Ternary alloy nanocrystals of tin and germanium chalcogenides

Abstract

Tin (Sn) and germanium (Ge) chalcogenides have recently gained popularity as potential alternatives to the toxic lead chalcogenides, due in part to their relatively higher chemical and environmental stability, for use in photovoltaic devices. Herein, we report the synthesis of ternary composition chalcogenide, i.e., Sn_xGe_1−xS, Sn_xGe_1−xSe, GeS_xSe_1−x, and SnS_xSe_1−x, nanocrystals (NCs) by novel gas-phase laser photolysis. A full series of completely miscible alloy nanocrystals, the band gaps of which could be tuned to cover a wide range (0.9–1.6 eV), were obtained by facile composition tuning through adept control of the relative pressure of the precursors. Two cation alloy (Sn_xGe_1−xS and Sn_xGe_1−xSe) NCs exhibited unique anisotropic bowing phenomena of the orthorhombic phase lattice constants, but the anion alloy (GeS_xSe_1−x and SnS_xSe_1−x) NCs did not. The cation alloy NCs showed optical bowing, which is well correlated with the bowing of the lattice parameters. The Sn_xGe_1−xS and SnS_xSe_1−x NCs showed remarkably higher photoconversion efficiency in photovoltaic and photodetector devices when compared with that of end members.