Solvothermal synthesis and tunable bandgap of Cu2(Zn1-xCox)SnS4 and Cu2(Fe1-xCox)SnS4 nanocrystals

The tunable bandgap of Cu-2(Zn1-xCox)SnS4 and Cu-2(Fe1-xCox)SnS4 nanocrystals synthesized by the one-pot and hot-injection methods respectively was explored as a function of the Co concentration. The Co(CH3COO)(2) precursor is superior to Co(NO3)(2) and CoCl2 ones in enhancing the growth of pure and stoichiometric Cu2CoSnS4 (CCTS) nanocrystals. During synthesis of pure Cu-2(Zn1-xCox)SnS4 nanocrystals at 270 degrees C for 48 h in the one-pot system, Cu3SnS4 forms first and then reacts with Co to form CCTS, and finally Zn incorporates into CCTS to form the Cu-2(Zn1-xCox)SnS4 alloy. The structural transition from kesterite Cu2ZnSnS4 to stannite CCTS occurs in the Cu-2(Zn1-xCox)SnS4 samples with the Co concentration (x) in the range of 0.3-0.6. The pure Cu-2(Fe1-xCox)SnS4 nanocrystals were synthesized at 260 degrees C for 30 min by the hot-injection method. The direct bandgaps of Cu-2(Zn1-xCox) SnS4 and Cu-2(Fe1-xCox)SnS4 nanocrystals can be tuned in the ranges of 1.21-1.49 and 1.30-1.46 eV respectively, which decrease almost linearly with the Co concentration, showing that Cu-2(Zn1-xCox)SnS4 and Cu-2(Fe1-xCox)SnS4 nanocrystals may be well suited for application as the absorption layer in thermoelectric and photovoltaic devices. (C) 2015 Elsevier B.V. All rights reserved.