Chemical strain engineering of MAPbI${}_3$ perovskite films

This study introduces a new chemical method for controlling the strain in methylammonium lead iodide (MAPbI${}_3$) perovskite crystals by varying the ratio of Pb(Ac)${}_2$ and PbCl${}_2$ in the precursor solution. To observe the effect on crystal strain, a combination of piezoresponse force microscopy (PFM) and X-ray diffraction (XRD) is used. The PFM images show an increase in the average size of ferroelastic twin domains upon increasing the PbCl${}_2$ content, indicating an increase in crystal strain. The XRD spectra support this observation with strong crystal twinning features that appear in the spectra. This behavior is caused by a strain gradient during the crystallization due to different evaporation rates of methylammonium acetate and methylammonium chloride as revealed by time-of-flight secondary ion mass spectroscopy and grazing incidince X-ray diffraction measurements. Additional time-resolved photoluminescence shows an increased carrier lifetime in the MAPbI${}_3$ films prepared with higher PbCl${}_2$ content, suggesting a decreased trap density in films with larger twin domain structures. The results demonstrate the potential of chemical strain engineering as a simple method for controlling strain-related effects in lead halide perovskites. (© 2022 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)