Organic Dipole Layers for Ultralow Work Function Electrodes

Abstract

The alignment of the electrode Fermi level with the valence or conduction bands of organic semiconductors is a key parameter controlling the efficiency of organic light-emitting diodes, solar cells, and printed circuits. Here, we introduce a class of organic molecules that form highly robust dipole layers, capable of shifting the work function of noble metals (Au and Ag) down to 3.1 eV, that is, ∼1 eV lower than previously reported self-assembled monolayers. The physics behind the considerable interface dipole is elucidated by means of photoemission spectroscopy and density functional theory calculations, and a polymer diode exclusively based on the surface modification of a single electrode in a symmetric, two-terminal Au/poly(3-hexylthiophene)/Au junction is presented. The diode exhibits the remarkable rectification ratio of ∼2·10(3), showing high reproducibility, durability (>3 years), and excellent electrical stability. With this evidence, noble metal electrodes with work function values comparable to that of standard cathode materials used in optoelectronic applications are demonstrated.

Interplay among work function, electronic structure and stoichiometry in nanostructured VOx films

“…52 The low WF of suboxides could be extremely useful if they are used as electron injection layer in an OSD, since as in OLED the optimization of the cathode WF may increase the efficiency. 7,53 We would like to point out that the straight line trend of eq. 3 is not valid for x=0.…”

OH-terminated two-dimensional transition metal carbides and nitrides as ultralow work function materials

“…Recently, new techniques have been developed successfully to grow self-assembled monolayers of organic molecules with low work functions, which are eco-friendly [23] although they might be unstable thermally.…”

Adsorption of oriented carborane dipoles on a silver surface

“…Surface properties can be effectively adjusted by the adsorption of molecules which modify the interface electronic structure . This facile approach can be used to adjust the work function (WF) value of a particular substrate by the adsorption of molecules with relatively large, inherent dipole moments, or to probe the electronic structure and orientation of some new molecules immobilized on a well‐known substrate surface . Self‐assembled monolayers (SAMs) on metal surfaces are two‐dimensional periodic materials with physicochemical properties influenced by the choice of constituents with characteristic properties, such as dimensions, structure, and chemical composition .…”