Electrical characterization of Fermi level pinning in metal/3,4,9,10 perylenetetracarboxylic dianhydride interfaces

Abstract

Systematic studies of current injection from different metal electrodes to metal/3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) interfaces have been carried out. It has been observed that the barrier for carrier injection cannot be explained by simple vacuum alignment scheme. Moreover, injection barrier is almost independent of metal work function. These observations are explained by the changes of barrier height due to interface dipole barrier which compensate for the difference of work function of PTCDA and metals, leading to metal independent injection barrier and Fermi level pinning at metal/PTCDA interfaces.

Analysis of pinning effect at the Alq3/metal interface in organic light emitting diodes

“…4 Lots of work are in literature about the improvement of the cathode efficiency. [5][6][7][8][9][10][11][12][13] Several metals have been employed in OLEDs in order to increase the electron injection such as magnesium, calcium, aluminum, silver, antimony, and ytterbium; 5 carbon nanotubes 6 have shown an increasing of the electric field because of their geometry; transparent electrode 7 have been realized by using compounds of molybdenum obtaining low cathode sheet resistance and good device efficiency. Moreover, the usage of particular structures has been widely employed: microstructured cathode-semiconductor interfaces have been realized by the means of microimprinting techniques; 8 the adoption of LiF, C60, and CsF (Refs.…”

Small π-conjugated organic molecules based transistor and inverter with Cu electrodes

“…According to Mott-Schottky VLA rule, the energy barriers that control the electrons (holes) are entirely determined by U M and v(I). But, it has been found [4,14,15] as in case of metal/inorganic semiconductor interfaces, energy level alignment at interface departs from ideal situation, i.e. VLA.…”

“…Hence, the barrier for electrons at Au/F 16 CuPc and Cu/F 16 CuPc interfaces is 0.1 eV according to relation U Be = U M À (v À D). In this case, D completely compensates the difference between metal work function and v of F 16 CuPc, leading to Fermi level pinning [15,21]. Electronic states within energy gap between LUMO and HOMO due to chemical reactions between metal and organics, interdiffusion, metal induced gap states and several other poorly understood processes related to interface modifications, have been found to be responsible for Fermi level pinning.…”

“…Fig. 7f shows the cases in which Fermi level is pinned [14,15], i.e. U Be or U Bh does not depend on U M and has been observed in some OMSs.…”

“…At MOS interface, the barrier for electrons (U Be ) and holes (U Bh ) depend on the v and I of OMS, respectively. Depending on the degree to which the barriers for charge injection at MOS interface vary with metal work function (U M ), two extreme cases are considered: vacuum-level alignment (VLA) [14], known as Mott-Schottky limit and Fermi level pinning [14,15]. According to Mott-Schottky VLA rule, the energy barriers that control the electrons (holes) are entirely determined by U M and v(I).…”