“…Iron pyrite (cubic β -FeS 2 , "fool's gold") is a remarkable semiconductor that has attracted much interest in various green energy fi elds, such as photoelectrochemical and photovoltaic solar cells, [1][2][3] batteries, [ 4 ] photoemission, [ 5 ] and photodiodes, [6][7][8][9] due to its strong light absorption ( α > 10 5 cm −1 for h ν > 1.3 eV), [ 10 ] a suitable bandgap (E g = 0.95 eV) and an adequate minority carrier diffusion length (100-1000 nm), [ 9,11 ] More importantly, earth abundance (Iron is the fourth most abundant element in the earth's crust), low-cost and non-toxicity of FeS 2 nanocrystals make them excellent candidates for developing cost-effective optoelectronic devices instead of inorganic semiconductors that possess non-sustainable elements. However, the low output efficiency of FeS 2 optoelectronic devices limits their broad applications, [ 8,[12][13][14] which has been attributed to the phase impurity or sulfur vacancies in the bulk and at the surface that generate electronic states within the bandgap.…”