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Through empirical observations, sodium(Na) has been identified as a benign contaminant

in some thin-filmsolar cells. Here, we intentionally contaminate thermally evaporated tin

sulfide (SnS)thin-films withsodium and measure the SnS absorber properties and solar cell 

characteristics. The carrier concentrationincreases from 2 × 1016 cm−3 to 4.3 × 1017 cm−3 

in Na-doped SnSthin-films, when using a 13 nm NaCl seed layer, which is detrimental for SnS 

photovoltaic applications but could make Na-doped SnS an attractive candidate in

thermoelectrics.The observed trend in carrier concentration is in good agreement with

density functional theory calculations, which predict an acceptor-type NaSn defect with

low formation energy.

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