Atomic Layer Deposition of Tin Monosulfi de Thin Films

Thin fi lm solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se) 2 and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfi de (SnS). In this report, pure, stoichiometric, singlephase SnS fi lms were obtained by atomic layer deposition (ALD) using the reaction of bis( N , N′- diisopropylacetamidinato)tin(II) [Sn(MeC(N- i Pr) 2 ) 2 ] and hydrogen sulfi de (H 2 S) at low temperatures (100 to 200 ° C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption ( α > 10 4 cm − 1 ) is observed throughout the visible and near-infrared spectral regions. The fi lms are p-type semiconductors with carrier concentration on the order of 10 16 cm − 3 and hole mobility 0.82–15.3 cm 2 V − 1 s − 1 in the plane of the fi lms. The electrical properties are anisotropic, with three times higher mobility in the direction through the fi lm, compared to the in-plane direction.