Investigating the stability of defects in MoO3 and its role in organic solar cells

In this work, the generation and stability of defects in molybdenum oxide (MoO3) is studied in detail. We found that the defects generated by annealing are typically more stable against re-oxidation by plasma treatment when compared with the sputtered defects. Against air exposure, the annealed defects are also highly stable showing little re-oxidation even after long exposures. The sputtered defects however showed prominent decrease of the defect states and the kinetics can be classified into two regimes with different rate constants. The reason behind the difference in stability can be attributed to the different types of bonding for the generated defects. Following this, we fabricated two forward solar cells with an as-deposited MoO3 and another with intentionally generated defects. We obtained a higher short circuit current (Jsc) when the generated defects are present and the overall efficiency is increased by ∼50%. We propose that the presence of the defects acted as an additional pathway for holes extraction and highlights the important role that surface defects play in enhancement of device performances.

► Distinguished difference of annealed and sputtered defects in MoO3.
► Showed higher stability of annealed defects against re-oxidation.
► Demonstrated role of surface defects in enhancing short circuit current.
► Proposed a mechanism of how surface defects enhanced hole extraction.