The electronic properties of point defects in earth-abundant photovoltaic material Zn$_{3}$P$_{2}$: A hybrid functional method study

Zinc phosphide (Zn$_{3}$P$_{2})$ is an attractive and promising semiconductor for thin-film solar cell application because of its earth abundance and ease of thin-film fabrication. The electronic properties of intrinsic and extrinsic defects in Zn$_{3}$P$_{2}$ are studied by density-functional theory with hybrid functional method. Our results show that undoped Zn$_{3}$P$_{2}$ should be intrinsically $p$-type with Zn vacancies as the responsible shallow acceptors. Na or Cu doping is expected to result in improved $p$-type conductivity as compared to intrinsic Zn$_{3}$P$_{2}$. S or Al doping may lead to weak $n$-type Zn$_{3}$P$_{2}$. Doping of Mg does not produce good $n$-type Zn$_{3}$P$_{2}$, consistent with experimental observations. Contradicting to conventional wisdom, an interstitial P in Zn$_{3}$P$_{2}$ is not a triple-hole acceptor and a P vacancy in Zn$_{3}$P$_{2}$ is not a triple-electron donor. Instead, we find that the interstitial P is actually a single-hole acceptor and the P vacancy is a single-electron donor. The origins of these unusual behaviors are discussed.