Abstract
This study focuses on the hole transport layer of molybdenum trioxide (MoO(3)) for inverted bulk heterojunction (BHJ) organic photovoltaics (OPVs), which were fabricated using a combination of a spray coating and low-temperature annealing process as an alternative to the thermal evaporation process. To achieve a good coating quality of the sprayed film, the solvent used for solution-processed MoO(3) (S-MoO(3)) should be well prepared. Isopropanol (IPA) is added to the as-prepared S-MoO(3) solution to control its concentration. MoO(3) solutions at concentrations of 5 mg/mL and 1 mg/mL were used for the spray coating process. The power conversion efficiency (PCE) depends on the concentration of the MoO(3) solution and the spray coating process parameters of the MoO(3) film, such as flow flux, spray cycles, and film thickness. The results of devices fabricated from solution-processed MoO(3) with various spray fluxes show a lower PCE than that based on thermally evaporated MoO(3) (T-MoO(3)) due to a limiting FF, which gradually increases with decreasing spray cycles. The highest PCE of 2.8% can be achieved with a 1 mg/mL concentration of MoO(3) solution at the sprayed flux of 0.2 mL/min sprayed for one cycle. Additionally, S-MoO(3) demonstrates excellent stability. Even without any encapsulation, OPVs can retain 90% of their initial PCE after 1300 h in a nitrogen-filled glove box and under ambient air conditions. The stability of OPVs without any encapsulation still has 90% of its initial PCE after 1300 h in a nitrogen-filled glove box and under air conditions. The results represent an evaluation of the feasibility of solution-processed HTL, which could be employed for a large-area mass production method.