NaSbS2 was recently proposed as a novel photovoltaic semiconductor with earth-abundant component elements,but its fundamental material properties have not been well studied.The systematical first-principles calculations for its electronic,optical and defect properties were carried out in the present study,and the results show that:i)NaSbS2 in the rocksalt-derived structure has a quasi-direct band gap and thus may have long minority carrier lifetime;ii) its absorption coefficients are as high as 10~4～10~5 cm-1 for the visible light and almost isotropic despite that the structure is distorted relative to the high-symmetry rocksalt structure;iii) the effective masses of the electron and hole carriers are anisotropic with much larger values along the z direction than in the x-y plane,and hence the orientational control of thin films should be important for enhancing the photovoltaic performance;iv) the valence and conduction band edges of NaSbS2 are close to those of CuGaSe2) so the n-CdS/pCuGaSe2 device structure can be inherited to form the n-CdS/p-NaSbS2 solar cells;v) the acceptor defects (NaSbantisites and Na vacancies) have very high concentration,making the synthesized NaSbS2 always be p-type;vi)the S-rich condition can suppress the formation of deep-level donor defects (S vacancies and SbNa antisites) and therefore should be adopted for fabricating high-efficiency NaSbS2 solar cells.
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