Effect of water and oxygen on the electronic structure of the organic photovoltaic

Effects of water and oxygen exposures on electronic structures of the bathocuproine (BCP)/fullerene (C ₆₀) interface were studied by photoemission spectroscopies. C ₆₀ in BCP/C ₆₀ interface prepared under ultrahigh vacuum (UHV) shows a downward energy level bending of 0.3 eV. The energy level bending of C ₆₀ significantly increases to ∼0.8 eV upon exposure to water moisture or oxygen gas at 5 × 10 ^-6 Torr for 30 min. The results suggest the formation of electron traps at the C ₆₀/BCP interface upon water or moisture exposure. The decrease in electron transporting barrier between the lowest unoccupied molecular orbital (LUMO) of C ₆₀ and metal-induced gap states in BCP upon metal deposition encourages the charge leakage from cathode to C ₆₀. Charge recombination in C ₆₀ upon water or oxygen exposure is also discussed. © 2012 American Chemical Society.