Optical Spectroscopy during Growth of PTCDA-C60 Complex Thin Films

Abstract

Combined Raman and photoluminescence (PL) measurements were performed in situ and online during the formation of a PTCDA-C60 charge transfer (CT) complex film using organic molecular beam deposition. It is found that two different processes compete during growth, namely the formation of PTCDA-C60 CT complexes and the photopolymerization between C60 molecules. The CT complexes, formed instantaneously upon the co-deposition of two molecules, decompose as the C60 molecules forming the CT complexes undergo the photopolymerization with excess C60 molecules. At low coverage, 70% of PTCDA molecules in the film form CT complexes with C60. The rate of CT complex formation decreases dramatically with the beginning of the photopolymerization after 11 min of deposition. The results prove the importance of preventing the formation of C60−C60 pairs in order to keep the maximum ratio of CT complexes in the film under laser irradiation.