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 FA(4)Pb(2)I(7.5)(SCN)(0.5) together with the previously reported FA(6)Pb(4)I(13.5)(SCN)(0.5). These compounds can be represented respectively as n = 3 and n = 5 members of the perovskite homologous series FA(n+1)Pb(n-1)I(3n-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. FA(4)Pb(2)I(7.5)(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.