Conducting Layered Organic-Inorganic Halides Containing -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$_{3m+2}$, 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 $I$_{3n+1}$, which consists of -terminated perovskite layers, structure determination reveals an unusual structural class with sets of m -oriented CH$_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.