Energy level alignment of polythiophene/ZnO hybrid solar cells

Energy level alignment at interfaces is critical for fundamental understanding and optimization of organic photovoltaics (OPV) as band offsets of the donor and acceptor materials largely determine the open circuit voltage (V_oc) of the device. Using ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPS), we examined the correlation between energy level alignment and photovoltaic properties of a model bilayer hybrid solar cell incorporating electrodeposited polythiophene (e-PT) films on ZnO planar substrates. The electrolyte anion (BF₄^-, PF₆^-, ClO₄^- or CF₃SO ₃^-) in the electrodeposition solution was found to have a strong influence on the e-PT film morphology and adhesion, the energy level alignment at the interface, and ultimately the V_oc of the photovoltaic devices.