Fe$_{2}$MCh$_{4}$ (M=Si,Ge, Ch=S,Se): optical, electrical properties and defects

Fe$_{2}$MCh$_{4}$ (M=Si,Ge, Ch=S,Se) are proposed as solar absorber materials, as a single phase, stable alternative to FeS$_{2}$ pyrite. Native defects have high formation energy in the band gap and no Fermi level pinning is predicted by DFT. External defect calculations, including B,Al,Ga,In, N, P, As, Sb, Bi, O, Se, predict substantial effect on the bulk electronic properties.