Novel Defect Imide Double Antiperovskites AE5AsPn(NH)2 (AE = Ca, Sr; Pn = Sb, Bi) as Potential Solar Cell Absorber Materials

An abundance of oxide, halide and chalcogenide perovskites have been explored with outstanding properties, while the emerged nitride perovskites are extremely rare due to the challenging synthesis. By inverting the ion type in the perovskite structure, the antiperovskite structure is obtained. Among them, ternary antiperovksite nitrides X₃AN (X = Ba, Sr, Ca, Mg; A = As, Sb) have recently been identified as exhibiting excellent optoelectronic properties. To explore the undiscovered composition space of perovskite-structured nitrides, the ammonothermal method was applied, from which three new layered quaternary imide-based defect-antiperovskites AE₅AsPn(NH)₂ (AE = Ca, Sr; Pn = Sb, Bi) were obtained. These new imide compounds feature a distorted square-pyramidal coordination geometry around the imide-group (Ca₅NH). Layers of Ca²⁺ vacancies can be found with an alternating As^3- and Pn^3- (Pn^3- = Sb^3-, Bi^3-) coordination along the A-site, displaying a two-dimensional (2D) structural dimensionality. All three AE₅AsPn(NH)₂ compounds show suitable direct band gaps within the visible-light region. Density functional theory calculations reveal good band dispersion, transport properties and optical properties, especially along the out-of-plane direction, demonstrating their 3D character of electronic transport. The narrow tunable direct band gaps and appealing charge carrier properties make AE₅AsPn(NH)₂ promising candidates as solar cell absorber materials.