Controlling the interface energetics of PCPDTBT by p-doping

The doping of organic semiconductors is a promising way for both improving the charge carrier transport and tuning the energy level alignment at interfaces. We study the influence of p-doping of the low band gap polymer PCPDTBT with F4-TCNQ on the energy level alignment in a prototype organic solar cell structure with ITO as an electrode material and the fullerene C₆₀ as electron acceptor material using Ultraviolet and X-ray photoelectron spectroscopy. As a consequence of the doping, a Quasi-Ohmic contact at the interface to ITO is formed, whereas the energy level alignment to C₆₀ is almost not affected. In contrast to a related system, we observe a depletion of the dopant at the polymer surface. The change of the energy level alignment only at the electrode interface might be advantageous for the application in organic solar cell devices.