Atmospheric-Pressure Chemical Vapor Deposition of Iron Pyrite Thin Films

Iron pyrite (cubic FeS ₂ ) is a promising candidate absorber material for earth-abundant thin-fi lm solar cells. In this report, single-phase, large-grain, and uniform polycrystalline pyrite thin fi lms are fabricated on glass and molybdenum-coated glass substrates by atmospheric-pressure chemical vapor deposition (AP-CVD) using the reaction of iron(III) acetylacetonate and tert -butyl disulfi de in argon at 300 ° C, followed by sulfur annealing at 500-550 ° C to convert marcasite impurities to pyrite. The pyrite-marcasite phase composition depends strongly on the concentration of sodium in the growth substrate and the sulfur partial pressure during annealing. Phase and elemental composition of the fi lms are characterized by X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy. The in-plane electrical properties are surprisingly insensitive to phase and elemental impurities, with all fi lms showing p -type, thermally activated transport with a small activation energy ( ̃ 30 meV), a roomtemperature resistivity of ̃ 1 Ω cm, and low mobility. These ubiquitous electrical properties may result from robust surface effects. These CVD pyrite thin fi lms are well suited to fundamental electrical studies and the fabrication of pyrite photovoltaic device stacks.