Tunable optical constants of thermally grown thin porphyrin films on silicon for photovoltaic applications

• Thin porphyrin films were grown by vacuum thermal evaporation on silicon.
• Optical and morphological properties are assessed by ellipsometry and AFM.
• Optical constants in porphyrin films can be tuned by varying core substituents.

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.

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