Growth of Large Single Crystals of n-Type SnS from Halogen-Added Sn Flux

Abstract

We report the growth of large Cl-doped and Brdoped SnS single crystals from a molten Sn-based flux. Compared with the small and lamellar undoped SnS crystals, the addition of SnCl 2 or SnBr 2 halogen sources in the flux substantially enhanced lateral growth along the (100)-plane and vertical growth. The maximum size of the obtained single crystals reached a diameter and thickness of 16 mm and 0.7 mm for the Cl-doped SnS and 24 mm and 1.0 mm for the Br-doped SnS, respectively. The X-ray rocking curves and the X-ray back-reflection Laue patterns indicated a high crystal quality. The obtained crystals were further characterized via electrical measurements, including electrical conductivity and Hall measurements, optical absorption spectroscopy, and X-ray and ultraviolet photoelectron spectroscopies. Both the Cl-doped and Br-doped SnS single crystals exhibited degenerate n-type conductivity with a high electrical conductivity of 11.1 S cm −1 for Cl-doped SnS and 18.9 S cm −1 for Br-doped SnS along the (100)-plane at 300 K. Furthermore, the photoelectron spectroscopy results also indicated n-type conductivity. The large single crystals of n-type SnS obtained in this work would enable the fabrication of p-n homojunction SnS solar cells via the deposition of p-type SnS thin films.

SnS Homojunction Solar Cell with n‐Type Single Crystal and p‐Type Thin Film

“…In addition, Table 2 shows the detailed photovoltaic characteristics of the SnS solar cells, i.e., series resistance (R S ), shunt resistance (R Sh ), ideality factor of a diode (n), and the reverse saturation current (J 0 ), which were obtained from the J-V relationship of the single-junction solar cells (Section S2, Supporting Information), [29] together with the thickness of SnS layer (d). As shown in Table 2, the V OC of the homojunction solar cells fabricated in this study was remarkably high after the heterojunction solar cells fabricated by Pawar et al in 2020 ((V OC ¼ 405 mV with η ¼ 3.72%), [16] The properties of undoped SnS thin film are those of the film deposited on the SiO 2 glass substrate under the same conditions as the films deposited on the n-type SnS single crystals; b) The study by Kawanishi et al [22] Chua et al in 2019 ((V OC ¼ 400 mV with η ¼ 2.21%), [15] and Sinsermsuksakul et al in 2014 ((V OC ¼ 372 mV with η ¼ 4.4%). [13] To investigate the built-in potential (V bi ), acceptor and donor concentrations (N A and N D , respectively), and the depletion region of the n-type and p-type layers (w n and w p , respectively), the capacitance-reverse bias voltage (C-V ) characteristics were analyzed using Equation ( 1) and ( 2)…”

“…Hall measurements confirmed that the obtained SnS films exhibited p‐type conduction, which is similar to that of the previously reported undoped SnS thin films. [ 25 ] The conductivity, carrier concentration, and Hall mobility of a typical SnS thin film, as well as those of the n‐type SnS single crystal [ 22 ] used as the substrate for the deposition of the p‐type thin film, are shown in Table 1 . The Hall mobility of the p‐type thin film was of the same order of magnitude as the reported values of the undoped SnS thin films (1–4 cm V −1 s −1 ), which were also prepared by radio frequency (RF)‐magnetron sputtering.…”

“…Fabrication of Homojunction: The structure of the homojunction solar cell is schematically shown in Figure 1. Cl-doped n-type SnS single crystals, of which synthesis method is described in a previous study, [22] were used as the substrate for the deposition of the p-type SnS thin films. First, the surface of the n-type SnS single crystal was cleaved in air, after which a p-type SnS thin film was deposited on the (100) n-type SnS single crystal by 2 in.…”

“…In addition, we have established a flux growth technique to obtain large (>16 mm in diameter) n‐type SnS single crystals. [ 22 ] This achievement paves way for the fabrication of a pn homojunction in SnS by the deposition of a p‐type SnS thin film on an n‐type large‐sized SnS single crystal. Such a prototype homojunction device is expected to reveal the potential of the SnS‐based homojunction and thin‐film solar cells.…”

Remarkable electron and phonon transports in low-cost SnS: A new promising thermoelectric material

“…Experimentally, two strategies are adopted to realize the ntype conduction in SnS, including cation (Pb 2+ , Sb 3+ , Bi 3+ ) [95][96][97] substitution in Sn sites and halogen anion (Cl − , Br − ) [50,98,99] doping at S sites. The carrier concentration, however, is too low to achieve a good electrical conductivity.…”