Figure 1. Doping of pentacene studied by ultraviolet photoelectron spectroscopy.

Pentacene (PEN) is doped by F₆TCNNQ (p-doping) and W₂(hpp)₄ (n-doping) (HBEC: high binding energy cutoff). The shift of the HOMO of pentacene relative to the Fermi level (at 0 eV) is strong already at a low doping concentration of 0.5 wt%. For p-doping, the HOMO shifts towards the Fermi level and for n-doping away from the Fermi level.