Tuning iron pyrite thin film microstructure by sulfurization of columnar iron precursors

• Published in: Solar energy materials and solar cells 2013-10, Vol.117, p.306-314
• Main Authors: LaForge, Joshua M., Gyenes, Balazs, Xu, Sijia, Haynes, Landon K., Titova, Lyubov V., Hegmann, Frank A., Brett, Michael J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Convertors; Direct energy conversion and energy accumulation; Electric power plants; Electrical engineering. Electrical power engineering; Electrical machines; Electrical power engineering; Electro-optical materials; Energy; Exact sciences and technology; Iron pyrite; Microstructures; Miscellaneous; Natural energy; Photoelectric conversion; Photovoltaic conversion; Semiconductors; Solar cells. Photoelectrochemical cells; Solar energy; Sulfurization; Thin films
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2013.06.028

Iron pyrite is a promising material for photovoltaic power production due to low material extraction and processing costs and high optical absorption. Reliable production of photovoltaic grade iron pyrite thin films has, however, been challenging. One potential fabrication route is the direct conversion of iron-to-iron pyrite by sulfur annealing (sulfurization). Bulk iron thin films are used typically but they can suffer from cracking or delamination. Herein we report the sulfurization of porous, columnar Fe films deposited with Glancing Angle Deposition (GLAD), which allows us to control the inter-column spacing (void-fraction) of the precursor film. We show that the morphology and microstructure of the iron pyrite films are strongly affected by the void-fraction. By precisely tuning the void-fraction of the precursor film at 82° oblique angle incidence deposition we can produce iron pyrite films with increased crystallite sizes >100nm with a uniform, crack-free, facetted granular microstructure. Large crystallites may reduce carrier recombination at grain boundaries, which is attractive for photovoltaic devices. Further increasing the void-fraction produces a columnar iron pyrite structure. We also report composition, electrical and optical characterization including a 27ps lifetime of photocarriers measured with ultrafast optical-pump/THz-probe. Structured, porous precursors offer an alternate route to control microstructure and film stress during fabrication of iron pyrite thin films. [Display omitted] •We sulfurized columnar Fe films to form single-phase iron pyrite (FeS2) films.•Inter-column spacing influences iron pyrite microstructure.•Column spacing at α=82° produces large-grained, uniform, and robust pyrite films.•Large column spacing relaxes conversion stress, eliminating cracking or buckling.•We report composition, electronic properties and photocarrier dynamics.