Design of Mixed-Cation Tri-Layered Pb-Free Halide Perovskites for Optoelectronic Applications

To eliminate the toxic Pb2+ cation in hybrid halide perovskites, M '(3+) cations of Bi/Sb-based layered halide perovskites are being increasingly investigated for optoelectronic applications. However, such M '(3+) trivalent cations constrain the face-sharing bioctahedral or the bi-layered perovskites required to meet the charge neutrality condition. This usually gives rise to oversized indirect bandgaps and inferior carrier transport. Recent experiment suggested a mixed-cation tri-layered halide perovskite can be obtained by sandwiching a [Cu2+X6](4-) layer between Sb3+ perovskite bilayers along the polar [111] planes with cation ordering. A material design of mixed-cation -oriented tri-layered Pb-free halide perovskite A(4)MM ' X-2(12) is studied by a computational screening of various combinations of M2+ cations (e.g., Zn2+, Sn2+) and M '(3+) cations (e.g., Bi3+, Sb3+). The thermodynamic stability of the candidate materials is systemically evaluated with respect to potential decomposition pathways and a series of stable compounds is synthesized. These results further indicate the chemical trend of electronic structure and how octahedral tilting coupling with charge ordering affects electronic properties. A protocol for engineering A(4)MM ' X-2(12) perovskites with optimized structures and electronic properties by exploiting octahedral tilting coupling with charge ordering in the polar layered perovskites is established.