Antimony-Doped Tin(II) Sulfide Thin Films

Thin-film solar cells made from earth-abundant, inexpensive, and nontoxic materials are needed to replace the current technologies whose widespread use is limited by their use of scarce, costly, and toxic elements. Tin monosulfide (SnS) is a promising candidate for making absorber layers in scalable, inexpensive, and nontoxic solar cells. SnS has always been observed to be a p-type semiconductor. Doping SnS to form an n-type semiconductor would permit the construction of solar cells with p-n homojunctions. This paper reports doping SnS films with antimony, a potential n-type dopant. Small amounts of antimony (1%) were found to greatly increase the electrical resistance of the SnS. The resulting intrinsic SnS(Sb) films could be used for the insulating layer in a p-i-n design for solar cells. Higher concentrations (5%) of antimony did not convert the SnS(Sb) to low-resistivity n-type conductivity, but instead the films retain such a high resistance that the conductivity type could not be determined. Extended X-ray absorption fine structure analysis reveals that the highly doped films contain precipitates of a secondary phase that has chemical bonds characteristic of metallic antimony, rather than the antimony–sulfur bonds found in films with lower concentrations of antimony.United States. Dept. of Energy. Sunshot Initiative (Contract DE-EE0005329)National Science Foundation (U.S.) (Grant CBET-1032955

Theoretical and Experimental Investigations on the Growth of SnS van der Waals Epitaxies on Graphene Buffer Layer

We present theoretical and experimental investigations on the growth of SnS van der Waals epitaxies (vdWEs) on graphene buffer layer (GBL). Local density approximation (LDA) was used to evaluate the bond length disorder, binding energies, and growth orientations for SnS deposited on crystalline semiconductor substrates with and without the GBL. Strong bond length disorder is observed for SnS deposited directly on GaAs substrates, whereas in the case where a GBL is used the disorder is substantially reduced. First-principle calculations indicate two favored growth orientations for SnS deposited on GBL resulting in 12 distinct peaks in the azimuthal hard X-ray diffraction (HXRD) scan due to the structural symmetry of the GBL. The results stipulate formation of strong chemical bonds at the GaAs/SnS interface while the interaction between SnS and the underlying GBL is dominated by vdW force. Nevertheless this vdW force is shown to be strong enough to induce favored nucleation orientations for the SnS and is essential for the observed improvement in the crystallinity of the films