  Zinc phosphide (Zn3P2) has had a long history of scientific interest largely
because of its potential for earth-abundant photovoltaics. To realize
high-efficiency Zn3P2 solar cells, it is critical to understand and control
point defects in this material. Using hybrid functional calculations, we assess
the energetics and electronic behavior of intrinsic point defects and hydrogen
impurities in Zn3P2. All intrinsic defects are found to act as compensating
centers in p-type Zn3P2 and have deep levels in the band gap, except for zinc
vacancies which are shallow acceptors and can act as a source of doping. Our
work highlights that zinc vacancies rather than phosphorus interstitials are
likely to be the main source of p-type doping in as-grown Zn3P2. We also show
that Zn-poor and P-rich growth conditions, which are usually used for enhancing
p-type conductivity of Zn3P2, will facilitate the formation of certain
deep-level defects (P_Zn and P_i) which might be detrimental to solar cell
efficiency. For hydrogen impurities, which are frequently present in the growth
environment of Zn3P2, we study interstitial hydrogen and hydrogen complexes
with vacancies. The results suggest small but beneficial effects of hydrogen on
the electrical properties of Zn3P2.
