FA₄Pb₂I_7.5(SCN)_0.5: n = 3 Member of Perovskite Homologous Series FA_n+1Pb_n−1I_3n−1.5(SCN)_0.5 with Columnar Defects

Hybrid organic–inorganic halide perovskites are an emerging class of optoelectronic materials. Among them, there are many homologous series of Ruddlesden–Popper and Dion–Jacobson layered perovskites reported, but a homologous series based on defect ordering has not yet been discovered. Here, by using thiocyanate anion as a defect generator, we successfully synthesized a new defect-ordered perovskite FA4Pb2I7.5(SCN)0.5 together with the previously reported FA6Pb4I13.5(SCN)0.5. These compounds can be represented respectively as n = 3 and n = 5 members of the perovskite homologous series FAn+1Pbn−1I3n−1.5(SCN)0.5 with ordered columnar defects, which is the first homologous series of defect-ordered hybrid perovskites. The optical band gap increases with an increase in the ordered defects in the lattice. FA4Pb2I7.5(SCN)0.5 (n = 3) exhibits photoluminescence emission, which is a feature of layered perovskites with a quantum-well structure. This study provides a new strategy to control the defect orderings for tuning their optical properties by incorporating thiocyanate.