Tetragonal chalcopyrite CuIn-(S1−x Se x )2 (0 ≤ x ≤ 1) nanocrystals were synthesized by reacting a mixture of CuCl, InCl3, S, and Se in the presence of oleylamine at 265 °C. The S/Se composition ratio in the CuIn(S1−x Se x )2 could be tuned across the entire composition range of x from 0 to 1 by modulating the S/Se reactant mole ratio. The tetragonal lattice constants, that is, a and c, increase linearly with the increase of Se content, following Vegard’s law. The band gap energies of CuIn(S1−x Se x )2 nanocrystals could be tuned in the range between 0.98 and 1.46 eV and change nonlinearly with respect to x, deriving a bowing parameter of 0.17 eV. In addition, the method developed in this study was scalable to achieve gram-scale production of stoichiometry-controlled CuIn(S1−x Se x )2 and CuIn1−x Ga x Se2 nanocrystals.

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