Complex Refractive Indices of Zinc Phthalocyanine, Fullerene C70, and Their Mixed Composition

Abstract

Spectral properties of organic semiconductors (zinc phthalocyanine (ZnPc), fullerene C70, and their mixture (ZnPc : C70) have been studied. The transmission spectra measured in the optical range of 240–1050 nm have been used to obtain spectral dependences of the complex refractive indices with application of numerical simulation methods. It is shown that the absorption spectrum of the mixed composition cannot be presented as a linear superposition of spectra of individual mixture components. The difference between the absorption spectrum of the mixture and superposition of the spectra of individual components is due to the interaction between zinc phthalocyanine and fullerene molecules. This interaction is most pronounced in the long-wavelength spectral region associated with the exciton excitations in ZnPc, where a significant increase in the absorption coefficient and the real part of the complex refractive index is observed.