Machines and electronic devices often generate waste heat that is difficult to utilize. If electricity could be generated from this waste heat, it would offer a means for a clean and sustainable power production: Such a technology would be ideally suited for low-power electronics applications such as wearables or low-cost Internet-of-Things devices. This includes, for example, wearable (medical) devices and sensors, with a wide range of applications in the healthcare and sports industry, in smart buildings and mobility applications.