Polycrystalline SnS, Sn2S3, and SnS2 were deposited onto glass substrates by vapor transport deposition, with the stoichiometry controlled by deposition temperature. In addition, epitaxial growth of orthorhombic SnS(010) films on NaCl(100) with thicknesses up to 600 nm was demonstrated. The in-plane [100] directions of SnS and NaCl are oriented approximately 45° apart, and the translational relationship between SnS and NaCl was predicted by density functional theory. The epitaxial SnS is p-type with carrier concentration on the order of 1017 cm−3 and Hall hole mobility of 385 cm2 V−1 s−1 in-plane. It has indirect and direct bandgaps of 1.0 and 2.3 eV, respectively.

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Edge-on SEM images of SnS sheets demonstrating the thickness distribution of (a) the 190°C product and (b) the final 300°C product.

The power conversion efficiency of quantum-dot-sensitized solar cells (QDSSCs) hinges on interfacial charge transfer. Increasing quantum dot (QD) loading on the TiO2 anode has been proposed as a means to block recombination of electrons in the TiO2 to the hole transport material; however, it is not known whether a corresponding increase in QD-mediated recombination processes might lead to an overall higher rate of recombination. In this work, a 3-fold increase in PbS QD loading was achieved by the addition of an aqueous base to negatively charge the TiO2 surface during Pb cation deposition. Increased QD loading improved QDSSC device efficiencies through both increased light absorption and an overall reduction in recombination. Unexpectedly, we also found increased QD size had the detrimental effect of increasing recombination. Kinetic modeling of the effect of QD size on interfacial charge transfer processes provided qualitative agreement with the observed variation in recombination lifetimes. These results demonstrate a robust method of improving QD loading, identify the specific mechanisms by which increased QD deposition impacts device performance, and provide a framework for future efforts optimizing the device architecture of QDSSCs.

The SnS absorber layer in solar cell devices was produced by vapor transport deposition (VTD), which is a low-cost manufacturing method for solar modules. The performance of solar cells consisting of Si/Mo/SnS/ZnO/indium tin oxide (ITO) was limited by the SnS layer's surface texture and field-dependent carrier collection. For improved performance, a fluorine doped tin oxide (FTO) substrate was used in place of the Mo to smooth the topography of the VTD SnS and to make bifacial solar cells, which are potentially useful for multijunction applications. A bifacial SnS solar cell consisting of glass/FTO/SnS/CdS/ZnO/ITO demonstrated front- and back-side power conversion efficiencies of 1.2% and 0.2%, respectively.