept constant through the electron-donating N,N-dimethylamine fragment, which were able to form self-assembled monolayers on indium-tin oxide (ITO) electrodes modifying its work function (∅). In addition, quantum mechanical calculations showed that the dipole vector of N,Ndimethylaniline derivatives is orientated towards the electrode interface, directly influencing changes of the ∅ value [47]. Meanwhile, by removing the methyl groups from the amino fragment, from NMe2 in 1 (quadrupolar) to NH2 in 2 (dipolar), the work function of the metal surfaces has been modified by the adsorption of SAMs, which form surface dipoles [48], as observed for 1 but also for the dithiolylidene-substituted carbo-quinoid 3.…”

From Electronic Structure to Design Principles for Photocathodes: Cu - Ba Alloys

“…It has previously been observed that organic dipole layers on Au and Ag reduced their WF, and a linear relationship existed between the size of the surface dipole moment and WF [43]. It has also been reported that the WF of an indium-tin oxide electrode could be reduced if the dipole vector due to a self-assembled monolayer (SAM) is pointing away from the electrode-SAM interface [44]. In the context of the current results, this suggests a general design principle for decreasing the WF of alloy surfaces by engineering structures with large interatomic charge transfer and surface dipoles.…”