The possibility to tune optical constants of porphyrins, only by varying the core substituents of the molecules, endorse them as promising thin film materials for dye-sensitized- or hybrid molecular heterojunction- solar cells. For the design and improvement of such optical devices involving porphyrin layers, exact knowledge of the optical properties is desirable. Here, thermally grown thin films of different meso-tetraphenyl porphyrins (i.e. H2TPP, NiTPP, and CoTPP) on silicon are assessed by spectroscopic ellipsometry and atomic force microscopy. Optical constants were determined in the near-IR to near-UV spectral range. A detailed discussion of the optical bands and the related electronic transitions is performed. (C) 2014 Elsevier B.V. All rights reserved.