Br-doped n-type SnS single crystals with carrier concentrations suitable for homojunction solar cells

Abstract

SnS has attracted considerable attention as a semiconductor material for use in thin-film solar cells. In particular, fabricating a SnS homojunction is essential for achieving highly efficient solar cells. However, controlling the n-type SnS carrier concentration to the optimum level of 1015–1016 cm−3 is currently challenging. Herein, we report a doping strategy for n-type SnS and the fabrication of n-type single crystals with a carrier concentration of ∼1016 cm−3 using Br as the dopant. Br-doped single crystals were grown using SnBr2 as the flux, while Cl-doped single crystals were grown as a reference using the same method. Cl-doped SnS exhibited a carrier concentration of ∼1018 cm−3, whereas Br-doped SnS realized a concentration of 3.2 × 1016 cm−3. The Br-doped crystals exhibited thermal-activation-type behavior based on the temperature dependence of the carrier concentration, with an activation energy of 52 meV determined. X-ray photoelectron spectroscopy revealed that Br- and Cl-doped SnS exhibit Fermi levels at 0.22 and 0.15 eV relative to the bottom of the conduction band, respectively. Furthermore, the measured electrical and electronic properties suggested that Br-doped SnS has a lower Fermi level than Cl-doped SnS. These results indicate that Br-doped SnS is suitable for forming n-layers in SnS homojunction solar cells.