Pyroelectric nanogenerators (PyNGs) in converting thermal energy into electrical energy: Fundamentals and current status

Highlights: • This study is a review on PyNGs and provides a summary of the studies in the literature. • In the article, the electrodes and mechanism of PyNGs are examined in detail. • At the end of the article, suggestions are made for the researchers. Nowadays, getting energy from natural resources has become an area of interest for researchers with the increasing demand for renewable energy sources. Like triboelectric (TENG) and piezoelectric nanogenerators (PENG), which generate electrical energy from mechanical energy, pyroelectric nanogenerators (PyNG) can also convert the waste heat in the environment into electrical energy through pyroelectric materials. Especially with the integration of PyNG into wearable electronics, the wasted heat in the environment can easily and effortlessly be made ready for use. Besides, PyNGs can be integrated into masks that have become an indispensable part of our lives with the Covid-19 pandemic, which has become a global health problem today and affected the whole world. Wearable electronics' energy requirement can be met by converting waste heat into electrical energy without any extra effort. In this paper, the theory of the pyroelectric effect, pyroelectric materials, and the structure of PyNGs, and the latest developments in micro/nanoscale devices are presented; efficient materials and future challenges opportunities are discussed.