Printed flexible thermoelectric materials and devices

The innate capability of direct heat–electricity conversion endows thermoelectric (TE) materials with great application potential in the fields of low-grade heat harvesting, solid-state cooling, and sensing. Recently, the rapid development of information technology such as the Internet of Things and the popularization of wearable electronic devices have stimulated a period of prosperity for the research on flexible thermoelectric (FTE) devices. At the same time, the research on printed electronics (PEs) is expected to provide scalable and cost-effective manufacturing approaches for FTE devices. This review focuses on the recent progress in printed flexible thermoelectric (PFTE) devices and their applications. At first, the fundamental theories behind TEs and the related performance optimization strategies for FTE devices, as well as the history and applications of PEs, are introduced. Then, the state-of-the-art materials adopted in FTE devices, including materials for TE legs, solvents, dispersants, surfactants, and adhesives for printable inks/pastes, substrates, and electrodes, and the related printing methods are summarized. Subsequently, the applications and device performance of PFTE devices in thermoelectric generators (TEGs), thermoelectric coolers (TECs) and thermoelectric sensors (TESs) over the last decade are reviewed. At last, the challenges existing currently in the PFTE field are discussed and some perspectives on the future investigations toward high-performance, low-cost PFTE devices are proposed.