Solution-processed VOx prepared using a novel synthetic method as the hole extraction layer for polymer solar cells

In this study, we report solution-processed vanadium oxide (s-VOx) as the hole extraction layer (HEL) for polymer solar cells (PSCs). A s-VOx thin film is prepared simply by the spin-coating of ammonium metavanadate ammonal water solution on the surface of indium tin oxide (ITO) coated glass substrates, followed by thermal annealing at 210 degrees C for 5 minutes in air. The scanning Kelvin probe measurement indicates that the work function of the s-VOx HEL is -5.3 eV, which allows most of the conjugated polymers to form an Ohmic contact with the s-VOx HEL, resulting in a large open-circuit voltage for PSCs. It is found that PSCs incorporated with the s-VOx HEL possess a comparable power conversion efficiency and better shelf-stability with those incorporated with the poly (3,4-ethylenedioxythiophene) : poly(styrenesulfonate) anode buffer layer. Thus, our method provides a simple approach to prepare a solution-processed s-VOx HEL for higher performance PSCs.