Gaseous oxidation and compensating reduction of lutetium bis-phthalocyanine and lutetium phthalo-naphthalocyanine films

Abstract Thin films are deposited from lutetium bisphthalocyanine (LuPc 2 ) and lutetium phthalo-naphthalocyanine (LuPNc) that are intrinsic, easily oxidizable, molecular semiconductors. Oxidation of the films by NO 2 or Br 2 vapours is studied by visible absorption spectroscopy on “neutral” and oxidized films and by indashsitu measurements of conductivity and sorbed dopant mass uptake. Exposures of the oxidized LuPc 2 and LuPNc films to NH 3 lead to a conductivity increase or decrease depending on the oxidation degree of the films. The whole set of results is in agreement with a model that describes the existence of a conductivity maximum in LuPc 2 and LuPNc during oxidation as the consequence of both a trapping process of the charge carriers and a reduction of their mobility when the concentration of oxidized phthalocyanine molecules becomes too high.