Study of pnictides for photovoltaic applications

Abstract: For the transition into a sustainable mode of energy usage, it is important to develop photovoltaic materials that exhibit better solar-to-electricity conversion efficiencies, a direct optimal band gap, and made of non-toxic, earth abundant elements compared to the state-of-the-art silicon photovoltaics. Here, we explore the non-redox-active pnictide chemical space, including binary A$_3$B$_2$, ternary AA'$_2$B$_2$, and quaternary AA'A"B$_2$ compounds (A, A', A" = Ca, Sr, or Zn; B = N or P), as candidate beyond-Si photovoltaics using density functional theory calculations. Specifically, we evaluate the ground state configurations, band gaps, and 0 K thermodynamic stability for all 20 pnictide compositions considered, besides computing the formation energy of cation vacancies, anion vacancies, and cation anti-sites in a subset of candidate compounds. Importantly, we identify SrZn$_2$N$_2$, SrZn$_2$P$_2$, and CaZn$_2$P$_2$ to be promising candidates, exhibiting optimal (1.1-1.5 eV) hybrid-functional-calculated band gaps, stability at 0 K, and high resistance to point defects (formation energies $>$1 eV), while other possible candidates include ZnCa$_2$N$_2$ and ZnSr$_2$N$_2$, which may be susceptible to N-vacancy formation. We hope that our study will contribute to the practical development of pnictide semiconductors as beyond-silicon light absorbers.