Flexible photothermoelectric (PTE) detectors have considerable research significance owing to their unique characteristics, including flexibility and PTE properties.
Flexible PTE detectors have the characteristics of lightness, flexibility, and softness, allowing them to be attached directly to irregular surfaces for continuous measurement of spatial information. They have considerable potential in the development and fabrication of miniaturized energy equipment, virtual-reality interactive systems, and implantable medical devices, which have application prospects in new energy, microelectronics, artificial intelligence, medical care, and other fields. They are also attractive for use in wearable devices, as they offer several advantages over traditional rigid sensors. These detectors can be easily bent or shaped to fit the contours of the human body, which allows comfortable and unobtrusive monitoring of physiological parameters.
Furthermore, the PTE properties of these detectors allow them to have ultra-broadband responses. In contrast to other types of detectors, which are typically limited to a specific wavelength range, PTE detectors can detect light across a wide range of wavelengths, from ultraviolet to terahertz. This makes them highly versatile and useful for various applications, including spectroscopy, imaging, and sensing. Another advantage of PTE detectors is their high speed. The PTE response breaks the limit of the low response speed of traditional thermal detectors by introducing hot carrier-assisted heat conduction. This fast response makes PTE detectors well-suited for applications that require rapid detection, such as high-speed imaging and sensing. Additionally, they can operate under zero-bias and room-temperature conditions, which makes them convenient and cost-effective to use. In contrast, other types of broadband detectors, such as bolometers, typically require a bias voltage to operate and may require cooling to achieve optimal performance.
Overall, the research into flexible PTE detectors has significant implications for the development and applications of novel electronic devices. In the past 20 years, the field has continued to advance, and there has been a large amount of research on new types of flexible PTE detectors. However, they face a series of challenges related to detection performance and manufacturing process improvement. Therefore, it is necessary to provide an overview of flexible PTE detectors to lay the foundation for the development of flexible optoelectronic technology.
In this review, we first describe the key parameters of flexible PTE detectors, including the responsivity, response time, cutoff frequency, noise equivalent power, and specific detectivity. Then, we summarize the research progress of flexible PTE detectors with detection wavelengths ranging from visible to terahertz and introduce the exploration, application, and optimization mechanism of carbon materials and inorganic and organic compounds with flexible properties in the field of PTE detection. Suzuki’s research group made significant contributions to the application of CNTs in flexible PTE detectors (Fig.4). They developed a variety of flexible CNT-based PTE detectors for different use scenarios (Fig.5) and applied them to detect terahertz light (Fig.7). In addition to CNTs, many other new materials, such as reduced graphene oxide (Fig.10), topological insulators (Fig.11), transition-metal halide (Fig.12), quasi-one-dimensional materials (Fig.13), MXenes (Fig.14), and PEDOT (Fig.15) have been studied and applied to flexible PTE detectors and have exhibited good performance. Combinations of conducting polymers and carbon materials for flexible PTE detectors have been widely studied in recent years. Studies on graphene/PANI, graphene/PEI (Fig.20), and PBI/MWCNTs (Fig.21) indicated that it is easier to prepare high-performance flexible PTE detectors by combining these materials than by using them alone. Finally, the problems faced and the ongoing research trends in this field are discussed, including methods for improving the detector performance, the evaluation criteria for flexibility, and the manufacturing and human compatibility problems in practical applications.
Flexible PTE detectors can revolutionize the field of photodetectors. We expect that they will become increasingly important—particularly in the development of wearable devices and other flexible electronics. We expect to see further advancements in these detectors, including improvements in sensitivity, response time, and reliability. To achieve these goals and promote the practical application of flexible PTE detectors, it is necessary to explore new materials, design the detector structure, and formulate unified evaluation standards.
