Transition between energy level alignment regimes at a low band gap polymer-electrode interfaces

The energy level alignment at interfaces between a low band gap conjugated polymer and various electrodes is investigated using ultraviolet photoemission spectroscopy. When the electrode work function is lower (higher) than the negative (positive) polaronic level of the polymer, the Fermi level is pinned to the negative (positive) polaronic level. These Fermi level pinning regimes suggest a spontaneous electron transfer from or towards the electrode resulting in an interfacial dipole of different orientation. On the contrary, when the substrate work function is intermediate, there is no charge transfer and the energy level alignment across the interface follows the Schottky-Mott limit. (c) 2006 American Institute of Physics.