Output characteristics of thin-film flexible piezoelectric generators: A numerical and experimental investigation

Flexible piezoelectric generators are promising energy harvesters for future self-powered electronics by converting surrounding mechanical energy into electricity. Although many types of flexible piezoelectric generators have been demonstrated, their output behaviors are still not systematically reported due to the complexity since the behaviors depend on many ingredients including piezoelectric device parameters and external mechanical energy conditions. In this research, numerical simulations based on a buckle-bending model were carried out to systematically investigate the output characteristics of flexible piezoelectric generators. The reliability of the numerical results were verified through experimentation using group III-nitride thin-film flexible piezoelectric generators. The ideal open-circuit voltage and short-circuit current density are proportional to the strain and strain rate of the piezoelectric material, respectively. For a specific device at a certain mechanical condition, the piezoelectric output varies with load resistance and shows a maximum power density at a certain load resistance, i.e., optimum load resistance. The optimum load resistance increases linearly with piezoelectric material thickness, inverse of device area, and bending time, while does not change with flexible substrate thickness, and bending extent. The optimum power density increases linearly with piezoelectric material thickness, square of flexible substrate thickness, inverse of bending time, and bending extent, while does not change with device area. The detailed understanding of the output characteristics of flexible piezoelectric generators can help the optimization of device configuration for better piezoelectric energy harvesting.