We investigate the electronic interface properties of an organic bilayer heterojunction solar cell, built of CuPc/BPE-PTCDI as donor/acceptor system. Band alignment of this interface and interface potentials were measured using synchrotron induced photoemission spectroscopy (SXPS) on stepwise deposited BPE-PTCDI on doped and non doped CuPc. Using non doped CuPc at thermodynamic equilibrium the bands bend at the interface in a direction that hinders dissociation of geminate pairs.
As a measure to form a band bending that supports geminate pair separation p-doping of CuPc is tested. As dopant WO3 was applied being a promising material for p-doping of CuPc due to its high ionization potential. At the doped CuPc/BPE-PTCDI interface the internal field is actually reversed now driving holes in CuPc and electrons in BPE-PTCDI away from the interface.