Inherent Lattice Distortion Engineering via Magnetic Field for High‐Quality Strained MAPbI₃ Perovskite Single Crystals

Abstract Lattice distortion in perovskites (AMX 3 ) significantly impacts their stability and power conversion efficiency, often in a trade‐off. The inherent lattice distortion is predominantly influenced by the size, orientation, and composition of the A‐site cations. Notably, organic–inorganic hybrid lead halide perovskites with organic cations like methylammonium (MA) and formamidinium (FA) demonstrate high power conversion efficiency but compromised stability. Here, a novel synthesis method is presented for high‐quality strained MAPbI 3 single crystals that offers not only enhanced optoelectronic properties but also improved thermal stability. This technique leverages the paramagnetic nature of the MA + ion to manipulate lattice distortion. During the inverse temperature crystallization process, the dipole moment of the MA + ion aligns with the direction of the external magnetic field. Correlating Fourier‐transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) analysis demonstrates that this alignment, which induces compressive lattice strain, significantly enhances the carrier mobility from 68.1 to 487 cm 2 V s −1 , representing a sevenfold increase in hole mobility compared to the control sample. Additionally, it increases the carrier lifetime by 123%, from 23.458 to 52.364 ns, and improves thermal stability up to 230 °C. This findings reveal insights into the interplay between structural modifications and electronic properties, paving the way for tailored applications in photovoltaics, light‐emitting devices, and beyond.