Controlling the size, shape, phase, band gap, and localized surface plasmon resonance of Cu_2-xS and Cu_xIn_yS nanocrystals

We show how indium incorporation can effect the size, morphology, crystal structure, and optical properties of CIS nanocrystals (NCs) and demonstrate a robust methodology for preparing monodisperse plasmonic and nonplasmonic CIS NCs. In contrast with previous methods of producing CIS nanocrystals exhibiting localized surface plasmon resonance (LSPR), which employed expensive and hazardous bis(trimethylsilyl) sulfide, we employ sulfur dissolved in oleic acid as the sulfur donor in combination with appropriate cation precursors to allow production of monodisperse CIS NCs with broad variation of the Cu:In ratio in the products. The crystal phase of the CIS NCs is determined not only by the reactivity of the ligands but also by the cation composition. The LSPR shifted to longer wavelengths with increasing In content until it vanished, while the band gap of the CIS NCs decreased linearly from 2.1 to 1.2 eV. The manipulation of optical properties of CIS NCs with controlled and well-defined size, shape, and phase may open up new possibilities for applying I-III-VI materials in solution-processed optoelectronic devices.