Thermally Stable Solution Processed Vanadium Oxide as a Hole Extraction Layer in Organic Solar Cells

Low-temperature solution-processable vanadium oxide (V(2)O(x)) thin films have been employed as hole extraction layers (HELs) in polymer bulk heterojunction solar cells. V(2)O(x) films were fabricated in air by spin-coating vanadium(V) oxytriisopropoxide (s-V(2)O(x)) at room temperature without the need for further thermal annealing. The deposited vanadium(V) oxytriisopropoxide film undergoes hydrolysis in air, converting to V(2)O(x) with optical and electronic properties comparable to vacuum-deposited V(2)O(5). When s-V(2)O(x) thin films were annealed in air at temperatures of 100 °C and 200 °C, OPV devices showed similar results with good thermal stability and better light transparency. Annealing at 300 °C and 400 °C resulted in a power conversion efficiency (PCE) of 5% with a decrement approximately 15% lower than that of unannealed films; this is due to the relative decrease in the shunt resistance (R(sh)) and an increase in the series resistance (R(s)) related to changes in the oxidation state of vanadium.