Control of Halogen Atom in Inorganic Metal‐Halide Perovskites Enables Large Piezoelectricity for Electromechanical Energy Generation

Abstract

Regulating the strain of inorganic perovskites has emerged as a critical approach to control their electronic and optical properties. Here, an alternative strategy to further control the piezoelectric properties by substituting the halogen atom (I/Br) in the CsPbX3 perovskite (X = Cl, Br) structure is adopted. A series of piezoelectric materials with excellent piezoelectric coefficients (d33) are unveiled. Iodine‐incorporated CsPbBr2I demonstrates the record intrinsic piezoelectric response (d33 ≈47 pC N−1) among all inorganic metal halide perovskites. This leads to an excellent electrical output power of ≈ 0.375 mW (24.8 µW cm−2 N−1) in the piezoelectric energy generator (PEG) which is higher than those of the pristine/mixed perovskite references with CsPbX3 (X = I, Br, Cl). With its structural phase remaining unchanged, the strained CsPbBr2I retains its superior piezoelectricity in both thin film and nanocrystal powder forms, further demonstrating its repeatability and versatility of applications. The origin of high piezoelectricity is found to be due to halogen‐induced anisotropic lattice strain in the unit‐cell along the c‐axis, and octahedral distortion. This study reveals an avenue to design new piezoelectric materials by modifying their halide constituents and paves the way to design efficient PEGs for improved electromechanical energy conversion.

Piezoelectric Charge Coefficient of Halide Perovskites

“…The origin of d 33 enhancement is mainly ascribed to the increased BX 6 octahedral distortion in the lattice and the off-centring of the B atoms [58,60,62]. Chen et al [45] and Khan et al [61] reported that applying a poling voltage of 3 V and 40 V during the PFM measurement was enough to observe the domain switching during the PFM measurement.…”

“…The grain size effect on the piezoelectric properties of halide perovskites has not been exploited in detail so far. However, recently, Khan et al [61] reported that a large grain size (~200 nm) is important for enhanced d 33 values, and the authors attribute this to the easier displacement of domain walls in larger grains. The grain size information is not reported for all the halide perovskites listed in Tables 1 and 2.…”

“…The grain size information is not reported for all the halide perovskites listed in Tables 1 and 2. However, based on the data available, the grain size of some of the piezoelectric halide perovskites (CsPbI 3 [58], CsPbBr 3 [59], MASnI 3 [60], CsPbI 2 Br [61], and MDABCO-NH4I 3 [52]) listed in Tables 1 and 2 ranges from 200 to 500 nm.…”

“…The reported d 33 values range from 12 pC/N to 47 pC/N. The CsPbIBr 2 showed the highest d 33 coefficient of 47 pC/N, as measured using the vertical-PFM method[61].…”

Tuning ferroelectric phase transition temperature by enantiomer fraction

“…Since these properties and functions are directly related to ferroelectric phase transitions, controlling and tuning the phase transition temperature or Curie temperature ( T C ) is the key to optimizing the performances of ferroelectric materials for various applications 31 . Common approaches to tuning the T C mainly focus on controlling the chemical compositions, including H/D isotope substitution 32 – 35 , H/F substitution 36 , 37 , metal/cation/anion doping 24 , 38 , etc 39 . These approaches can alter the local intermolecular interactions and structural symmetries of the crystals and thereby affect the T C 40 .…”