Ternary alloy nanocrystals of tin and germanium chalcogenides

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 x Ge 1−x S, Sn x Ge 1−x Se, GeS x Se 1−x , and SnS x Se 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 x Ge 1−x S and Sn x Ge 1−x Se) NCs exhibited unique anisotropic bowing phenomena of the orthorhombic phase lattice constants, but the anion alloy (GeS x Se 1−x and SnS x Se 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 x Ge 1−x S and SnS x Se 1−x NCs showed remarkably higher photoconversion efficiency in photovoltaic and photodetector devices when compared with that of end members.