  Lattice defects affect the long-term stability of halide perovskite solar
cells. Whereas simple point defects, i.e., atomic interstitials and vacancies,
have been studied in great detail, here we focus on compound defects that are
more likely to form under crystal growth conditions, such as compound vacancies
or interstitials, and antisites. We identify the most prominent defects in the
archetype inorganic perovskite CsPbI$_3$, through first-principles density
functional theory (DFT) calculations. We find that under equilibrium conditions
at room temperature, the antisite of Pb substituting Cs forms in a
concentration comparable to those of the most prominent point defects, whereas
the other compound defects are negligible. However, under nonequilibrium
thermal and operating conditions, other complexes also become as important as
the point defects. Those are the Cs substituting Pb antisite, and, to a lesser
extent, the compound vacancies of PbI$_2$ or CsPbI$_3$ units, and the I
substituting Cs antisite. These compound defects only lead to shallow or
inactive charge carrier traps, which testifies to the electronic stability of
the halide perovskites. Under operating conditions with a quasi Fermi level
very close to the valence band, deeper traps can develop.
