Lead-free hybrid perovskite N(CH)SnI with robust ferroelectricity induced by large and non-polar N(CH) molecular cation.

The ferroelectricity in the hybrid perovskite CHNHPbI is under debate because it results from the polar molecular cation CHNH while the molecular orientation was reported to be random. Here we predict that a Pb-free hybrid perovskite N(CH)SnI with non-polar molecular cation N(CH) has strong ferroelectricity with a spontaneous polarization of 16.13 μC cm. The large polarization results from the distortion of SnI octahedron induced by the large N(CH) and is independent of the molecular orientation, so the ferroelectricity is robust. The ferroelectric R3m perovskite structure of N(CH)SnI 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(CH)SnI 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.