Surface polarity, water adhesion and wettability behaviors of iron pyrite

Abstract Earth abundant iron pyrite (FeS2) has attracted considerable attention as a potential non-toxic absorber material in lieu of widely used but toxic and relatively rare Indium containing CIGS and CdTe for thin-film solar cells. Research in this regard has been progressed in understanding its fundamental electronic, optical and chemical properties, while its surface polarity is rarely been studied. In this contribution, we have investigated the adhesion of water to determine the wettability (i.e. hydrophilic or hydrophobic) of naturally grown FeS2, and thereof, the polarity of the surface. FeS2 has a cubic crystal structure that grows and cleaves along its cubic faces. Based on the measurements using Sessile drop method, we have found that the surfaces of the pyrite phase of FeS2 crystals are intrinsically super-hydrophilic and highly polar. Our finding is corroborated with X-ray diffraction, Fourier Transform Infrared, Raman Spectroscopy, particle size determination, and contact angle measurements of the pyrite phase. The surface polarity would be a critical factor for choosing surface passivation protocols and type of contact materials as well as for interpreting surface field effects in the system for solar cell application with material heterojunctions.