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 V ₂O ₅ hole-extraction-layer on top of the active organic layer. The V ₂O ₅ 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 V ₂O ₅ 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 V ₂O ₅ layers is similar to that of thermally evaporated V ₂O ₅ layers which have been exposed to ambient air. Optimization of the sol gel process leads to inverted OSCs with solution based V ₂O ₅ layers that show power conversion efficiencies similar to that of control devices with V ₂O ₅ layers prepared in high-vacuum.