KEYWORDS: Pyrite, Iron, Solar energy, Crystals, Metalorganic chemical vapor deposition, FT-IR spectroscopy, Thin films, Absorption, Chemical analysis, Solar cells
Thin polycrystalline films of iron disulfide have been grown on different substrates by chemical vapour deposition. The films were characterized using optical absorption and TEM. RBS and EDAX analysis has been used to explore the chemical stoichiometry. XRD and FTIR allowed the identification of both FeS2 phases pyrite and marcasite. A novel method for sensitization of highly porous Ti02 elecrodes with ultra thin (10-20 nm) polycrystalline films of FeS2 (pyrite) is presented. Photoelectrochemical solar cell using the above electrode generated high photovoltage of up to 600mV compared with single crystalline electrode (200 mV). In this device the semiconductor with a small band gap and high absorption coefficient (FeS2 pyrite; EG = 0.9 eV; a = 6 x 105 cm-1) absorbs the light and injects electrons into the conduction band the wide band gap semiconductor (Ti02 anatase; EG = 3.2 eV). Regeneration of holes is taking place by electron transfer from redox system in the electrolyte.
KEYWORDS: Pyrite, Iron, Thin films, Semiconductors, Absorption, Solar cells, Metalorganic chemical vapor deposition, Solar energy, Thin film solar cells, Oxides
Pyrite (Fe52) has been investigated as a promising new absorber material for thin film solar cell
applications because of its high optical absorption coefficient of 1OL cm1, and its bandgap of 0.9 to 1.0 eV. Thin
layers have been prepared by Metal Organic Chemical Vapor Deposition, MOCVD, Chemical Spray Pyrolysis, CSP,
Chemical Vapor Transport, CVT, and Sulfurization of Iron Oxide films, 510. It is postulated that for the material
FeS2, if x is not zero, a high point defect concentration results from replacing 2 dipoles by single S atoms. This
causes the observed photovoltages and solar conversion efficiencies to be lower than expected. Using the Fe-O-S
ternary phase diagram and the related activity plots, a thermodynamic understanding is formulated for the resulting
composition of each of these types of films. It is found that by operating in the oxide portion of the phase diagram,
the resulting oxidation state favors pyrite formation over FeS. By proper orientation of the grains relative to the
film surface, and by control of pinholes and stoichiometry, an efficient thin film photovolatic solar cell material
could be achieved.
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