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

[Image: see text] 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.