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Electronic and optical properties of FeSe2 polymorphs: solar cell absorber

Electronic and optical properties of semiconducting FeSe2 polymorphs (marcasite and pyrite) were evaluated using density functional theory with norm-conserving pseudopotential. Marcasite and pyrite of FeSe2 show indirect band gaps of 0.86 eV and 0.67 eV respectively. Absorption coefficient is high over a wide range of optical spectrum, indicating that these materials are exploitable as solar cell absorber. Marcasite FeSe2 is found to be optically anisotropic, whereas pyrite is isotropic. Mulliken Bond Population analysis shows mixed ionic-covalent nature of bonding for both polymorphs. Effective masses of electrons and holes were also calculated, which reinforce the semiconducting nature of FeSe2