Hole doping by molecular oxygen in organic semiconductors: Band-structure calculations

The sensitive effect of O-2 adsorption on the electronic properties of organic semiconductors is investigated by band structure calculation. O-2 can actually p-dope the host materials even without illumination, i.e., a ground state property, in the circumstance of saturated coverage. Due to hybridization between O-2 and polymer, Fermi level of the oxygenated system is pinned at the nearly half-filled oxygen band and overlap with host valence band. The doping depends critically on the ionization potential. Each O-2 can dope more than 0.1 hole in dark and a full charge-transfer excitation around 2.3 eV photon energy is predicted.