Contribution of Anisotropic Lattice‐Strain to Piezoelectricity and Electromechanical Power Generation of Flexible Inorganic Halide Thin Films

Abstract Strain engineering has recently emerged as a critical strategy in improving the optoelectronic properties of perovskite halide materials. However, the effects of lattice strain on piezoelectricity and related device performance have not been realized in perovskite halides. Herein, an in situ‐strain‐engineering method is proposed to induce a compressive or tensile strain of up to 0.75% for flexible inorganic–halide CsPbBr 3 thin films, resulting in anisotropic lattice strain, e.g., a contraction in the ab ‐plane and elongation along the c ‐axis in the case of compressive strain. The optimal piezoelectric energy harvesting values of ≈22.6 V and ≈1.13 µA are achieved, which are nearly 3.8 and 7.1 times better than those of the unstrained reference, for the compressively 0.75%‐strained CsPbBr 3 thin films further optimized with electric poling. These output values are the best so far compared to any previously reported values for perovskite‐halide‐based thin‐film harvesters. The structural origins of these superlative results are systematically revealed to be associated with the distortion of coupled PbBr 6 octahedra and the atomic displacement within each octahedron.