Synthesis of Iron Pyrite Film through Low Temperature Atmospheric Pressure Chemical Vapor Deposition
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Synthesis of Iron Pyrite Film through Low Temperature Atmospheric Pressure Chemical Vapor Deposition Siva P Adusumilli1, 2, Tara P Dhakal1 and Charles R Westgate1, 2 1
Center for Autonomous Solar Power (CASP), State University of New York at Binghamton,
Vestal, NY 13850, U.S.A. 2
Dept. of Electrical Engineering, State University of New York at Binghamton, Vestal, NY
13850, U.S.A.
ABSTRACT Pyrite phase of FeS2 has attracted substantial attention in the field of thin film solar technology because of its high optical absorption coefficient (~5 x 105 cm-1 at hν > 1.3eV) and the band gap of 0.95 eV. In this research, we have grown highly pure iron pyrite films using a low temperature atmospheric pressure chemical vapor deposition technique. The synthesis temperature is in the range of 375-400°C and Di-tert-butyl disulfide (TBDS) is used as the sulfur precursor. TBDS is a safe and low cost sulfur source unlike H2S, which is highly toxic and requires extreme care in handling. The films obtained were uniform and free from common impurity phases such as troilite and marcasite. The FeS2 films grown earlier with CVD synthesis and sulfurized using H2S had pinholes and contained secondary phases like marcasite and troilite. The FeS2 pyrite phase was confirmed using various characterization techniques that included SEM, EDS, XRD and XPS.
INTRODUCTION In recent years growing attention has been paid to new low cost and high performance materials for solar cells. Iron pyrite has excellent light absorption properties and its band gap in near infra-red region helps to tap energy from sun even at nights. Iron pyrite (FeS2), which is sometimes termed as fool’s gold by its metallic luster, can really become more valuable if it can be grown in single phase thin film form through a safe, stable, and cheaper method. Once this method is realized, FeS2 can be used as a p-type absorber layer in a thin film solar cell device. With the suitable energy band gap of 0.95 eV and indirect transition at 1.03 eV [1, 2], and absorption coefficient remarkably high at ~ 105 cm-1, it is a potential candidate apt for photovoltaics. In a recent report [3], 23 different inorganic photovoltaic materials including CdTe, CdS, CZTS, CIGS, Zn3P2, and FeS2 were compared for their availability and cost effectiveness. Pyrite appears to be the leader in its availability and the raw material cost of pyrite is lower than 0.000002 cents/W. Because of its abundance in nature, the mass production of solar cell using iron pyrite at very affordable cost will be possible. Pyrite has previously been synthesized using different methods like MOCVD, sputtering, spray
pyrolysis [1,4,5] which involve high process temperatures and unsafe precursors like H2S, and the synthesized films lacked phase purity. In this work, we report a pyrite phase which is free from marcasite and/or troilite and is grown using low temperature chemical vapor deposition at atmospheric pressure. Di-tert-butyl disulfide (TBDS) is used as the sulfur precursor, which is a safe and low cost sulfur sourc
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