Iron Pyrite Thin Films Synthesized from an Fe(acac)₃ Ink

Abstract

Iron pyrite (cubic FeS2) is a promising candidate absorber material for earth-abundant thin-film solar cells. Here, we report on phase-pure, large-grain, and uniform polycrystalline pyrite films that are fabricated by solution-phase deposition of an iron(III) acetylacetonate molecular ink followed by sequential annealing in air, H2S, and sulfur gas at temperatures up to 550 °C. Phase and elemental compositions of the films are characterized by conventional and synchrotron X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy (XPS). These solution-deposited films have more oxygen and alkalis, less carbon and hydrogen, and smaller optical band gaps (E(g) = 0.87 ± 0.05 eV) than similar films made by chemical vapor deposition. XPS is used to assess the chemical composition of the film surface before and after exposure to air and immersion in water to remove surface contaminants. Optical measurements of films rich in marcasite (orthorhombic FeS2) show that marcasite has a band gap at least as large as pyrite and that the two polymorphs share similar absorptivity spectra, in excellent agreement with density functional theory models. Regardless of the marcasite and elemental impurity contents, all films show p-type, weakly activated transport with curved Arrhenius plots, a room-temperature resistivity of ~1 Ω cm, and a hole mobility that is too small to measure by Hall effect. This universal electrical behavior strongly suggests that a common defect or a hole-rich surface layer governs the electrical properties of most FeS2 thin films.

Increasing the band gap of FeS2 by alloying with Zn and applying biaxial strain: A first-principles study

“…Experimentally, the epitaxial growth of FeS 2 and Zn-doped FeS 2 thin film for photovoltaic applications prefer [1 0 0] orientation on the substrate [19,20,27,28]. Consequently, biaxial strain may be introduced on the Zn-doped FeS 2 thin films, and the band gap of Zn-doped FeS 2 may be adjusted.…”

Electrochemical deposition of Fe–S–O thin films

“…Many methods have been used for the preparation of thin pyrite films, such as low pressure chemical vapor deposition [3], spray pyrolysis [4], sulfurization of electrodeposited films [5,6], sulfurization of sputtered [7] or vacuum evaporated [8,9] iron films, sol-gel [10,11], and chemical bath deposition [12]. More recently, the use of ink technology was also reported, where precursor films of molecular inks composed of iron complexes and elemental sulfur were spin-coated and annealed [13]. The band gap of FeS 2 is considered to be 0.95 eV, which is in fact smaller than the optimum one for solar cells (about 1.5 eV [14]).…”

Scientific and Technological Assessment of Iron Pyrite for Use in Solar Devices

“…Several vapor-phase and solution-processing techniques to synthesize iron pyrite were reported, which include sulfurization of iron and iron-oxide thin films, [10,34,[41][42][43][44] electrodeposition, [45] chemical vapor deposition, [7,[46][47][48] spray pyrolysis, [49,50] sputtering, [51,52] hydrothermal method, [53] and hot-injection method. [27,29,54,55] Theq uality of the pyrite thin film is mostly governed by the sulfurization process in almosta ll cases whereas organic ligands used in many chemical synthesis methods play an importantr ole in controlling the size of nanosized pyrite particles.…”