Bi(Sb)NCa3: Expansion of Perovskite Photovoltaics into All-Inorganic Anti-Perovskite Materials

Perovskite photovoltaics (PVs) have attracted intense interest largely because of their high power conversion efficiency and low cost. The chemical structures of perovskite materials can be generally described by the formula of ABX(3), where cations occupy "A" and "B" sites and anions occupy "X" sites. Herein, we present a comprehensive theoretical study of two inorganic anti-perovskite materials, namely, BiNCa3 and SbNCa3, for perovskite PVs. Note that in anti-perovskites, anions occupy "A" and "B" sites, whereas cations occupy "X" sites. Specifically, for both materials, we investigate their thermodynamic stability, dynamic stability, optoelectronic properties and defect properties through ab initio calculations. Our computation suggests that both BiNCa3 and SbNCa3 possess direct band gaps of 0.65 and 1.14 eV, respectively. Notably, both predicted to be thermodynamically stable, as demonstrated by their relatively large stable region based on the phase stability analysis. Dynamic and thermal stabilities are also suggested via the computed phonon spectra and ab initio molecular dynamics simulation. Furthermore, both materials possess desired optical absorption coefficients in the visible light region, comparable to that of the prevailing organic-inorganic hybrid perovskite, MAPbI(3). Both exhibit enhanced optical absorption in the infrared region and have good defect tolerance. Lastly, good n-type and p-type conductivity may be realized by controlling the growth condition. The combined desirable properties render both BiNCa3 and SbNCa3 as promising all-inorganic and lead-free optical absorbers for PV application.