The phase diagram of a mixed halide (Br, I) hybrid perovskite obtained by synchrotron X-ray diffraction.

Frederike Lehmann,Alexandra Franz,Susan Schorr,Andreas Taubert,Thomas Unold,Daniel M Többens,Sergej Levcenco

doi:10.1039/c8ra09398a

Abstract

By using synchrotron X-ray powder diffraction, the temperature dependent phase diagram of the hybrid perovskite tri-halide compounds, methyl ammonium lead iodide (MAPbI3, MA+ = CH3NH3+) and methyl ammonium lead bromide (MAPbBr3), as well as of their solid solutions, has been established. The existence of a large miscibility gap between 0.29 ≤ x ≤ 0.92 (±0.02) for the MAPb(I1−xBrx)3 solid solution has been proven. A systematic study of the lattice parameters for the solid solution series at room temperature revealed distinct deviations from Vegard's law. Furthermore, temperature dependent measurements showed that a strong temperature dependency of lattice parameters from the composition is present for iodine rich compositions. In contrast, the bromine rich compositions show an unusually low dependency of the phase transition temperature from the degree of substitution.

Highlights

Inorganic–organic – so called “hybrid” – perovskites like methyl ammonium lead iodide (CH3NH3PbI3) have gained a lot of interest as absorber materials for solar cells.[1,2] Much attention has been focused on their remarkable optoelectronic properties
In the following we will refer to the phase with larger lattice parameters as “iodine rich phase”, to the one with smaller lattice parameters as “bromine rich phase”
By analyzing the lattice parameters obtained by Le Bail re nement of the X-ray powder diffraction pattern, a linear dependency of the chemical composition on the iodine rich mixed crystals of the MAPb(I1ÀxBrx)[3] solid solution series was revealed, showing a behavior according to Vegard's law

Summary

Introduction

Inorganic–organic – so called “hybrid” – perovskites like methyl ammonium lead iodide (CH3NH3PbI3) have gained a lot of interest as absorber materials for solar cells.[1,2] Much attention has been focused on their remarkable optoelectronic properties. Perovskite solar cells are solution-processed, which compared to other photovoltaic technologies is a cost-effective alternative for photovoltaic device fabrication.[5,9] As the bandgap is directly related to the chemical composition of the semiconductor, bandgap tuning is possible by using solid solutions, offering tailor-made devices. Hybrid perovskites are very promising lowcost alternatives for application in tandem or multijunction

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