Synthesis and Electronic Structure of Mid-Infrared Absorbing Cu 3 SbSe 4 and Cu x SbSe 4 Nanocrystals.

Aliovalent I-V-VI semiconductor nanocrystals are promising candidates for thermoelectric and optoelectronic applications. Famatinite Cu 3 SbSe 4 stands out due to its high absorption coefficient and narrow band gap in the mid-infrared spectral range. This paper combines experiment and theory to investigate the synthesis and electronic structure of colloidal Cu x SbSe 4 nanocrystals. We achieve predictive composition control of size-uniform Cu x SbSe 4 ( x = 1.9-3.4) nanocrystals. Density functional theory (DFT)-parametrized tight-binding simulations on nanocrystals show that the more the Cu-vacancies, the wider the band gap of Cu x SbSe 4 nanocrystals, a trend which we also confirm experimentally via FTIR spectroscopy. We show that Sb Cu antisite defects can create mid-gap states, which may give rise to sub-bandgap absorption. This work provides a detailed study of Cu x SbSe 4 nanocrystals and highlights the potential opportunities as well as challenges for their application in infrared devices.