Enhancing the Performance of Inverted Organic Photovoltaics Using Cathode Interlayers Based on Solution-Processable Tetrabutylammonium Halides

High-performance inverted organic photovoltaics (OPVs) require the work function of transparent bottom cathodes to be low, which can be efficiently achieved by inserting an ultrathin interlayer to form an interface dipole. Herein, solution-processable tetrabutylammonium halides (TBAXs, X = Cl, Br, and I) are employed as a cathode interlayer in inverted OPVs, leading to the disappearance of an S-shaped kink in their current density–voltage curves and increasing their open-circuit voltages and fill factors, which resulted in significantly enhanced power conversion efficiencies. Ultraviolet photoelectron spectroscopy measurements revealed that the work function of indium tin oxide (ITO) was considerably lowered in the presence of TBAX interlayers, resulting in efficient electron extraction from the C₆₀ acceptor to the ITO bottom cathode and increasing the built-in potential across devices. Thus, TBAXs are demonstrated to be promising materials for efficient cathode interlayer formation in inverted OPVs.