Epoxy catalyzed sol–gel method for pinhole-free pyrite FeS2 thin films

• Photoactive pyrite thin films can be fabricated by a novel sol–gel route.
• The pyrite films are pinhole-free, phase-pure and without contaminants.
• The pyrite film can photosensitize titanium dioxide in a photoelectrochemical cell.

The uniform pinhole-free iron disulfide (FeS2) pyrite thin films were fabricated. In the first step the FeO(OH)x xerogel solution was synthetized by means of a novel epoxy catalyzed sol–gel method and next spin-coated onto various substrates to form the thin films. In the second step the xerogel coatings were annealed to yield hematite (α-Fe2O3) films, which were transformed into pyrite by chemical sulfurization. Among the main deposition parameters studied were the temperature of xerogel–hematite transformation and the optimal sufulrization temperature and duration. It has been observed that 15 min sulfurization at the temperature of 450 °C provided the pyrite films of sufficient quality. The estimated optical band gap of 0.98 eV is very close to the theoretical value of 0.95 eV. Auger electron spectroscopy showed almost ideal stoichiometry of FeS2. However a trace amount of oxygen (approximately 0.5 at.%) present in the film was still detected. The photoinduced functionality of the films was assessed based on photoelectrochemical experiments. In order to demonstrate the ability of pyrite to photosensitize a large band gap semiconductor, a bilayer system of TiO2 anatase/FeS2 pyrite was prepared. The highest photocurrent reached was 45 μA cm−2 at the light intensity of 10.5 mW cm−2.