Direct Chemical Vapor Deposition Synthesis of Phase-Pure Iron Pyrite (FeS₂) Thin Films

Abstract

Resurgent interest in iron pyrite (FeS2) as an earth-abundant, nontoxic semiconductor for solar applications has resulted in many attempts to grow phase-pure thin films via chemical vapor deposition (CVD). However, all thin films grown via CVD or sulfidation to date have contained marcasite phase or other iron sulfide impurities. Here, we report the use of metallic cobalt pyrite (cattierite, CoS2) thin films as an ideal substrate leading to the first direct growth of phase-pure iron pyrite thin films via atmospheric pressure CVD. This synthesis was achieved by reacting FeCl3 and ditert butyl disulfide (TBDS) at 400–450 °C. The products were confirmed as phase-pure iron pyrite using X-ray diffraction (XRD), Raman spectroscopy, and energy dispersive X-ray spectroscopy (EDS). In addition to phase-purity, the synthesis produced crystal domains >1 μm and a conformal coating 3–5 μm thick, which are attributed to the <2% lattice mismatch of the isostructural cattierite substrate. The surface was characterized by ultraviolet and X-ray photoelectron spectroscopy (UPS & XPS) and the electrical properties by electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. The direct growth of a phase-pure iron pyrite film on a conductive substrate provides the most convenient configuration so far for potential solar cells.