  Cu-based chalcogenides are promising materials for thin-film solar cells with
more than 20% measured cell efficiency. Using first-principles calculations
based on density functional theory, the optoelectronic properties of a group of
Cu-based chalcogenides Cu$_2$-II-IV-VI$_4$ is studied. They are then screened
with the aim of identifying potential absorber materials for photovoltaic
applications. The spectroscopic limited maximum efficiency (SLME) introduced by
Yu and Zunger is used as a metric for the screening. After constructing the
current-voltage curve, the maximum spectroscopy dependent power conversion
efficiency is calculated from the maximum power output. The role of the nature
of the band gap, direct or indirect, and also of the absorptivity of the
studied materials on the maximum theoretical power conversion efficiency is
studied. Our results show that Cu$_2$-II-GeSe$_4$ with II=Cd and Hg, and
Cu$_2$-II-SnS$_4$ with II=Cd and Zn have a higher theoretical efficiency
compared to the materials currently used as absorber layer.
