Organic-Inorganic Hybrid Gold Halide Perovskites: Structural Diversity through Cation Size

Crystal structures of a series of organic-inorganic hybrid gold iodide perovskites, formulated as A₂ [Au^I I₂ ][Au^III I₄ ] [A=methylammonium (MA) (1) and formamidinium (FA) (2)], A'₂ [I₃ ]_1-x [Au^I I₂ ]_x [Au^III I₄ ] [A'=imidazolium (IMD) (3), guanidinium (GUA) (4), dimethylammonium (DMA) (5), pyridinium (PY) (6), and piperizinium (PIP) (7)], systematically changed depending on the cation size. In addition, triiodide (I₃ ^- ) ions were partly incorporated into the AuI₂ ^- sites of 3-7, whereas they were not incorporated into those of 1 and 2. Such a difference comes from the size of the organic cation. Optical absorption spectra showed characteristic intervalence charge-transfer bands from Au^I to Au^III species, and the optical band gap increased as the size of the cation became larger.