  Note: This paper has been published in Physical Chemistry Chemical Physics,
which can be viewed at the following URL: http://doi.org/10.1039/C5CP03102H
Cs2SnI6, a rarely studied perovskite variant material, is recently gaining a
lot of interest in the field of photovoltaics owing to its nontoxity,
air-stability and promissing photovoltaic properties. In this work, we report
intrinsic defects in Cs2SnI6 using first-principles density functional theory
calculations. It is revealed that iodine vacancy and tin interstitial are the
dominant defects that are responsible for the intrinsic n-type conduction in
Cs2SnI6. Tin vacancy has a very high formation energy (>3.6 eV) due to the
strong covalency in the Sn-I bonds and is hardly generated for p-type doping.
All the dominant defects in Cs2SnI6 have deep transition levels in the band
gap. It is suggested that the formation of the deep defects can be suppressed
significantly by employing an I-rich synthesis condition, which is inevitable
for photovoltaic and other semiconductor applications.
