Recent advances in flexible thermoelectric films and devices

Flexible thermoelectric (TE) generator (f-TEG) assembled with flexible TE films (f-TEFs), which can continuously output power by harvesting the heat energy (body heat and sunlight, etc.), is a very promising candidate to power wearable electronics and sensors. So, f-TEFs have attracted increasing attention in the last decade and made dramatic breakthrough in the last two years. In this paper, f-TEFs, which can be divided into two categories of free-standing flexible films and flexible substrate supported films, prepared by various methods, are reviewed. Strategies for improving the performance of the f-TEFs are proposed. Recent breakthroughs in f-TEFs and how these films are assembled into device designs taking advantage of their mechanical flexibility and TE properties are presented. In addition, the problems in studying f-TEFs and f-TEGs and the possible challenges are also summarized and detailed design guidelines regarding the TE properties and flexibility of the f-TEFs are provided.