Finely tailored performance of inverted organic photovoltaics through layer-by-layer interfacial engineering.

Control over interfacial properties in organic photovoltaics (OPVs) is critical for many aspects of their performance. Functionalization of the transparent conducting electrode, in this case, indium tin oxide (ITO), through an electrostatic layer by layer (eLbL) approach with cationic N,N′-bis[2-(trimethylammonium)ethylene] perylene-3,4,9,10-tetracarboxyldiimide (PTCDI+) and anionic poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (PEDOT:PSS–), led to high control over the surface properties. The films were studied through a variety of surface and spectroscopic techniques, including X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, atomic force microscopy (AFM), and ellipsometry. The work function of modified ITO was measured by UV photoelectron spectroscopy (UPS) and showed oscillating values with respect to odd–even layer numbers; the strong odd–even effect is due to the differing electronic characteristics of the top layer, either PTCDI+ or PEDOT:PSS–. The modified ITO electrode...