Conducting layered organic-inorganic halides containing 〈110〉-oriented perovskite sheets

Single crystals of the layered organic-inorganic perovskites, [NH2C(I)=NH2]2(CH3NH 3)m SnmI3m+2, were prepared by an aqueous solution growth technique. In contrast to the recently discovered family, (C4H9NH3)2(CH3NH 3)n-1SnnI3n+1, which consists of 〈100〉-terminated perovskite layers, structure determination reveals an unusual structural class with sets of m 〈110〉-oriented CH3NH3SnI3 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.