Cryst. Res. Technol., 1–7 (2013) / DOI 10.1002/crat.201200484 Synthesis and single crystal growth of SnS by the Bridgman-Stockbarger technique T. Sorgenfrei*, F. Hofherr, T. Jauß, and A. Cr¨ oll Crystallography - Institute of Earth and Environmental Sciences, University of Freiburg, Hermann-Herder-Str. 5, 79104 Freiburg, Germany Received 30 November 2012, revised 31 January 2013, accepted 4 February 2013 Published online 5 March 2013 Key words tin monosulﬁde, synthesis, Bridgman growth, single crystal, characterization, X-ray diffraction, photoluminescence. SnS is a promising candidate as PV absorber material according to the material properties and the Loferski diagram, but despite the numerous publications on this material, the intrinsic material properties are widely unknown and the theoretical possible values for efﬁciency are still far away from those achieved in reality. Due to the fact that this material is mostly grown as thin ﬁlm material, bulk research is rare. The material synthesis and the melt growth of tin monosulﬁde (SnS) by using Bridgman-Stockbarger technique have been investigated in this study. After ﬁrst growth experiments produced polycrystalline SnS, a signiﬁcant reduction of the growth velocity lead to samples with a high amount of single crystalline material. These samples were investigated in detail regarding the structural and optical properties by using XRD/HRXRD, chemical etching and photoluminescence. C  2013 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim 1 Introduction Tin monosulﬁde (SnS) appears to be a promising candidate as a photovoltaic (PV) absorber material due to its favorable direct bandgap of ≈1.3 eV and, therefore, its high absorption coefﬁcient (α> 10 cm −1 ) for photons [1], its chemical stability, the availability and low cost of the elements tin (Sn) and sulfur (S), and its nontoxic properties. The current effort in photovoltaics is to reduce the costs per Watt, i.e. to reduce material consumption and productions costs per solar cell and to increase the efﬁciency. While silicon is abundant, the efﬁciency of PV cells of this material is close to their efﬁciency limit, due to their less than ideal absorptivity based on the indirect bandgap and the low absorption coefﬁcient. Other thin ﬁlm PV cells like CdTe/CdS or CIGS/CdS depend on the critical materials tellurium, cadmium, or indium, respectively. These elements handicap the reduction of production costs. According to the review paper of L. M. Peter [2] the search for new photovoltaic materials, which contain cheaper raw materials and lead reduced production costs, is absolutely necessary. Despite the fact, that in this paper SnS is not mentioned concretely as a possible alternative PV material, due to the there listed requirements - non-toxic material, due to recycling costs, in-line processing, thin ﬁlm fabrication, and low cost and very good availability of the elements - SnS is one of the most promising absorber materials. SnS crystallizes in an orthorhombic structure with the lattice parameters a = 0.398 nm, b = 0.433 nm, and c = 1.118 nm [3–5] and can be described as a double layer stacking of Sn and S atoms parallel to the c-axis. While the in-plane Sn-S bonding is relatively tight, the bonding between the layers in c-direction is of the van der Waal’s type and therefore the bond strength is much lower. This layer-type character leads to a relatively low hardness of the material (Mohs’ hardness ≈2) and to good cleavage properties along the (001) planes. SnS shows p-type electrical conductivity and it has a theoretical light conversion efﬁciency >24% according to the Loferski diagram [6]. However, available information on the electronic properties of SnS is often inconsistent and mostly derived from polycrystalline thin ﬁlms studies, crystallized far away from thermodynamic equilibrium conditions. Thin ﬁlms of SnS have been deposited using different techniques such as spray pyrolysis [7,8], ∗ Corresponding author: e-mail: tina.sorgenfrei@fmf.uni-freiburg.de C  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim