Inverted Organic Solar Cells with Sol–Gel Processed High Work-Function Vanadium Oxide Hole-Extraction Layers



For large-scale and high-throughput production of organic solar cells (OSCs), liquid processing of the functional layers is desired. We demonstrate inverted bulk-heterojunction organic solar cells (OSCs) with a sol–gel derived V2O5 hole-extraction-layer on top of the active organic layer. The V2O5 layers are prepared in ambient air using Vanadium(V)-oxitriisopropoxide as precursor. Without any post-annealing or plasma treatment, a high work function of the V2O5 layers is confirmed by both Kelvin probe analysis and ultraviolet photoelectron spectroscopy (UPS). Using UPS and inverse photoelectron spectroscopy (IPES), we show that the electronic structure of the solution processed V2O5 layers is similar to that of thermally evaporated V2O5 layers which have been exposed to ambient air. Optimization of the sol gel process leads to inverted OSCs with solution based V2O5 layers that show power conversion efficiencies similar to that of control devices with V2O5 layers prepared in high-vacuum.