17% Non-Fullerene Organic Solar Cells with Annealing-Free Aqueous MoO_x

A charge transport layer based on transition metal-oxides prepared by an anhydrous sol–gel method normally requires high-temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll-to-roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing-free solution-processable metal-oxide is essential for the large-scale commercialization. In this work, a room-temperature processable annealing-free “aqueous” MoO_x solution is developed and applied in non-fullerene PBDB-T-2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing-free MoO_x with excellent electrical properties is successfully developed. The PBDB-T-2F:Y6 solar cell with the general MoO_x prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoO_x is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB-T-2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoO_x exhibits comparable performance of 17.0%. In addition, the solar cell with annealing-free aqueous MoO_x exhibits better performance and stability without high-temperature annealing compared to the solar cells with PEDOT:PSS.