We present a dataset of the optical constants of α- and β-zinc(II)-phthalocyanine (ZnPc). They were determined accurately from transmission and differential reflectance spectra, with the surface roughness taken into account. For this purpose, thin films were prepared on quartz glass substrates via physical vapor deposition and characterized by ultraviolet-visible (UV-Vis) spectroscopy before as well as after a well-defined annealing process. Kramers-Kronig consistency of the optical constants obtained was checked by means of a numerical algorithm. 1. Introduction Zinc(II)-phthalocyanine (ZnPc) is a promising material for organic electronics, especially photovoltaic devices. It has already been applied in prototypes of solar cells [1–4]. Furthermore, it is already known that phthalocyanines (including ZnPc) can exist in multiple types of crystalline phases [5]; in particular, the metastable -ZnPc (higher electrical conductivity) and the stable -ZnPc (lower electrical conductivity) [6] need to be distinguished. Structural analysis of both phases and detailed information about the phase transition as shown in [7] are needed to set suitable constraints for a numerical model to determine the optical constants of - and -ZnPc. Once the optical constants are known, they can be used for modeling layer systems or even photovoltaic devices, or vice versa, for a nondestructive optical analysis of the crystallinity of ZnPc layers. Here, we present a reliable method for the determination of optical constants of organic thin films, where the surface roughness is taken into account. Finally, we present a detailed dataset of optical constants for polycrystalline - and -ZnPc covering an energy interval from 1.2？eV to 5.0？eV. 2. Methodology Thin films of ZnPc were prepared via physical vapor deposition on quartz glass. Quartz glass was used as substrate due to the low absorbance in a broad spectral range ( between 300？nm and 850？nm). After thorough in situ degassing, the ZnPc powder obtained from Sigma-Aldrich with 97% chemical purity was thermally evaporated from a ceramic crucible in a tungsten boat and deposited at a rate of 0.6？？/s under high vacuum conditions (pressure: ？mbar). To realize the growth of the phase, ZnPc was deposited on substrates kept at room temperature [8]. A phase transition from -ZnPc to -ZnPc upon annealing has been demonstrated in the literature [7, 9, 10]. Here, the stable -ZnPc phase was obtained from the metastable -ZnPc samples via annealing under ambient conditions for 3？h at 240°C and above. Films of both phases with different thicknesses
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