Pyroelectricity is defined as the temperature dependence of the spontaneous polarization in specific anisotropic solid. The temperature change of a pyroelectric material causes the net dipole moment to vary. The redistribution of free charges to compensate for the change in bound charge results in a pyroelectric current flow through external circuits. Despite the long history of the material, the practical application of pyroelectric materials has been limited to infra-red sensors, due to the large thermal mass of bulk pyroelectric materials, poor pyroelectric properties, and low thermal stability. To overcome such challenges, we aim to tailor the pyroelectric properties of thin single crystalline PMN-PT films via controlling strain, composition, and microstructures. We are also developing pyroelectric thermal energy converters with a large power density by incorporating the engineered thin freestanding PMN-PT films. The proposed pyroelectric converter uses a thermal fluctuation instead of the large thermal gradient across the material; therefore it can operate without requiring a significant cooling power, which will provide substantial benefits for a wide range of applications.