Lead-free hybrid perovskite N(CH3)4SnI3 with robust ferroelectricity induced by large and non-polar N(CH3)4+ molecular cation

The ferroelectricity in the hybrid perovskite CH3NH3PbI3 is under debate because it results from the polar molecular cation CH3NH3+ while the molecular orientation was reported to be random. Here we predict that a Pb-free hybrid perovskite N(CH3)4SnI3 with non-polar molecular cation N(CH3)4+ has strong ferroelectricity with a spontaneous polarization of 16.13 μC cm−2. The large polarization results from the distortion of SnI6 octahedron induced by the large N(CH3)4+ and is independent of the molecular orientation, so the ferroelectricity is robust. The ferroelectric R3m perovskite structure of N(CH3)4SnI3 can be synthesized as the ground state under a hydrostatic pressure over 3 GPa and remains stable under ambient pressure. Given the strong ferroelectricity, good stability and high visible-light absorption, N(CH3)4SnI3 may be an ideal light-absorber semiconductor for high-efficiency solar cells because its ferroelectric polarization can facilitate electron-hole separation and produce large bulk photovoltaic effect, making the design of homogeneous bulk photovoltaic devices possible.