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