Simulations of Ion Migration in Metal Halide Perovskites – Error Found and Course Correction Proposed
Solar cells based on metal halide perovskites are not only as powerful as current silicon-based ones, but they can also be manufactured easily and inexpensively.
One challenge in using metal halide perovskites is due to the mobility of the ions, which leads to deleterious phenomena that affect cell performance. Experimental studies indicate that the constituent halide ions are particularly mobile. With a better understanding of ion mobility, more efficient and durable solar cells would be possible.
To date, simulations have been used to determine the energy barrier that a halide ion must overcome to jump from one lattice site in a metal halide perovskite to the next. This is analogous to the energy required to push a ball from one valley bottom over a mountain pass to the next valley bottom.
In their publication Caution! Static Supercell Calculations of Defect Migration in Higher Symmetry ABX3 Perovskite Halides May Be Unreliable: A Case Study of Methylammonium Lead Iodide in The Journal of Physical Chemistry Letters, RWTH scientists Professor Roger A. De Souza, Dennis Kemp, Dr. Matthew Wolf, and Dr. Amr Ramadan show that simulation tools should be used with caution.
With the help of a novel thermodynamic test, the Aachen physical chemists demonstrate that previous simulation studies used unstable “valley bottom” configurations. As a result, the energy barrier height for halide ion jumps was greatly overestimated. The experimental results presented and analyzed in the literature therefore need to be re-evaluated. Our current research results can thus be considered a scientific course correction.