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

Abstract

even higher strain-stress field is likely created within the perovskite lattices than in the case of rigid substrates because of the larger thermal expansion mismatch with the flexible polymer substrates and the operations that induce intense stress, such as bending, stretching, twisting, and folding. [8][9][10] On the other hand, the additional strain present in the flexible perovskite structure can positively influence the piezoelectric properties of the materials, if properly applied, by inducing the extensive distortion of octahedral structure and thus the surface polarization.Herein, we propose a strain-engineering technique that enables intentionally imposing in situ compressive or tensile strain. As a representative all-inorganic halide material, we employed CsPbBr 3 in the form of a flexible thin film to explore its strain-dependent piezoelectricity for use in harvesting electromechanical energy under bending operation. Despite the variety of potential anisotropic halide compounds, piezoelectricity in perovskite halides has rarely been demonstrated experimentally, probably because of the difficulty of securing high-quality samples due to the limited availability of appropriate chemical precursors and synthesis methods. Table S1 (Supporting Information) summarizes the reported piezoelectric coefficients of halide materials, [11][12][13][14][15][16][17][18][19][20][21] which were obtained from both experiments and theoretical simulations. Apart from the reported theoretical estimations of piezoelectricity, [11,12] the local piezoresponse as characterized by piezoresponse force microscopy (PFM) is usually used to define the effective piezoelectric coefficient d 33,eff for synthesized halide materials. [13][14][15][19][20][21] For example, a d 33,eff value of 6 pm V −1 was reported for methylammonium lead iodide (MAPbI 3 ) thin films as a result of PFM measurements. [14] As another example, MASnI 3 thin films revealed a high d 33,eff of 20.8 pm V −1 with a well-developed butterfly loop. [15] Typically, the experimental piezoelectric coefficient ranged from 0.32 to 38 pm V −1 , [13][14][15][16][17][18][19][20][21] while the theoretical values were in the range of 4.1 to 31.4 pC N −1 , [11,12] which depended on halide composition (e.g., organic-inorganic versus inorganic compounds and B-site substitutions in ABX 3 structure) and the type of material (e.g., single-crystal, nanoparticle, and thin film) as summarized in Table S1 (Supporting Information).The enhanced piezoelectricity achieved by applying the in situ strain here was further verified by demonstrating the

Development of Low-Resistance Ohmic Contacts with Bilayer NiO/Al-Doped ZnO Thin Films to p-type GaN

“…The films annealed at 600 °C show a slightly higher value of the lattice constant c than that annealed at lower temperatures, thereby giving a higher value of stress. The negative sign of stress indicates that the stress is compressive in nature for all films. , As a result of compressive forces, the lattice constant c is elongated, and therefore, AZO unit cells are under the state of elongation. Moreover, the estimated value of crystallite size for all AZO films is in the range of 55–95 nm.…”

“…The negative sign of stress indicates that the stress is compressive in nature for all films. 31,32 As a result of compressive forces, the lattice constant c is elongated, and therefore, AZO unit cells are under the state of elongation. Moreover, the estimated value of crystallite size for all AZO films is in the range of 55−95 nm.…”

Laser-Shock-DrivenIn SituEvolution of Atomic Defect and Piezoelectricity in Graphitic Carbon Nitride for the Ionization in Mass Spectrometry

“…This increment resulted from the lattice strain in the laser-irradiated g-C 3 N 4 NS, as observed in the HR-XRD data, indicating the presence of residual in-plane tensile strain in the g-C 3 N 4 NS irradiated with a laser of ≤348.4 MW cm –2 . The prestress reportedly facilitates the alignment of electric dipoles, thus enhancing the piezoelectricity. , However, a more intense laser pulse deteriorated the piezoelectric performance by severely introducing atomic defects and lowering the crystallinity of the g-C 3 N 4 NS. As demonstrated in the above-mentioned DFT results for the dipole moment calculation, high crystallinity of the g-C 3 N 4 NS comprising more non-centrosymmetric triangular nanoholes was responsible for the superior piezoelectric performance.…”

Origin of the anisotropic-strain-driven photoresponse enhancement in inorganic halide-based self-powered flexible photodetectors

“…Strain engineering is widely recognized as a strategy for modulating optoelectronic properties by taking advantage of stress-driven changes in the band structure, which arise from changes in the crystal structure, such as the bond angle and bond length. 19–22 The strain engineering of halides has been reported, mostly for use in solar cells or on the basis of theoretical analysis. Specifically, an intentional strain was experimentally imposed by substitution-driven stress, 23 annealing at high temperatures, 20 and thermal mismatch with the substrate.…”

“…20 Theoretical calculations on MAPbI 3 suggested the possibility of large fluctuations in the band structure and density of states over a compressive-to-tensile-strain range of up to 4%. 21…”