Iron pyrite thin films synthesized from an Fe(acac)3 ink

Area of Science:

• Materials Science
• Solid State Physics
• Photovoltaics

Background:

• Iron pyrite (FeS2) is an earth-abundant material with potential for thin-film solar cells.
• Previous fabrication methods have faced challenges in achieving desired film properties.

Purpose of the Study:

• To develop a solution-phase deposition method for fabricating high-quality iron pyrite films.
• To characterize the structural, compositional, optical, and electrical properties of these films.
• To compare these films with those produced by chemical vapor deposition.

Main Methods:

• Solution-phase deposition using an iron(III) acetylacetonate molecular ink.
• Sequential annealing in air, H2S, and sulfur gas.
• Characterization using X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy (XPS).
• Optical measurements and density functional theory (DFT) modeling.

Main Results:

• Phase-pure, large-grain, uniform polycrystalline pyrite films were successfully fabricated.
• Solution-deposited films showed different elemental compositions and smaller optical band gaps (0.87 ± 0.05 eV) compared to CVD films.
• Marcasite (orthorhombic FeS2) polymorph was found to have a band gap at least as large as pyrite.
• All films exhibited p-type transport, with properties consistently governed by a common defect or surface layer.

Conclusions:

• Solution-phase deposition is a viable method for producing iron pyrite films for solar cell applications.
• The optical and structural properties of pyrite and marcasite are comparable.
• The electrical transport properties of FeS2 thin films are universally limited, suggesting a need to address defect or surface states.