First-principles Study On FeS₂ And CoS₂ Doping Of Pyrite

In this paper,we investigate the electronic and optical properties of pyrite FeS2,as well as electronic and magnetic properties of pyrite CoS2 with the DFT of the first principles calculation.We find the theory evidence of increasing the photoelectric conversion efficiency of pyrite FeS2 and producing perfect half-meat of pyrite CoS2.Increasing the band gap of FeS2 with O doping and producing half-meat with N doping for CoS2 in theory are realized.Iron pyrite(FeS2),due to its high abundance,nontoxicity and strong optic absorption(??105 cm-1 hv>1.3 eV),has aroused plenty of intense interests as a bright promising photovoltaic material.However,its photoelectric conversion efficiency is lower than 3%.The most limiting factor for a high efficiency is closely related to its low open-circuit voltage(OCV),(less than 0.2 eV)which directly limited FeS2 for photovoltaic applications in industry.Therefore,to exploit the potential applicable pyrite-based photovoltaics,searching for feasible and suitable ways to increase the band gap of FeS2 is greatly necessary.So we find the method of modulating the band gap and optic band gap of FeS2 with the orbital-projected band structure and the charge density.We find:(1)The band gap of FeS2 is mainly controlled by the Fe-t2g states of the VBM and low intensity states S ppa*of CBM;(2)The optical band gaps of both FeS2 and doped FeS2 systems originate mainly from electric dipole transitions between the Fe-t2g states of the VBM and the bottom of the Fe-eg states in the conduction bands instead of the low intensity and long trailing S(Se)pp?*states of the CBM.Pyrite-type CoS2 is an itinerant electron ferromagnet below Tc ?120K has been vertified by experiments.In these years,CoS2 as a nearly half metal has been widely accepted by researchers,which has stimulated extensive efforts to research CoS2 and its compounds to exploit potential half-metal ferromagnets(HMF).However,Which subband crosses the EF in the spin-down channel and destroys the half-metallicity of pure CoS2 has debated for a long time in theory.There has been a lack of a theory that could modulate the CoS2 turn into the perfect half-metal all the time.So in the third section of the paper,we study the orbital-projected band structure and charge density.We find that the CBM of CoS2 in spin-down channel is mainly contributed by the low intensity state of S pp?*which extends below the EF and destroys the half-metallicity of CoS2.So we obtained the theory evidence and realize a perfect HMF with 12.5%concentration of N doping.