The effect of substrate deposition temperature on the electrical and optical properties of C60 thin films

We report the effects of the substrate deposition temperature on the photovoltaic performance of fullerene (C60) thin films. These thin films were deposited via thermal evaporation at substrate temperatures from 20 to 250 °C. The optical and electrical properties of the films were dependent on the substrate deposition temperature, and improvements in film optical properties were noted for certain temperatures. Both the optical constants n and k and the dielectric constants show theoretical and experimental decreases with the substrate temperature due to the creation of crystalline structures in the thin films. Despite differences between the theoretical and experimental optical constants, the nature of the decrease is similar. The film porosity calculated from the optical constants increased more than 50% for greater substrate temperatures. The conductivity of the films also increased with the substrate temperature and the activation energy ranged from 0.25 to 0.31 eV. We demonstrate an increased energy gap with temperature using a Tauc-plot, and the photopic and solar transmittances improved with the increased substrate temperature during deposition.