Controlling energy levels and Fermi level en route to fully tailored energetics in organic semiconductors

Organic semiconductors have yet to achieve simultaneous control over both the energy levels and Fermi level, which was a key breakthrough for inorganic electronics. Here, we combine two approaches from band engineering and molecular doping to demonstrate controlled shifts in ionisation potential and Fermi level of an organic thin film. We experimentally investigate the doping efficiency of a ternary blend system consisting of two host molecules, ZnPc and F8-ZnPc, and the p-dopant F6–TCNNQ. We explain the observed doping behaviour with a statistical model based on energy level shifts of both host and dopant materials, resulting from the quadrupole moments of all involved molecules. We thereby demonstrate that band tuning crucially affects the doping process in organic semiconductors. The practice of comparing host and dopant energy levels must consider the long-range electrostatic shifts, arising from the quadrupole interactions to consistently explain the doping mechanism in organic semiconductors.