Stable 6H Organic–Inorganic Hybrid Lead Perovskite and Competitive Formation of 6H and 3C Perovskite Structure with Mixed A Cations

We report the synthesis and properties of a new organic–inorganic hybrid lead perovskite (OIHP), azetidinium lead bromide (AzPbBr3), possessing the 6H perovskite structure (space group P63/mmc with a = 8.745 Å and c = 21.329 Å). This compound has a band gap of 2.81 eV and remains stable for >6 months in the ambient environment. DFT simulations are in fairly good agreement with experiments and indicate that AzPbBr3 is a direct band gap semiconductor. A partial solid solution with the cubic (3C) perovskite methylammonium lead bromide (Az1–xMAxPbBr3) is possible. In Az-rich 6H compositions the lattice volume and band gap are invariant with x (≤0.3), whereas in the MA-rich 3C phase (0.8 ≤ x ≤ 1.0) the lattice parameters and band gap increase with increasing Az content. Although the relatively large band gap of AzPbBr3 makes it unsuitable for photovoltaic applications, the results indicate Az+ is a suitable alternative organic A cation for band gap tuning of OHIPs.