We have fabricated pn-junction devices based on layers of copper-zinc-tin-sulfide, Cu2ZnSnS4 (CZTS) and copper-diffused silver indium disulfide (AgInS2@Cu) ternary nanocrystals. The pn-junctions under an illumination condition have acted as solar cells due to the depletion region which was responsible for separation of charge carriers due to a drift of minority carriers across the junction by the electric field at the junction. From the capacitance-voltage characteristics of the pn-junctions, we have evaluated the width of the depletion region that extended to the two layers separately. This has enabled us to fabricate a device with a predetermined thickness of the p- and the n-type layers so that the device becomes fully-depleted. By forming such a device, we could eliminate the sections of the p- and the n-layers that would otherwise have increased the internal resistance of the solar cells without contributing to short-circuit current. (c) 2014 Elsevier B.V. All rights reserved.