Figure 5 : Fractional slope parameters and band bending versus interface dipole.

From: Organic semiconductor density of states controls the energy level alignment at electrode interfaces

Figure 5

(a) Injection barriers Δe for electrons (left axis) and Δh for hole (right axis) as a function of effective substrate work function Φeff for a d=10 nm pentacene film. The peak shape of the HOMO- and LUMO-derived DOS in the first layer is successively varied from pure Gaussian over Voigt to pure Lorentzian. (b) Electron potential energy −eV(z) within a d=10 nm pentacene film and a Φeff of 5.3 eV. Changing the peak shape of the HOMO- and LUMO-derived DOS in the first layer from pure Gaussian over Voigt to pure Lorentzian leads to a collapse of the spatially extended band-bending region to an interface dipole across the first molecular layer. (c) Injection barriers Δe for electrons (left axis) and Δh for holes (right axis) as a function of effective substrate work function Φeff for a d=10 nm pentacene film. The DOS of the first layer is kept fixed to a Lorentzian peak shape of width 0.25 eV, whereas the standard deviations σH/L of the Gaussian peak shapes in all subsequent layers increase from 0.1 eV up to 0.4 eV. Although the range of linearity decreases succeedingly, the value of the slope parameter S<1 remains unchanged.