Structural analysis of formamidimium-methylammonium lead iodide perovskite binary alloy from first-principles

S. TINTE; M. SENNO

Conferencia; Internet Conference on Theory and Computation of Halide Perovskites; 2020

Fundació Scito

A notable feature in hybrid lead halide perovskites APbX3 is the peculiar interaction between the organic and inorganic degrees of freedom, which plays a crucial role in their structural, vibrational, optical and transport properties. Compositional engineering is an attractive way to tune their properties. In the mixed A-site cation methylammonium/formamidinium (MA/FA) lead iodide perovskites FA1-xMAxPbI3, the variation of the MA/FA composition allows tailoring the lattice parameters and electronic properties. However, an atomistic exploration of the full composition is missing. Here, we analyze the variation of the structural properties of  FA1-xMAxPbI3 by performing DFT calculations. Assuming a pseudocubic cell for all compositions, the linear variation of the volume and the band gap of the solid solutions between the two end compounds MAPbI3 and FAPbI3 is observed in agreement with experimental results. The cation replacement at the A-site causes a local change in cell volume accompanied by an increase tilting of the inorganic PbI6 octahedra. We confirm the fundamental role played by hydrogen bonds in the solid solution as happens in the two parent compounds. Our results provide insights on the role played by organic cation mixing at A sites in the physics of metal halide perovskites.