High Open-Circuit Voltage of a Pyroelectric Energy Harvester Based on KNN Single Crystals

Pyroelectric materials have promising applications in small generators and energy harvesters, which play the role of converting thermal energy into electricity. In particular, the open-circuit voltage is closely related to the efficiency of energy harvesting. Therefore, it is necessary to prepare pyroelectric materials with high open circuit voltage. In this work, a high open-circuit voltage of a pyroelectric energy harvester based on KNN single crystals is grown by the top-seeded solution-growth method. The open-circuit voltage of KNN single crystals is as high as 47 V. Meanwhile, the pyroelectric open-circuit voltage remains almost 90% after 50 cycles, which exhibited excellent cycle reversibility. Also, the pyroelectric coefficient of KNN single crystals can reach 9.1 × 10⁴μC·m^-2·K^-1at orthogonal-tetragonal phase transition. We also revealed the reason for the open-circuit voltage of KNN single crystals is that the motion of the domain walls and the drastic change of spontaneous polarization during the O-T phase transition lead to the enhancement of the pyroelectric coefficient by Raman spectroscopy. Furthermore, the designed energy harvester exhibits a power density of up to 773.7 mW·m^-3. Therefore, this work provides a potential material for waste heat harvesting. This is essential to resolve the contradiction between thermal energy loss and energy and to collect and reuse the lost thermal energy.