Piezoelectricity of lead-free hybrid perovskite monolayer (ATHP)₂XY₄ (X = Ge, Sn; Y = Cl, Br, I): Cross-scale calculation and simulation

Two-dimensional (2D) piezoelectric material is the core part of all kinds of micro-piezoelectric devices (piezoelectric energy harvesters, piezoelectric sensors, etc.). Based on the first principle, this paper theoretically predicts a kind of organic-inorganic lead-free hybrid perovskite monolayer (ATHP)(2)XY4 (X = Ge, Sn; Y = Cl, Br, I) with a large out-of-plane piezoelectric coefficient (d(31)). Combined with the finite element simulation, it shows excellent performance in the piezoelectric energy harvester. Through the first-principles theoretical calculation, the density, elastic tensor, piezoelectric stress tensor, and dielectric coefficient of the (ATHP)(2)XY4 monolayer can be obtained. The thermodynamic stability and mechanical stability of the materials are judged by ab initio molecular dynamics and stress-strain relationship analysis, respectively. The piezoelectric coefficient of the material is calculated, in which the d(31) of (ATHP)(2)SnBr4 is the largest (d(31) = 35.04 pm/V), which is still 7 times that of the bulk AlN and at least one order of magnitude larger than that of other 2D materials. The finite element simulation results of a simple piezoelectric beam show that the voltage output of the piezoelectric beam reaches 27.79 V. Our research shows that lead-free hybrid perovskite monolayer (ATHP)(2)XY4 has strong competitiveness in the application of environment-friendly and bio-friendly micro-piezoelectric devices. In addition, the cross-scale simulation method from the first principles to the finite element method is of great significance for the optimization of micro-piezoelectric devices.