Conducting Layered Organic-inorganic Halides Containing 〈110〉-Oriented Perovskite Sheets

Single crystals of the layered organic-inorganic perovskites, [NH 2 C(I)=NH 2 ] 2 (CH 3 NH 3 ) m Sn m I 3 m +2 , were prepared by an aqueous solution growth technique. In contrast to the recently discovered family, (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n -1 Sn n I 3 n +1 , which consists of 〈100〉-terminated perovskite layers, structure determination reveals an unusual structural class with sets of m 〈110〉-oriented CH 3 NH 3 SnI 3 perovskite sheets separated by iodoformamidinium cations. Whereas the m = 2 compound is semiconducting with a band gap of 0.33 ± 0.05 electron volt, increasing m leads to more metallic character. The ability to control perovskite sheet orientation through the choice of organic cation demonstrates the flexibility provided by organic-inorganic perovskites and adds an important handle for tailoring and understanding lower dimensional transport in layered perovskites.