Doping of organic semiconductors induced by lithium fluoride/aluminum electrodes studied by electron spin resonance and infrared reflection-absorption spectroscopy

Abstract

We report our investigations on the chemical doping mechanisms induced by LiF|Al electrodes evaporated onto fullerene thin films. Electron spin resonance (ESR) and infrared reflection-absorption spectroscopy (IRRAS) are utilized to characterize C60|Al and C60|LiF|Al interfaces. ESR spectra show that deposition of LiF followed by Al generates C60 radical anions and also the presence of an additional paramagnetic species of lower concentration that is present in all C60 films regardless of LiF. IRRAS clarifies the mechanism occurring at the C60|LiF|Al interface, showing that interaction between LiF and C60 followed by deposition of Al causes LiF clusters to chemically dissociate.