Synthesis and Electronic Structure of Mid-Infrared Absorbing Cu3SbSe4 and Cu x SbSe4 Nanocrystals

Aliovalent I-V-VI semiconductor nanocrystalsarepromising candidates for thermoelectric and optoelectronic applications.Famatinite Cu3SbSe4 stands out due to its highabsorption coefficient and narrow band gap in the mid-infrared spectralrange. This paper combines experiment and theory to investigate thesynthesis and electronic structure of colloidal Cu x SbSe4 nanocrystals. We achieve predictive compositioncontrol of size-uniform Cu x SbSe4 (x = 1.9-3.4) nanocrystals. Density functionaltheory (DFT)-parametrized tight-binding simulations on nanocrystalsshow that the more the Cu-vacancies, the wider the band gap of Cu x SbSe4 nanocrystals, a trend whichwe also confirm experimentally via FTIR spectroscopy. We show thatSb(Cu) antisite defects can create mid-gap states, whichmay give rise to sub-bandgap absorption. This work provides a detailedstudy of Cu x SbSe4 nanocrystalsand highlights the potential opportunities as well as challenges fortheir application in infrared devices.